CloudBees Security Advisory 2024-01-24

This advisory announces vulnerabilities in CloudBees CI and Jenkins

Arbitrary file read vulnerability through the CLI can lead to RCE

SECURITY-3314 / CVE-2024-23897
Severity (CVSS): Critical
Description:

Jenkins has a built-in command line interface (CLI) to access Jenkins from a script or shell environment.

Jenkins uses the args4j library to parse command arguments and options on the Jenkins controller when processing CLI commands. This command parser has a feature that replaces an @ character followed by a file path in an argument with the file’s contents (expandAtFiles). This feature is enabled by default and CloudBees CI 2.426.2.2 and earlier, Jenkins 2.441 and earlier, LTS 2.426.2 and earlier does not disable it.

This allows attackers to read arbitrary files on the Jenkins controller file system using the default character encoding of the Jenkins controller process.

  • Attackers with Overall/Read permission can read entire files.

  • Attackers without Overall/Read permission can read the first few lines of files. The number of lines that can be read depends on available CLI commands. As of publication of this advisory, the Jenkins security team has found ways to read the first three lines of files in recent releases of Jenkins without having any plugins installed, and has not identified any plugins that would increase this line count.

Binary files containing cryptographic keys used for various Jenkins features can also be read, with some limitations (see note on Limitations of reading binary files below). As of publication, the Jenkins security team has confirmed the following possible attacks in addition to reading contents of all files with a known file path. All of them leverage attackers' ability to obtain cryptographic keys from binary files, and are therefore only applicable to instances where that is feasible.

This list is not definitive. Further attacks likely exist, including ones that do not need attackers to obtain cryptographic keys from binary files.

  • Remote code execution via Resource Root URLs (Variant 1)
    Exploitation requires that all of the following conditions are met:

    • The "Resource Root URL" functionality is enabled (see documentation).

    • The CLI WebSocket endpoint is accessible. This requires that Jenkins is running on a version of Jetty for which Jenkins supports WebSockets. This is the case when using the provided native installers, packages, or the Docker containers, as well as when running Jenkins with the command java -jar jenkins.war. Additionally, reverse proxies may not allow WebSocket requests if improperly configured.

    • Attackers can retrieve binary secrets (see note on Limitations of reading binary files below).

    • Attackers know, or can guess, the user name of any user with Overall/Read permission.

  • Remote code execution via Resource Root URLs (Variant 2)
    Exploitation requires that all of the following conditions are met:

    • The "Resource Root URL" functionality is enabled (see documentation).

    • Attackers can retrieve binary secrets (see note on Limitations of reading binary files below).

    • The attacker needs an API token for a (non-anonymous) user account. It is not necessary for this user account to (still) have Overall/Read permission.

  • Remote code execution via "Remember me" cookie
    Forging a "Remember me" cookie allows attackers to log in to Jenkins using a web browser, thereby gaining access to the Script Console if they forge a cookie for an administrator account. Exploitation requires that all of the following conditions are met:

    • The "Remember me" feature is enabled (the default).

    • Attackers can retrieve binary secrets (see note on Limitations of reading binary files below).

    • Attackers have Overall/Read permission to be able to read content in files beyond the first few lines.

  • Remote code execution via stored cross-site scripting (XSS) attacks through build logs
    Forging serialized console note objects allows implementing XSS attacks by injecting arbitrary HTML and JavaScript into build logs. This attack bypasses the protections added for SECURITY-382 in the 2017-02-01 security advisory. Exploitation requires that all of the following conditions are met:

    • Attackers can control build log output (e.g., through pull requests).

    • Attackers can retrieve binary secrets (see note on Limitations of reading binary files below).

  • Remote code execution via CSRF protection bypass
    Forged CSRF tokens ("crumbs") can be used to implement CSRF attacks by sending POST requests with a valid crumb. Exploitation requires that all of the following conditions are met:

  • Decrypt secrets stored in Jenkins
    Jenkins typically uses secrets to access other systems, like SCMs, external user directories for security realms, cloud providers, deployment targets, etc. Exploitation requires that all of the following conditions are met:

    • Attackers can retrieve binary secrets (see note on Limitations of reading binary files below).

    • Attackers have access to encrypted secrets. This may require Overall/Read permission, to be able to read content in files beyond the first few lines, but there are other possible sources, like JENKINS_HOME backups even if they exclude secrets/, or Configuration as Code YAML files.

