info: "See the Technical Writers assigned to Development Guidelines: https://about.gitlab.com/handbook/product/ux/technical-writing/#assignments-to-development-guidelines"
This document contains descriptions and guidelines for addressing security
vulnerabilities commonly identified in the GitLab codebase. They are intended
to help developers identify potential security vulnerabilities early, with the
goal of reducing the number of vulnerabilities released over time.
**Contributing**
If you would like to contribute to one of the existing documents, or add
guidelines for a new vulnerability type, please open an MR! Please try to
include links to examples of the vulnerability found, and link to any resources
used in defined mitigations. If you have questions or when ready for a review,
please ping `gitlab-com/gl-security/appsec`.
## Permissions
### Description
Application permissions are used to determine who can access what and what actions they can perform.
For more information about the permission model at GitLab, please see [the GitLab permissions guide](permissions.md) or the [EE docs on permissions](../../ee/user/permissions.md).
### Impact
Improper permission handling can have significant impacts on the security of an application.
Some situations may reveal [sensitive data](https://gitlab.com/gitlab-com/gl-infra/production/-/issues/477) or allow a malicious actor to perform [harmful actions](https://gitlab.com/gitlab-org/gitlab/-/issues/8180).
A common vulnerability when permission checks are missing is called [IDOR](https://owasp.org/www-project-web-security-testing-guide/latest/4-Web_Application_Security_Testing/05-Authorization_Testing/04-Testing_for_Insecure_Direct_Object_References) for Insecure Direct Object References.
Be careful to **also test [visibility levels](https://gitlab.com/gitlab-org/gitlab-foss/-/blob/master/doc/development/permissions.md#feature-specific-permissions)** and not only project access rights.
The HTTP status code returned when an authorization check fails should generally be `404 Not Found` to avoid revealing information
about whether or not the requested resource exists. `403 Forbidden` may be appropriate if you need to display a specific message to the user
about why they cannot access the resource. If you are displaying a generic message such as "access denied", consider returning `404 Not Found` instead.
Unlike other programming languages (for example, Perl or Python) Regular Expressions are matching multi-line by default in Ruby. Consider the following example in Python:
The Python example will output an empty array (`[]`) as the matcher considers the whole string `foo\nbar` including the newline (`\n`). In contrast Ruby's Regular Expression engine acts differently:
The output of this example is `#<MatchData "bar">`, as Ruby treats the input `text` line by line. To match the whole **string**, the Regex anchors `\A` and `\z` should be used.
if params[:ip] =~ /^\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}$/
render :text => `ping -c 4 #{params[:ip]}`
else
render :text => "Invalid IP"
end
end
end
```
Here `params[:ip]` should not contain anything else but numbers and dots. However this restriction can be easily bypassed as the Regex anchors `^` and `$` are being used. Ultimately this leads to a shell command injection in `ping -c 4 #{params[:ip]}` by using newlines in `params[:ip]`.
#### Mitigation
In most cases the anchors `\A` for beginning of text and `\z` for end of text should be used instead of `^` and `$`.
Consider the following example application, which defines a check using a regular expression. A user entering `user@aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa!.com` as the email on a form will hang the web server.
- [The impact of regular expression denial of service (ReDoS) in practice: an empirical study at the ecosystem scale](https://davisjam.github.io/files/publications/DavisCoghlanServantLee-EcosystemREDOS-ESECFSE18.pdf). This research paper discusses approaches to automatically detect ReDoS vulnerabilities.
- [Freezing the web: A study of ReDoS vulnerabilities in JavaScript-based web servers](https://www.usenix.org/system/files/conference/usenixsecurity18/sec18-staicu.pdf). Another research paper about detecting ReDoS vulnerabilities.
A [Server-side Request Forgery (SSRF)](https://www.hackerone.com/application-security/how-server-side-request-forgery-ssrf) is an attack in which an attacker
- Reading internal services, including cloud service metadata.
- The latter can be a serious problem, because an attacker can obtain keys that allow control of the victim's cloud infrastructure. (This is also a good reason
- When the application makes any outbound connection
### Mitigations
In order to mitigate SSRF vulnerabilities, it is necessary to validate the destination of the outgoing request, especially if it includes user-supplied information.
