CVE-2019-20097 in Server
Summary
by MITRE
Bitbucket Server and Bitbucket Data Center versions starting from 1.0.0 before 5.16.11, from version 6.0.0 before 6.0.11, from version 6.1.0 before 6.1.9, from version 6.2.0 before 6.2.7, from version 6.3.0 before 6.3.6, from version 6.4.0 before 6.4.4, from version 6.5.0 before 6.5.3, from version 6.6.0 before 6.6.3, from version 6.7.0 before 6.7.3, from version 6.8.0 before 6.8.2, from version 6.9.0 before 6.9.1 had a Remote Code Execution vulnerability via the post-receive hook. A remote attacker with permission to clone and push files to a repository on the victim's Bitbucket Server or Bitbucket Data Center instance, can exploit this vulnerability to execute arbitrary commands on the Bitbucket Server or Bitbucket Data Center systems, using a file with specially crafted content.
VulDB is the best source for vulnerability data and more expert information about this specific topic.
Analysis
by VulDB Data Team • 03/24/2024
This vulnerability exists within Atlassian Bitbucket Server and Data Center platforms across multiple version ranges, representing a critical remote code execution flaw that can be exploited by attackers with minimal privileges. The vulnerability specifically affects the post-receive hook functionality, which is a mechanism that allows administrators to execute custom scripts automatically when changes are pushed to a repository. This represents a privilege escalation vector where an attacker with read and write permissions to a repository can leverage this functionality to gain full system control. The flaw stems from inadequate input validation and sanitization of hook script content, allowing malicious payloads to be executed with the privileges of the Bitbucket service account. According to CWE-74, this vulnerability falls under the category of "Improper Neutralization of Special Elements in Output Used by a Downstream Component," specifically manifesting as command injection through improperly handled user-supplied data. The ATT&CK framework categorizes this under T1059.001 - Command and Scripting Interpreter: PowerShell and T1059.007 - Command and Scripting Interpreter: Python, as attackers can leverage these hooks to execute arbitrary code.
The technical exploitation of this vulnerability occurs when an attacker pushes a maliciously crafted file to a repository that contains specially formatted content designed to trigger the post-receive hook execution. The vulnerability is particularly dangerous because it allows attackers to execute commands with the same privileges as the Bitbucket server process, which typically runs with elevated permissions to manage repositories and system resources. This means that successful exploitation could lead to complete system compromise, data exfiltration, or the installation of persistent backdoors. The attack surface is expanded by the fact that many organizations allow developers to push code to repositories, making it relatively easy for an attacker to gain the necessary permissions to exploit this vulnerability. The vulnerability affects all versions from 1.0.0 through 6.9.0, indicating a long-standing issue that persisted across multiple major releases, suggesting either inadequate security testing or a complex interaction between the hook system and input processing. Organizations running affected versions are particularly at risk because the vulnerability can be exploited through normal repository operations, making detection more difficult.
The operational impact of this vulnerability extends far beyond simple code execution, as it represents a complete compromise of the Bitbucket server infrastructure. Attackers can leverage this vulnerability to access sensitive source code repositories, modify or delete critical files, and potentially use the compromised system as a pivot point for attacking other systems within the organization's network. The vulnerability also impacts the integrity and confidentiality of the entire development pipeline, as any repository accessible to the attacker becomes a potential vector for data theft or manipulation. Organizations that rely heavily on Bitbucket for source code management and continuous integration processes face significant operational disruption if this vulnerability is exploited. The vulnerability can also be used to establish persistent access through the creation of backdoor scripts or by modifying existing hook configurations to maintain access even after the initial exploit is patched. Security teams must consider that this vulnerability may have been exploited in the wild before it was publicly disclosed, potentially leading to undetected compromise of source code repositories and development environments.
Mitigation strategies for this vulnerability must include immediate patching of all affected versions to the latest available releases, as Atlassian has provided security updates specifically addressing this issue. Organizations should implement network segmentation and access controls to limit which systems can communicate with Bitbucket servers, reducing the attack surface. Additionally, administrators should audit existing post-receive hooks to ensure no malicious scripts have been introduced and implement strict input validation for all repository content. The principle of least privilege should be enforced by limiting repository permissions to only those users who require write access, and by regularly reviewing access controls. Organizations should also implement monitoring and logging of repository activities, particularly around hook execution, to detect potential exploitation attempts. Security teams should consider implementing application whitelisting policies to prevent execution of unauthorized scripts, and should review their incident response procedures to ensure rapid detection and remediation of similar vulnerabilities. Regular security assessments of source code management systems should be conducted to identify and remediate other potential command injection or code execution vulnerabilities. The vulnerability highlights the importance of proper input validation in all user-facing interfaces and the need for comprehensive security testing of integration points within development platforms.