  • Delete any item in Jenkins
    Exploitation requires that all of the following conditions are met:

    • The "Resource Root URL" functionality is enabled (see documentation).

    • Attackers can retrieve binary secrets (see note on Limitations of reading binary files below).

    • Attackers know, or can guess, the user name of any user with Overall/Read permission.

  • Download a Java heap dump of the Jenkins controller process or any agent process
    Exploitation requires that all of the following conditions are met:

    • The "Resource Root URL" functionality is enabled (see documentation).

    • Attackers can retrieve binary secrets (see note on Limitations of reading binary files below).

    • Attackers know, or can guess, the user name of any user with Overall/Read permission.

    • The Jenkins controller or agent process is running on a Java runtime that allows the creation of heap dump files without .hprof file extension. Due to JENKINS-72579 the affected feature does not work by default on recent releases of OpenJDK/HotSpot based JVMs.

Impact of reading arbitrary files

We have previously considered arbitrary file read vulnerabilities to only have an impact on confidentiality. As a result of the report provided by Yaniv Nizry (SonarSource) and the additional research done by the Jenkins security team resulting in the list above, future vulnerabilities of this kind will likewise be considered to have a high score across all impact metrics (confidentiality, integrity, and availability).

Limitations for reading binary files

While files containing binary data can be read, the affected feature attempts to read them as strings using the controller process’s default character encoding. This is likely to result in some bytes not being read successfully and being replaced with a placeholder value. Which bytes can or cannot be read depends on this character encoding. For example, attempting to read random binary data using UTF-8, roughly half of all bytes will be replaced with a placeholder for an illegal value. For 32 byte random binary secrets, as commonly used in Jenkins for HMAC-SHA256, this would require attackers to correctly guess on average 16 bytes, which is infeasible. In contrast, with the encoding Windows-1252, only 5 out of 256 possible values are illegal and would be replaced with a placeholder. This is a significantly lower number of bytes to guess in a binary secret on average, as well as fewer possible options for each byte.

CloudBees usage data collected through the Jenkins Health Advisor service indicates that more than 98% of CloudBees CI instances use UTF-8 as default character encoding. Almost all instances running on Linux and Mac OS X use UTF-8. Instances on Windows are more likely than not to use a character set that makes it feasible to implement exploits involving reading binary files (like Windows-1252).

To determine whether you’re likely affected by the most severe impacts described above, check the value of the file.encoding system property in Manage Jenkins » System Information.

While it is unlikely that randomly generated keys use significantly fewer than average of the byte values that cannot be read using a character encoding like UTF-8, it isn’t impossible. Therefore administrators should update Jenkins in a timely manner, regardless of the value of file.encoding.

Fix Description:
CloudBees CI 2.426.3.3, Jenkins 2.442, LTS 2.426.3 disables the command parser feature that replaces an @ character followed by a file path in an argument with the file’s contents for CLI commands.

In case of problems with this fix, disable this change by setting the Java system property hudson.cli.CLICommand.allowAtSyntax to true. Doing this is strongly discouraged on any network accessible by users who are not Jenkins administrators.

Workaround:
Disabling access to the CLI is expected to prevent exploitation completely. Doing so is strongly recommended to administrators unable to immediately update to CloudBees CI 2.426.3.3, Jenkins 2.442 or LTS 2.426.3. Applying this workaround does not require a Jenkins restart. For instructions, see Disable Jenkins CLI (for CloudBees Operations Center) and Disable Jenkins CLI across all controllers.

Disabling the CLI is only intended as a short-term workaround, even if you do not use the CLI.

Cross-site WebSocket hijacking vulnerability in the CLI

SECURITY-3315 / CVE-2024-23898
Severity (CVSS): High
Description:

Jenkins has a built-in command line interface (CLI) to access Jenkins from a script or shell environment. Since CloudBees CI 2.222.1.1, Jenkins 2.217 and LTS 2.222.1, one of the ways to communicate with the CLI is through a WebSocket endpoint. This endpoint relies on the default Jenkins web request authentication functionality, like HTTP Basic authentication with API tokens, or session cookies. This endpoint is enabled when running on a version of Jetty for which Jenkins supports WebSockets. This is the case when using the provided native installers, packages, or the Docker containers, as well as when running Jenkins with the command java -jar jenkins.war.