The preferred SSRF mitigations within GitLab are:
1. Only connect to known, trusted domains/IP addresses.
1. Use the [GitLab::HTTP](#gitlab-http-library) library
The [GitLab::HTTP](https://gitlab.com/gitlab-org/gitlab/-/blob/master/lib/gitlab/http.rb) wrapper library has grown to include mitigations for all of the GitLab-known SSRF vectors. It is also configured to respect the
`Outbound requests` options that allow instance administrators to block all internal connections, or limit the networks to which connections can be made.
In some cases, it has been possible to configure GitLab::HTTP as the HTTP
[`Gitlab::UrlBlocker`](https://gitlab.com/gitlab-org/gitlab/-/blob/master/lib/gitlab/url_blocker.rb) can be used to validate that a
provided URL meets a set of constraints. Importantly, when `dns_rebind_protection` is `true`, the method returns a known-safe URI where the hostname
has been replaced with an IP address. This prevents DNS rebinding attacks, because the DNS record has been resolved. However, if we ignore this returned
value, we **will not** be protected against DNS rebinding.
This is the case with validators such as the `AddressableUrlValidator` (called with `validates :url, addressable_url: {opts}` or `public_url: {opts}`).
Validation errors are only raised when validations are called, for example when a record is created or saved. If we ignore the value returned by the validation
when persisting the record, **we need to recheck** its validity before using it. You can learn more about [Time of Check to Time of Use bugs](#time-of-check-to-time-of-use-bugs) in a later section
There are many tricks to bypass common SSRF validations. If feature-specific mitigations are necessary, they should be reviewed by the AppSec team, or a developer who has worked on SSRF mitigations previously.
- To mitigate DNS rebinding attacks, validate and use the first IP address received.
See [`url_blocker_spec.rb`](https://gitlab.com/gitlab-org/gitlab/-/blob/master/spec/lib/gitlab/url_blocker_spec.rb) for examples of SSRF payloads. See [time of check to time of use bugs](#time-of-check-to-time-of-use-bugs) to learn more about DNS rebinding's class of bug.
Cross site scripting (XSS) is an issue where malicious JavaScript code gets injected into a trusted web application and executed in a client's browser. The input is intended to be data, but instead gets treated as code by the browser.
XSS issues are commonly classified in three categories, by their delivery method:
The injected client-side code is executed on the victim's browser in the context of their current session. This means the attacker could perform any same action the victim would normally be able to do through a browser. The attacker would also have the ability to:
- perform actions that lead to data loss/theft or account takeover
Much of the impact is contingent upon the function of the application and the capabilities of the victim's session. For further impact possibilities, please check out [the beef project](https://beefproject.com/).
For a demonstration of the impact on GitLab with a realistic attack scenario, see [this video on the GitLab Unfiltered channel](https://www.youtube.com/watch?v=t4PzHNycoKo) (internal, it requires being logged in with the GitLab Unfiltered account).
For any and all input fields, ensure to define expectations on the type/format of input, the contents, <iclass="fa fa-youtube-play youtube"aria-hidden="true"></i> [size limits](https://youtu.be/2VFavqfDS6w?t=7582), the context in which it will be output. It's important to work with both security and product teams to determine what is considered acceptable input.
- Validate the <iclass="fa fa-youtube-play youtube"aria-hidden="true"></i> [input size limits](https://youtu.be/2VFavqfDS6w?t=7582).
- Validate the input using an <iclass="fa fa-youtube-play youtube"aria-hidden="true"></i> [allowlist approach](https://youtu.be/2VFavqfDS6w?t=7816) to only allow characters through which you are expecting to receive for the field.
- When adding redirects or links to a user-controlled URL, ensure that the scheme is HTTP or HTTPS. Allowing other schemes like `javascript://` can lead to XSS and other security issues.
Note that denylists should be avoided, as it is near impossible to block all [variations of XSS](https://owasp.org/www-community/xss-filter-evasion-cheatsheet).
