CVE-2017-12836 in CVS
Summary
by MITRE
CVS 1.12.x, when configured to use SSH for remote repositories, might allow remote attackers to execute arbitrary code via a repository URL with a crafted hostname, as demonstrated by "-oProxyCommand=id;localhost:/bar."
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Analysis
by VulDB Data Team • 12/16/2022
The vulnerability identified as CVE-2017-12836 represents a critical remote code execution flaw within CVS (Concurrent Versions System) version 1.12.x when configured to utilize SSH for remote repository access. This issue stems from insufficient input validation and improper handling of hostname parameters within repository URLs, creating a dangerous attack vector that adversaries can exploit to gain unauthorized system access. The vulnerability specifically manifests when CVS processes repository URLs containing crafted hostnames that leverage SSH's ProxyCommand functionality, allowing malicious commands to be executed within the context of the CVS process.
The technical exploitation mechanism relies on SSH's ProxyCommand directive which enables users to specify a command to be executed on the local machine to establish a connection to a remote host. In this case, the crafted URL "-oProxyCommand=id;localhost:/bar" demonstrates how an attacker can inject arbitrary commands through the hostname parameter. When CVS processes this malformed URL, it passes the entire string to SSH without proper sanitization, effectively executing the command "id" as part of the SSH connection establishment process. This represents a classic command injection vulnerability where user-controllable input directly influences the execution of system commands, violating fundamental security principles of input validation and command construction.
The operational impact of this vulnerability extends beyond simple code execution to encompass full system compromise capabilities. An attacker with remote access to a system running CVS with SSH configuration can execute arbitrary commands with the privileges of the CVS process, potentially leading to complete system takeover. The vulnerability affects systems where CVS is configured to use SSH for repository access, making it particularly dangerous in enterprise environments where version control systems often run with elevated privileges. The attack requires minimal sophistication to execute, as demonstrated by the simple command injection pattern, making it an attractive target for automated exploitation tools and less skilled attackers.
This vulnerability aligns with CWE-78, which specifically addresses improper neutralization of special elements used in OS commands, and demonstrates the dangerous intersection of configuration management and command execution. The flaw also relates to ATT&CK technique T1059.001, which covers command and scripting interpreter execution through shell commands, highlighting how this vulnerability enables adversaries to leverage legitimate system tools for malicious purposes. Organizations using CVS in production environments should immediately implement mitigations including updating to patched versions, disabling SSH-based repository access where possible, and implementing strict input validation for repository URLs. Network segmentation and access controls should be enforced to limit exposure, while monitoring systems should be configured to detect suspicious command execution patterns and unusual SSH connection behaviors. The vulnerability underscores the critical importance of proper input sanitization in security-sensitive applications and the potential consequences of inadequate validation of user-provided data in system integration points.