CloudBees CI 2.222.1.1 through 2.426.2.2 (both inclusive), Jenkins 2.217 through 2.441 (both inclusive), LTS 2.222.1 through 2.426.2 (both inclusive) does not perform origin validation of requests made through the CLI WebSocket endpoint, resulting in a cross-site WebSocket hijacking (CSWSH) vulnerability.

Additionally, Jenkins does not set an explicit SameSite attribute for session cookies. This can allow cross-site requests to make use of the session cookie, i.e., those requests are sent with the logged-in user’s authentication.

In recent releases of Google Chrome and Microsoft Edge the default behavior is for the SameSite cookie attribute to be considered Lax if not explicitly set. This results in no session cookie being sent with a cross-site request to the WebSocket endpoint, resulting in CLI use as the anonymous user. Mozilla Firefox has an option for this behavior, but it is disabled by default as of publication of this advisory. See this browser compatibility table (row labeled Defaults to Lax) for details.

This vulnerability allows attackers to execute CLI commands on the Jenkins controller. The impact depends on the permissions of the anonymous user and/or the browser(s) used by the victim(s) of the CSWSH attack:

  • The anonymous user has no permissions and Jenkins users use web browsers with SameSite cookie attribute Lax as default
    Attackers can execute the who-am-i CLI command, obtaining limited information about the anonymous user in Jenkins. This mostly allows exploiting SECURITY-3314 and reading the first few lines of files on the Jenkins controller. See that issue for more information about the potential impact.

  • The anonymous user has permissions
    This is the case with an authorization strategy like "Anyone can do anything", or when the anonymous user has explicitly been granted additional permissions. Attackers can execute the CLI commands that these permissions allow using, up to and including Groovy scripting capabilities (groovy and groovysh commands) resulting in arbitrary code execution. If the anonymous user has (only) Overall/Read permission, attackers can obtain the full contents of files by exploiting SECURITY-3314 as described in that issue.

  • Jenkins users use web browsers with SameSite cookie attribute Lax not being the default
    The session and/or "Remember me" cookie will be sent with the cross-site request, and the user will be authenticated. Attackers can execute the CLI commands that the victim’s permissions allow using, up to and including Groovy scripting capabilities (groovy and groovysh commands) in case of a Jenkins administrator, resulting in arbitrary code execution.

Fix Description:
CloudBees 2.426.3.3, Jenkins 2.442, LTS 2.426.3 performs origin validation of requests made through the CLI WebSocket endpoint.

In case of problems with this fix, disable this change by setting the Java system property hudson.cli.CLIAction.ALLOW_WEBSOCKET to true.

Workaround:
Some workarounds are available to mitigate some or all of the impact if you are unable to immediately upgrade to CloudBees 2.426.3.3, Jenkins 2.442, LTS 2.426.3:

  • Disable CLI access
    Disabling access to the CLI will prevent exploitation completely and is the recommended workaround for administrators unable to immediately update. Applying this workaround does not require a Jenkins restart. For instructions, see Disable Jenkins CLI (for CloudBees Operations Center) and Disable Jenkins CLI across all controllers.

  • Prevent WebSocket access using a reverse proxy
    If Jenkins is accessible only through a reverse proxy, configure that proxy to prevent access to the CLI via WebSocket by not upgrading requests.

Note: Administrators of Jenkins instances accessed through a reverse proxy can follow the instructions below to test whether WebSocket endpoints can be reached. These instructions assume that the reverse proxy is not set up to support only selected WebSocket endpoints (e.g., only the CLI).

  1. Log in to Jenkins as a user with Overall/Administer permission.

  2. Open your web browser’s developer tools while viewing the Jenkins dashboard.

  3. On the

    Console

    tab, paste the following script:

new WebSocket(document.location.toString().replace('http', 'ws') + 'wsecho/')

On the Network tab, if the wsecho/ request resulted in a 101 Switching Protocols response, WebSocket endpoints can be accessed. A 400 Bad Request response, or lack of response (in Google Chrome), indicates that WebSocket endpoints cannot be accessed. A 403 Forbidden response indicates that the necessary Overall/Administer permission is missing.

These steps have been validated in Google Chrome, Mozilla Firefox, and Apple Safari.