Once you've [determined when and where](#setting-expectations) the user submitted data will be output, it's important to encode it based on the appropriate context. For example:
- Content placed inside HTML elements need to be [HTML entity encoded](https://cheatsheetseries.owasp.org/cheatsheets/Cross_Site_Scripting_Prevention_Cheat_Sheet.html#rule-1---html-escape-before-inserting-untrusted-data-into-html-element-content).
- Content placed into a JSON response needs to be [JSON encoded](https://cheatsheetseries.owasp.org/cheatsheets/Cross_Site_Scripting_Prevention_Cheat_Sheet.html#rule-31---html-escape-json-values-in-an-html-context-and-read-the-data-with-jsonparse).
- Content placed inside <iclass="fa fa-youtube-play youtube"aria-hidden="true"></i> [HTML URL GET parameters](https://youtu.be/2VFavqfDS6w?t=3494) need to be [URL-encoded](https://cheatsheetseries.owasp.org/cheatsheets/Cross_Site_Scripting_Prevention_Cheat_Sheet.html#rule-5---url-escape-before-inserting-untrusted-data-into-html-url-parameter-values)
-<iclass="fa fa-youtube-play youtube"aria-hidden="true"></i> [Additional contexts may require context-specific encoding](https://youtu.be/2VFavqfDS6w?t=2341).
#### XSS mitigation and prevention in JavaScript and Vue
- When updating the content of an HTML element using JavaScript, mark user-controlled values as `textContent` or `nodeValue` instead of `innerHTML`.
- Avoid using `v-html` with user-controlled data, use [`v-safe-html`](https://gitlab-org.gitlab.io/gitlab-ui/?path=/story/directives-safe-html-directive--default) instead.
- Consider using [`gl-sprintf`](../../ee/development/i18n/externalization.md#interpolation) to interpolate translated strings securely.
- Avoid `__()` with translations that contain user-controlled values.
- When working with `postMessage`, ensure the `origin` of the message is allowlisted.
- Consider using the [Safe Link Directive](https://gitlab-org.gitlab.io/gitlab-ui/?path=/story/directives-safe-link-directive--default) to generate secure hyperlinks by default.
Path Traversal vulnerabilities grant attackers access to arbitrary directories and files on the server that is executing an application. This data can include data, code or credentials.
Traversal can occur when a path includes directories. A typical malicious example includes one or more `../`, which tells the file system to look in the parent directory. Supplying many of them in a path, for example `../../../../../../../etc/passwd`, usually resolves to `/etc/passwd`. If the file system is instructed to look back to the root directory and can't go back any further, then extra `../` are ignored. The file system then looks from the root, resulting in `/etc/passwd` - a file you definitely do not want exposed to a malicious attacker!
Path Traversal attacks can lead to multiple critical and high severity issues, like arbitrary file read, remote code execution or information disclosure.
- After validating the user supplied input, it should be appended to the base directory and the path should be canonicalized using the file system API.
Some methods used to construct file paths can have non-intuitive behavior. To properly validate user input, be aware
of these behaviors.
#### Ruby
The Ruby method [`Pathname.join`](https://ruby-doc.org/stdlib-2.7.4/libdoc/pathname/rdoc/Pathname.html#method-i-join)
joins path names. Using methods in a specific way can result in a path name typically prohibited in
normal use. In the examples below, we see attempts to access `/etc/passwd`, which is a sensitive file:
```ruby
require 'pathname'
p = Pathname.new('tmp')
print(p.join('log', 'etc/passwd', 'foo'))
# => tmp/log/etc/passwd/foo
```
Assuming the second parameter is user-supplied and not validated, submitting a new absolute path
results in a different path:
```ruby
print(p.join('log', '/etc/passwd', ''))
# renders the path to "/etc/passwd", which is not what we expect!
```
#### Golang
Golang has similar behavior with [`path.Clean`](https://pkg.go.dev/path#example-Clean). Remember that with many file systems, using `../../../../` traverses up to the root directory. Any remaining `../` are ignored. This example may give an attacker access to `/etc/passwd`:
```golang
path.Clean("/../../etc/passwd")
// renders the path to "etc/passwd"; the file path is relative to whatever the current directory is
path.Clean("../../etc/passwd")
// renders the path to "../../etc/passwd"; the file path will look back up to two parent directories!
