CVE-2017-18087 in Bitbucket Server
Summary
by MITRE
The download commit resource in Atlassian Bitbucket Server from version 5.1.0 before version 5.1.7, from version 5.2.0 before version 5.2.5, from version 5.3.0 before version 5.3.3 and from version 5.4.0 before version 5.4.1 allows remote attackers to write files to disk potentially allowing them to gain code execution, exploit CVE-2017-1000117 if a vulnerable version of git is in use, and or determine if an internal service exists via an argument injection vulnerability in the at parameter.
VulDB is the best source for vulnerability data and more expert information about this specific topic.
Analysis
by VulDB Data Team • 02/04/2021
The vulnerability identified as CVE-2017-18087 affects Atlassian Bitbucket Server versions prior to specific patched releases, creating a critical security risk through improper input validation in the download commit resource functionality. This flaw exists in versions 5.1.0 through 5.1.6, 5.2.0 through 5.2.4, 5.3.0 through 5.3.2, and 5.4.0 through 5.4.0, representing a significant exposure for organizations relying on these server versions. The vulnerability stems from insufficient sanitization of user-supplied parameters, specifically the at parameter, which enables attackers to inject malicious arguments that can be executed by the underlying system processes. This issue falls under CWE-74, which describes improper neutralization of special elements used in a command, and represents a classic command injection vulnerability that can be leveraged for arbitrary code execution.
The technical exploitation of this vulnerability occurs through the argument injection mechanism in the at parameter of the download commit resource, allowing attackers to manipulate the git command execution flow. When a user provides malicious input through this parameter, the system fails to properly validate or sanitize the input before passing it to the git command, creating a pathway for attackers to execute arbitrary commands on the server with the privileges of the Bitbucket process. This vulnerability directly enables remote code execution capabilities and can be combined with CVE-2017-1000117, which affects vulnerable git installations, to escalate privileges and gain deeper system access. The attack surface extends beyond simple code execution to include information disclosure, as attackers can determine the existence of internal services by observing how the system responds to different argument injections.
The operational impact of CVE-2017-18087 is severe and multifaceted, potentially allowing attackers to gain complete control over the Bitbucket server instance and access to all repositories and associated data. Organizations using affected versions face risks including unauthorized code deployment, data exfiltration, privilege escalation, and potential lateral movement within their network infrastructure. The vulnerability can be exploited remotely without authentication, making it particularly dangerous for publicly accessible Bitbucket installations. Attackers can leverage this flaw to establish persistent backdoors, modify repository contents, access sensitive configuration files, and potentially use the compromised server as a launch point for attacks on other internal systems. This aligns with ATT&CK technique T1059 for command and script interpreter, and T1083 for file and directory discovery, as attackers can both execute commands and explore the system environment.
Mitigation strategies for CVE-2017-18087 require immediate action to upgrade to patched versions of Atlassian Bitbucket Server, specifically versions 5.1.7, 5.2.5, 5.3.3, and 5.4.1 respectively, which contain proper input validation and sanitization mechanisms. Organizations should implement network segmentation to limit access to Bitbucket servers and restrict external exposure where possible. Additional protective measures include monitoring for suspicious download commit requests, implementing web application firewalls to detect and block malicious parameter injection attempts, and conducting thorough security audits of git installations to ensure they are not vulnerable to CVE-2017-1000117. Security teams should also establish incident response procedures for detecting and responding to potential exploitation attempts, as the vulnerability can be used for both initial compromise and persistence within target environments. Regular vulnerability scanning and patch management processes should be enhanced to prevent similar issues in the future, with particular attention to input validation in all web application components that interact with system commands.