CVE-2017-12976 in git-annex
Summary
by MITRE
git-annex before 6.20170818 allows remote attackers to execute arbitrary commands via an ssh URL with an initial dash character in the hostname, as demonstrated by an ssh://-eProxyCommand= URL, a related issue to CVE-2017-9800, CVE-2017-12836, CVE-2017-1000116, and CVE-2017-1000117.
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Analysis
by VulDB Data Team • 12/16/2022
The vulnerability identified as CVE-2017-12976 represents a critical command injection flaw in git-annex versions prior to 6.20170818. This security weakness specifically targets the handling of ssh URLs within the git-annex framework, where the software fails to properly sanitize user-provided hostname data. The vulnerability arises when an ssh URL contains an initial dash character in the hostname portion, creating a scenario where attacker-controlled input can be interpreted as command-line arguments by the underlying ssh client. This flaw enables remote attackers to execute arbitrary commands on systems running vulnerable versions of git-annex, making it a severe privilege escalation vector that can be exploited without authentication.
The technical mechanism behind this vulnerability involves the improper parsing of ssh URLs where the hostname begins with a dash character. When git-annex processes such URLs, it passes the hostname directly to the ssh client without adequate sanitization or validation. An attacker can craft a malicious URL such as ssh://-eProxyCommand= which exploits the fact that ssh interprets arguments beginning with dashes as command-line options. This allows attackers to inject arbitrary commands through the ProxyCommand option, effectively bypassing normal access controls and executing malicious code on the target system. The vulnerability is classified under CWE-78 as "Improper Neutralization of Special Elements used in an OS Command," which specifically addresses the dangerous practice of concatenating untrusted data into command execution contexts.
The operational impact of CVE-2017-12976 extends beyond simple command execution, as it represents a sophisticated attack vector that can be leveraged for complete system compromise. Attackers can utilize this vulnerability to establish persistent access, escalate privileges, or exfiltrate sensitive data from systems running vulnerable git-annex installations. The vulnerability is particularly concerning because it affects the core functionality of git-annex, which is widely used for distributed version control and data synchronization across multiple repositories. Systems that rely on git-annex for managing large datasets, especially in collaborative environments, become vulnerable to remote code execution attacks that can be triggered through various attack vectors including web interfaces, automated scripts, or malicious repository configurations. The vulnerability's relationship to other CVEs such as CVE-2017-9800, CVE-2017-12836, CVE-2017-1000116, and CVE-2017-1000117 demonstrates a pattern of command injection flaws in git-related software components, suggesting systematic weaknesses in how these tools handle external input.
Organizations should implement immediate mitigations including upgrading to git-annex version 6.20170818 or later, which contains patches addressing this specific vulnerability. Additionally, administrators should review and restrict access to git-annex repositories, particularly in environments where untrusted users might be able to influence repository configurations or URL specifications. Network-level controls such as firewall rules that restrict ssh access to known good hosts and monitoring for suspicious ssh URL patterns can provide additional defense-in-depth measures. The vulnerability aligns with ATT&CK technique T1059.001 for Command and Scripting Interpreter, specifically focusing on the execution of system commands through SSH protocols. Security teams should also consider implementing automated scanning tools to identify systems running vulnerable versions of git-annex and establish monitoring procedures to detect potential exploitation attempts through anomalous ssh command execution patterns. Regular security audits of version control infrastructure and proper input validation practices should be enforced to prevent similar vulnerabilities from emerging in other components of the software ecosystem.