As we have [moved away from supporting TLS 1.0 and 1.1](https://about.gitlab.com/blog/2018/10/15/gitlab-to-deprecate-older-tls/), you must use TLS 1.2 and above.
We recommend using the ciphers that Mozilla is providing in their [recommended SSL configuration generator](https://ssl-config.mozilla.org/#server=go&version=1.17&config=intermediate&guideline=5.6) for TLS 1.2:
-`ECDHE-ECDSA-AES128-GCM-SHA256`
-`ECDHE-RSA-AES128-GCM-SHA256`
-`ECDHE-ECDSA-AES256-GCM-SHA384`
-`ECDHE-RSA-AES256-GCM-SHA384`
And the following cipher suites (according to the [RFC 8446](https://datatracker.ietf.org/doc/html/rfc8446#appendix-B.4)) for TLS 1.3:
-`TLS_AES_128_GCM_SHA256`
-`TLS_AES_256_GCM_SHA384`
*Note*: **Golang** does [not support](https://github.com/golang/go/blob/go1.17/src/crypto/tls/cipher_suites.go#L676) all cipher suites with TLS 1.3.
##### Implementation examples
##### TLS 1.3
For TLS 1.3, **Golang** only supports [3 cipher suites](https://github.com/golang/go/blob/go1.17/src/crypto/tls/cipher_suites.go#L676), as such we only need to set the TLS version:
This example was taken [from the GitLab Agent](https://gitlab.com/gitlab-org/cluster-integration/gitlab-agent/-/blob/871b52dc700f1a66f6644fbb1e78a6d463a6ff83/internal/tool/tlstool/tlstool.go#L72).
For **Ruby**, you can use again [`HTTParty`](https://github.com/jnunemaker/httparty) and specify this time TLS 1.2 version alongside with the recommended ciphers:
There are some cases where `users` passed in the code is actually referring to a `DeployToken`/`DeployKey` entity instead of a real `User`, because of the code below in **`/lib/api/api_guard.rb`**
```ruby
def find_user_from_sources
strong_memoize(:find_user_from_sources) do
deploy_token_from_request ||
find_user_from_bearer_token ||
find_user_from_job_token ||
user_from_warden
end
end
```
### Past Vulnerable Code
In some scenarios such as [this one](https://gitlab.com/gitlab-org/gitlab/-/issues/237795), user impersonation is possible because a `DeployToken` ID can be used in place of a `User` ID. This happened because there was no check on the line with `Gitlab::Auth::CurrentUserMode.bypass_session!(user.id)`. In this case, the `id` is actually a `DeployToken` ID instead of a `User` ID.
```ruby
def find_current_user!
user = find_user_from_sources
return unless user
# Sessions are enforced to be unavailable for API calls, so ignore them for admin mode
In order to prevent this from happening, it is recommended to use the method `user.is_a?(User)` to make sure it returns `true` when we are expecting to deal with a `User` object. This could prevent the ID confusion from the method `find_user_from_sources` mentioned above. Below code snippet shows the fixed code after applying the best practice to the vulnerable code above.
## Guidelines when defining missing methods with metaprogramming
Metaprogramming is a way to define methods **at runtime**, instead of at the time of writing and deploying the code. It is a powerful tool, but can be dangerous if we allow untrusted actors (like users) to define their own arbitrary methods. For example, imagine we accidentally let an attacker overwrite an access control method to always return true! It can lead to many classes of vulnerabilities such as access control bypass, information disclosure, arbitrary file reads, and remote code execution.
Key methods to watch out for are `method_missing`, `define_method`, `delegate`, and similar methods.
### Insecure metaprogramming example
This example is adapted from an example submitted by [@jobert](https://hackerone.com/jobert?type=user) through our HackerOne bug bounty program.
Thank you for your contribution!
Before Ruby 2.5.1, you could implement delegators using the `delegate` or `method_missing` methods. For example:
```ruby
class User
def initialize(attributes)
@options = OpenStruct.new(attributes)
end
def is_admin?
name.eql?("Sid") # Note - never do this!
end
def method_missing(method, *args)
@options.send(method, *args)
end
end
```
When a method was called on a `User` instance that didn't exist, it passed it along to the `@options` instance variable.