Arbitrary file read vulnerability in Git server Plugin can lead to RCE

SECURITY-3319 / CVE-2024-23899
Severity (CVSS): High
Affected plugin: git-server
Description:

Git server Plugin uses the args4j library to parse command arguments and options on the Jenkins controller when processing Git commands received via SSH. This command parser has a feature that replaces an @ character followed by a file path in an argument with the file’s contents (expandAtFiles). This feature is enabled by default and Git server Plugin 99.va_0826a_b_cdfa_d and earlier does not disable it.

This allows attackers with Overall/Read permission to read the first two lines of arbitrary files on the Jenkins controller file system using the default character encoding of the Jenkins controller process.

See SECURITY-3314 for further information about the potential impact of being able to read files on the Jenkins controller, as well as the limitations for reading binary files (see note on Limitations of reading binary files above) Note that for this issue, unlike SECURITY-3314, attackers need Overall/Read permission.

Fix Description:
Git server Plugin 99.101.v720e86326c09 disables the command parser feature that replaces an @ character followed by a file path in an argument with the file’s contents for CLI commands.

Workaround:
Navigate to Manage Jenkins » Security and ensure that the SSHD Port setting in the SSH Server section is set to Disable. This disables access to Git repositories hosted by Jenkins (and the Jenkins CLI) via SSH.

Path traversal vulnerability in Matrix Project Plugin

SECURITY-3289 / CVE-2024-23900
Severity (CVSS): Medium
Affected plugin: matrix-project
Description:

Matrix Project Plugin 822.v01b_8c85d16d2 and earlier does not sanitize user-defined axis names of multi-configuration projects submitted through the config.xml REST API endpoint.

This allows attackers with Item/Configure permission to create or replace any config.xml file on the Jenkins controller file system with content not controllable by the attackers.

Matrix Project Plugin 822.824.v14451b_c0fd42 sanitizes user-defined axis names of Multi-configuration project.

Shared projects are unconditionally discovered by GitLab Branch Source Plugin

SECURITY-3040 / CVE-2024-23901
Severity (CVSS): Medium
Affected plugin: gitlab-branch-source
Description:

GitLab allows sharing a project with another group.

GitLab Branch Source Plugin 684.vea_fa_7c1e2fe3 and earlier unconditionally discovers projects that are shared with the configured owner group.

This allows attackers to configure and share a project, resulting in a crafted Pipeline being built by Jenkins after the next scan of the group’s projects.

In GitLab Branch Source Plugin 688.v5fa_356ee8520, the default strategy for discovering projects does not discover projects shared with the configured owner group. To discover projects shared with the configured owner group, use the new trait "Discover shared projects".

After updating, any shared project that has already been discovered will be removed unless the new trait is added to the organization folder configuration before running a scan.

CSRF vulnerability in GitLab Branch Source Plugin

SECURITY-3251 / CVE-2024-23902
Severity (CVSS): Medium
Affected plugin: gitlab-branch-source
Description:

GitLab Branch Source Plugin 684.vea_fa_7c1e2fe3 and earlier does not require POST requests for a form validation endpoint, resulting in a cross-site request forgery (CSRF) vulnerability.

This vulnerability allows attackers to connect to an attacker-specified URL.

GitLab Branch Source Plugin 688.v5fa_356ee8520 requires POST requests for the affected form validation endpoint.

Non-constant time webhook token comparison in GitLab Branch Source Plugin

SECURITY-2871 / CVE-2024-23903
Severity (CVSS): Low
Affected plugin: gitlab-branch-source
Description:

GitLab Branch Source Plugin 684.vea_fa_7c1e2fe3 and earlier does not use a constant-time comparison function when checking whether the provided and expected webhook token are equal.

This could potentially allow attackers to use statistical methods to obtain a valid webhook token.

GitLab Branch Source Plugin 688.v5fa_356ee8520 uses a constant-time comparison function when validating the webhook token.

Stored XSS vulnerability in Qualys Policy Compliance Scanning Connector Plugin

SECURITY-3006 / CVE-2023-6148
Severity (CVSS): High
Affected plugin: qualys-pc
Description:

Qualys Policy Compliance Scanning Connector Plugin 1.0.5 and earlier does not escape Qualys API responses displayed on the job configuration page.

