Background & Context

TeamCity is a build management and continuous integration server from JetBrains. It aims to to provide support for flexible workflows, collaboration and development practices within DevOps-centric teams. It exists in both self-hosted and cloud-based editions.

Vulnerability Summary

JetBrains TeamCity before 2023.05.4 contains a critical authentication bypass vulnerability.

Impact If Exploited

A remote attacker may be able to exploit this vulnerability to perform unauthorised remote execution of arbitrary code on impacted TeamCity Servers.

NOTE: This vulnerability has been reported by the CISA (America’s Cyber Defense Agency) to be known to be currently actively exploited in the wild as of 2023-10-05 onwards. Threat intelligence firm GreyNoise started seeing the first exploitation attempts on September 27, with a peak seen the following day. The company has seen attack attempts coming from 56 unique IP addresses as of October 1. Prioritisation should be given to remediation in any impacted environment.

Affected Product Versions

• JetBrains TeamCity prior to release 2023.05.4 (on-premises version only)

Remediation

Official Fix & Remediation Guidance

Customers of on-premises installations are advised to upgrade to the latest version of JetBrains TeamCity. Security patch plugins:

• https://download.jetbrains.com/teamcity/plugins/internal/CVE-2023-42793-fix-recent-versions.zip – TeamCity 2018.2 to 2023.05.3
• https://download.jetbrains.com/teamcity/plugins/internal/CVE-2023-42793-fix-2018-1.zip – TeamCity 8.0 to 2018.1]]

For TeamCity 2019.2 and later, the plugin can be enabled without restarting the TeamCity server. For versions older than 2019.2, a server restart is required after the plugin has been installed.

NOTE: due to active ongoing exploitation, customers who are unable to upgrade or apply a targeted fix for CVE-2023-42793 should consider taking the server offline until the vulnerability can be mitigated.

TeamCity Cloud customers do not need to take any action.

NOTE: Remediation of this vulnerability by patching to a specific version indicated may not be sufficient to secure the product against further vulnerabilities discovered in later versions, subsequent to the publication of this guidance. Unless contra-indicated, customers are therefore advised to always upgrade to the latest version of the product available.

Temporary Mitigation & Workarounds

(The vendor has not advised of any alternative temporary mitigation or workarounds)

NOTE: Caution should always be taken in applying any temporary mitigations listed. Mitigations are only recommended in cases where patches to remediate the vulnerability are not available, or cannot safely be applied to a given environment immediately. A given mitigation may not in all cases be recommended officially by the application vendor. The viability of any given temporary mitigation measure may vary, depending on server platform and existing configuration. Mitigations listed may incompletely remediate any given vulnerability. Configuration changes to implement listed mitigations may impact/disrupt required functionality within a given customer application. Care should therefore be taken to carefully analyse any listed mitigations for appropriateness to a given environment. Customers are advised to test any configuration changes prior to their being introduced into a production environment.

References:

• http://packetstormsecurity.com/files/174860/JetBrains-TeamCity-Unauthenticated-Remote-Code-Execution.html
• https://attackerkb.com/topics/1XEEEkGHzt/cve-2023-42793
• https://blog.jetbrains.com/teamcity/2023/09/cve-2023-42793-vulnerability-post-mortem/
• https://www.jetbrains.com/privacy-security/issues-fixed/
• https://www.rapid7.com/blog/post/2023/09/25/etr-cve-2023-42793-critical-authentication-bypass-in-jetbrains-teamcity-ci-cd-servers/
• https://www.securityweek.com/recently-patched-teamcity-vulnerability-exploited-to-hack-servers/
• https://viz.greynoise.io/tag/jetbrains-teamcity-authentication-bypass-attempt?days=10

Category: Arbitrary Code Execution

Detection

AppCheck has added a plugin to detect the flaw that will run as part of your standard scans.

About AppCheck

AppCheck is a software security vendor based in the UK, offering a leading security scanning platform that automates the discovery of security flaws within organisations websites, applications, network, and cloud infrastructure. AppCheck are authorized by the Common Vulnerabilities and Exposures (CVE) Program as a CVE Numbering Authority (CNA).