Because the `is_admin?` method is already defined on the class, its behavior is not overridden when passing `is_admin?` to the initializer.
This class can be refactored to use the `Forwardable` method and `def_delegators`:
```ruby
class User
extend Forwardable
def initialize(attributes)
@options = OpenStruct.new(attributes)
self.class.instance_eval do
def_delegators :@options, *attributes.keys
end
end
def is_admin?
name.eql?("Sid") # Note - never do this!
end
end
```
It might seem like this example has the same behavior as the first code example. However, there's one crucial difference: **because the delegators are meta-programmed after the class is loaded, it can overwrite existing methods**:
Working with archive files like `zip`, `tar`, `jar`, `war`, `cpio`, `apk`, `rar` and `7z` presents an area where potentially critical security vulnerabilities can sneak into an application.
### Zip Slip
In 2018, the security company Snyk [released a blog post](https://snyk.io/research/zip-slip-vulnerability) describing research into a widespread and critical vulnerability present in many libraries and applications which allows an attacker to overwrite arbitrary files on the server file system which, in many cases, can be leveraged to achieve remote code execution. The vulnerability was dubbed Zip Slip.
A Zip Slip vulnerability happens when an application extracts an archive without validating and sanitizing the filenames inside the archive for directory traversal sequences that change the file location when the file is extracted.
Example malicious file names:
-`../../etc/passwd`
-`../../root/.ssh/authorized_keys`
-`../../etc/gitlab/gitlab.rb`
If a vulnerable application extracts an archive file with any of these file names, the attacker can overwrite these files with arbitrary content.
For zip files, the [`rubyzip`](https://rubygems.org/gems/rubyzip) Ruby gem is already patched against the Zip Slip vulnerability and will refuse to extract files that try to perform directory traversal, so for this vulnerable example we will extract a `tar.gz` file with `Gem::Package::TarReader`:
Always expand the destination file path by resolving all potential directory traversals and other sequences that can alter the path and refuse extraction if the final destination path does not start with the intended destination directory.
##### Ruby
```ruby
# tar.gz extraction example with protection against Zip Slip attacks.
raise "filename is outside of destination directory" unless
destination.start_with?(destination_dir + "/"))
destination
end
```
```ruby
# zip extraction example using rubyzip with built-in protection against Zip Slip attacks.
require 'zip'
Zip::File.open("/tmp/uploaded.zip") do |zip_file|
zip_file.each do |entry|
# Extract entry to /tmp/extracted directory.
entry.extract("/tmp/extracted")
end
end
```
##### Go
You are encouraged to use the secure archive utilities provided by [LabSec](https://gitlab.com/gitlab-com/gl-security/appsec/labsec) which will handle Zip Slip and other types of vulnerabilities for you. The LabSec utilities are also context aware which makes it possible to cancel or timeout extractions:
Symlink attacks makes it possible for an attacker to read the contents of arbitrary files on the server of a vulnerable application. While it is a high-severity vulnerability that can often lead to remote code execution and other critical vulnerabilities, it is only exploitable in scenarios where a vulnerable application accepts archive files from the attacker and somehow displays the extracted contents back to the attacker without any validation or sanitization of symbolic links inside the archive.
For zip files, the [`rubyzip`](https://rubygems.org/gems/rubyzip) Ruby gem is already patched against symlink attacks as it ignores symbolic links, so for this vulnerable example we will extract a `tar.gz` file with `Gem::Package::TarReader`:
STDERR.puts("archive file does not exist or is not readable")
exit(false)
end
tar_extract.rewind
# Loop over each entry and output file contents
tar_extract.each do |entry|
next if entry.directory?