This results in a stored cross-site scripting (XSS) vulnerability exploitable by attackers able to configure jobs.

Qualys Policy Compliance Scanning Connector Plugin 1.0.6 escapes Qualys API responses displayed on the job configuration page.

XXE vulnerability in Qualys Policy Compliance Scanning Connector Plugin

SECURITY-3005 / CVE-2023-6147
Severity (CVSS): High
Affected plugin: qualys-pc
Description:

Qualys Policy Compliance Scanning Connector Plugin 1.0.5 and earlier does not configure its XML parser to prevent XML external entity (XXE) attacks.

This allows attackers able to configure jobs to have Jenkins parse a crafted HTTP response with XML data that uses external entities for extraction of secrets from the Jenkins controller or server-side request forgery.

Qualys Policy Compliance Scanning Connector Plugin 1.0.6 disables external entity resolution for its XML parser.

Incorrect permission checks in Qualys Policy Compliance Scanning Connector Plugin allow capturing credentials

SECURITY-3007 / CVE pending
Severity (CVSS): Medium
Affected plugin: qualys-pc
Description:

Qualys Policy Compliance Scanning Connector Plugin 1.0.5 and earlier does not correctly perform permission checks in several HTTP endpoints.

This allows attackers with global Item/Configure permission (while lacking Item/Configure permission on any particular job) to connect to an attacker-specified URL using attacker-specified credentials IDs obtained through another method, capturing credentials stored in Jenkins.

Qualys Policy Compliance Scanning Connector Plugin 1.0.6 requires the appropriate permissions for the affected HTTP endpoints.

Content-Security-Policy protection for user content disabled by Red Hat Dependency Analytics Plugin

SECURITY-3322 / CVE-2024-23905
Severity (CVSS): High
Affected plugin: redhat-dependency-analytics
Description:

Jenkins sets the Content-Security-Policy header to static files served by Jenkins (specifically DirectoryBrowserSupport), such as workspaces, /userContent, or archived artifacts, unless a Resource Root URL is specified.

Red Hat Dependency Analytics Plugin 0.7.1 and earlier globally disables the Content-Security-Policy header for static files served by Jenkins whenever the 'Invoke Red Hat Dependency Analytics (RHDA)' build step is executed. This allows cross-site scripting (XSS) attacks by users with the ability to control files in workspaces, archived artifacts, etc.

Jenkins instances with Resource Root URL configured are unaffected.

Red Hat Dependency Analytics Plugin 0.9.0 does not disable the Content-Security-Policy header for static files served by Jenkins anymore.

Arbitrary file read vulnerability in Log Command Plugin

SECURITY-3334 / CVE-2024-23904
Severity (CVSS): High
Affected plugin: log-command
Description:

Log Command Plugin uses the args4j library to parse command arguments and options on the Jenkins controller when processing commands received via instant messaging platforms such as IRC or Jabber. This command parser has a feature that replaces an @ character followed by a file path in an argument with the file’s contents (expandAtFiles). This feature is enabled by default and Log Command Plugin 1.0.2 and earlier does not disable it.

This allows unauthenticated attackers to read the first line of arbitrary files on the Jenkins controller file system using the default character encoding of the Jenkins controller process.

See SECURITY-3314 for further information about the potential impact of being able to read files on the Jenkins controller, as well as the limitations for reading binary files (see note on Limitations of reading binary files above).

The severity of this issue assumes attackers have no access to Jenkins other than via instant messaging platforms. If attackers can access Jenkins (even lacking Overall/Read permission), the severity is critical.

As of publication of this advisory, there is no fix. Learn why we announce this.

XXE in Infradna-Backup Plugin

BEE-42748
Severity (CVSS): Medium
Affected plugin: infradna-backup
Description:

CloudBees Backup (Infradna-backup) 3.38.71 and earlier does not configure its XML parser to prevent XML external entity (XXE) attacks.

This allows attackers able to control Backup file contents to have Jenkins parse a crafted XML document that uses external entities for extraction of secrets from the Jenkins controller or server-side request forgery.

CloudBees Backup (Infradna-backup) 3.38.72 fixes the issue.

Severity

Fix

  • CloudBees Traditional Platforms should be upgraded to 2.426.3.3

  • CloudBees Cloud Platforms should be upgraded to 2.426.3.3