# Oops! We don't check if the file is actually a symbolic link to a potentially sensitive file.
puts entry.read
end
```
#### Go
```golang
// printZipContents INSECURELY prints contents of files in a zip file.
func printZipContents(src string) error {
r, err := zip.OpenReader(src)
if err != nil {
return err
}
defer r.Close()
// Loop over each entry and output file contents
for _, f := range r.File {
if f.FileInfo().IsDir() {
continue
}
rc, err := f.Open()
if err != nil {
return err
}
defer rc.Close()
// Oops! We don't check if the file is actually a symbolic link to a potentially sensitive file.
buf, err := ioutil.ReadAll(rc)
if err != nil {
return err
}
fmt.Println(buf.String())
}
return nil
}
```
#### Best practices
Always check the type of the archive entry before reading the contents and ignore entries that are not plain files. If you absolutely must support symbolic links, ensure that they only point to files inside the archive and nowhere else.
##### Ruby
```ruby
# tar.gz extraction example with protection against symlink attacks.
STDERR.puts("archive file does not exist or is not readable")
exit(false)
end
tar_extract.rewind
# Loop over each entry and output file contents
tar_extract.each do |entry|
next if entry.directory?
# By skipping symbolic links entirely, we are sure they can't cause any trouble!
next if entry.symlink?
puts entry.read
end
```
##### Go
You are encouraged to use the secure archive utilities provided by [LabSec](https://gitlab.com/gitlab-com/gl-security/appsec/labsec) which will handle Zip Slip and symlink vulnerabilities for you. The LabSec utilities are also context aware which makes it possible to cancel or timeout extractions.
In case the LabSec utilities do not fit your needs, here is an example for extracting a zip file with protection against symlink attacks:
```golang
// printZipContents prints contents of files in a zip file with protection against symlink attacks.
func printZipContents(src string) error {
r, err := zip.OpenReader(src)
if err != nil {
return err
}
defer r.Close()
// Loop over each entry and output file contents
for _, f := range r.File {
if f.FileInfo().IsDir() {
continue
}
// By skipping all irregular file types (including symbolic links), we are sure they can't cause any trouble!
These types of bugs are often seen in environments which allow multi-threading and concurrency, like filesystems and distributed web applications; these are a type of race condition. TOCTOU also occurs when state is checked and stored, then after a period of time that state is relied on without re-checking its accuracy and/or validity.
### Examples
**Example 1:** you have a model which accepts a URL as input. When the model is created you verify that the URL's host resolves to a public IP address, to prevent attackers making internal network calls. But DNS records can change ([DNS rebinding](#server-side-request-forgery-ssrf)]). An attacker updates the DNS record to `127.0.0.1`, and when your code resolves those URL's host it results in sending a potentially malicious request to a server on the internal network. The property was valid at the "time of check", but invalid and malicious at "time of use".
GitLab-specific example can be found in [this issue](https://gitlab.com/gitlab-org/gitlab/-/issues/214401) where, although `Gitlab::UrlBlocker.validate!` was called, the returned value was not used. This made it vulnerable to TOCTOU bug and SSRF protection bypass through [DNS rebinding](#server-side-request-forgery-ssrf). The fix was to [use the validated IP address](https://gitlab.com/gitlab-org/gitlab/-/commit/7af8abd4df9a98f7a1ae7c4ec9840d0a7a8c684d).
**Example 2:** you have a feature which schedules jobs. When the user schedules the job, they have permission to do so. But imagine if, between the time they schedule the job and the time it is run, their permissions are restricted. Unless you re-check permissions at time of use, you could inadvertently allow unauthorized activity.
**Example 3:** you need to fetch a remote file, and perform a `HEAD` request to get and validate the content length and content type. When you subsequently make a `GET` request, though, the file delivered is a different size or different file type. (This is stretching the definition of TOCTOU, but things _have_ changed between time of check and time of use).
**Example 4:** you allow users to upvote a comment if they haven't already. The server is multi-threaded, and you aren't using transactions or an applicable database index. By repeatedly clicking upvote in quick succession a malicious user is able to add multiple upvotes: the requests arrive at the same time, the checks run in parallel and confirm that no upvote exists yet, and so each upvote is written to the database.
- Any other piece of information that can be used for authentication or authorization purposes.
This sensitive data must be handled carefully to avoid leaks which could lead to unauthorized access. If you have questions or need help with any of the following guidance, talk to the GitLab AppSec team on Slack (`#sec-appsec`).
### At rest
- Credentials must be encrypted while at rest (database or file) with `attr_encrypted`. See [issue #26243](https://gitlab.com/gitlab-org/gitlab/-/issues/26243) before using `attr_encrypted`.
- Store the encryption keys separately from the encrypted credentials with proper access control. For instance, store the keys in a vault, KMS, or file. Here is an [example](https://gitlab.com/gitlab-org/gitlab/-/blob/master/app/models/user.rb#L70-74) use of `attr_encrypted` for encryption with keys stored in separate access controlled file.
- When the intention is to only compare secrets, store only the salted hash of the secret instead of the encrypted value.
- Never commit credentials to repositories.
- The [Gitleaks Git hook](https://gitlab.com/gitlab-com/gl-security/security-research/gitleaks-endpoint-installer) is recommended for preventing credentials from being committed.
- Never log credentials under any circumstance. Issue [#353857](https://gitlab.com/gitlab-org/gitlab/-/issues/353857) is an example of credential leaks through log file.
- When credentials are required in a CI/CD job, use [masked variables](../ci/variables/index.md#mask-a-cicd-variable) to help prevent accidental exposure in the job logs. Be aware that when [debug logging](../ci/variables/index.md#debug-logging) is enabled, all masked CI/CD variables are visible in job logs. Also consider using [protected variables](../ci/variables/index.md#protected-cicd-variables) when possible so that sensitive CI/CD variables are only available to pipelines running on protected branches or protected tags.
- Proper scanners must be enabled depending on what data those credentials are protecting. See the [Application Security Inventory Policy](https://about.gitlab.com/handbook/engineering/security/security-engineering-and-research/application-security/inventory.html#policies) and our [Data Classification Standards](https://about.gitlab.com/handbook/engineering/security/data-classification-standard.html#data-classification-standards).
- To store and/or share credentials between teams, refer to [1Password for Teams](https://about.gitlab.com/handbook/security/#1password-for-teams) and follow [the 1Password Guidelines](https://about.gitlab.com/handbook/security/#1password-guidelines).
- If you need to share a secret with a team member, use 1Password. Do not share a secret over email, Slack, or other service on the Internet.
### In transit
- Use an encrypted channel like TLS to transmit credentials. See [our TLS minimum recommendation guidelines](#tls-minimum-recommended-version).
- Avoid including credentials as part of an HTTP response unless it is absolutely necessary as part of the workflow. For example, generating a PAT for users.
- Avoid sending credentials in URL parameters, as these can be more easily logged inadvertently during transit.
In the event of credential leak through an MR, issue, or any other medium, [reach out to SIRT team](https://about.gitlab.com/handbook/engineering/security/security-operations/sirt/#-engaging-sirt).
Serialization of active record models can leak sensitive attributes if they are not protected.
Using the [`prevent_from_serialization`](https://gitlab.com/gitlab-org/gitlab/-/blob/d7b85128c56cc3e669f72527d9f9acc36a1da95c/app/models/concerns/sensitive_serializable_hash.rb#L11)
method protects the attributes when the object is serialized with `serializable_hash`.
When an attribute is protected with `prevent_from_serialization`, it is not included with
`serializable_hash`, `to_json`, or `as_json`.
For more guidance on serialization:
- [Why using a serializer is important](https://gitlab.com/gitlab-org/gitlab/-/blob/master/app/serializers/README.md#why-using-a-serializer-is-important).
- Always use [Grape entities](../../ee/development/api_styleguide.md#entities) for the API.
To `serialize` an `ActiveRecord` column:
- You can use `app/serializers`.
- You cannot use `to_json / as_json`.
- You cannot use `serialize :some_colum`.
### Serialization example
The following is an example used for the [`TokenAuthenticatable`](https://gitlab.com/gitlab-org/gitlab/-/blob/9b15c6621588fce7a80e0438a39eeea2500fa8cd/app/models/concerns/token_authenticatable.rb#L30) class:
```ruby
prevent_from_serialization(*strategy.token_fields) if respond_to?(:prevent_from_serialization)
