CVE-2017-1000115 in Mercurial
Summary
by MITRE
Mercurial prior to version 4.3 is vulnerable to a missing symlink check that can malicious repositories to modify files outside the repository
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Analysis
by VulDB Data Team • 12/30/2022
The vulnerability identified as CVE-2017-1000115 affects Mercurial version 4.3 and earlier, presenting a critical security flaw that stems from insufficient validation of symbolic links during repository operations. This weakness allows malicious repositories to manipulate files outside their designated boundaries, effectively bypassing the intended isolation mechanisms that should protect users from unauthorized file system modifications. The issue manifests when Mercurial processes repositories containing symbolic links that point to locations outside the repository directory structure, creating an attack vector that can be exploited by adversaries who control repository content.
The technical root cause of this vulnerability lies in Mercurial's failure to properly verify the target paths of symbolic links before performing file operations. When a repository contains a symlink that points outside the repository directory, the version control system does not adequately validate whether these links are safe to follow, enabling attackers to craft malicious repository structures that can traverse the file system and modify arbitrary files. This missing symlink check represents a classic case of inadequate input validation and path traversal protection, which aligns with common weakness patterns documented in CWE-367. The vulnerability essentially allows for a form of privilege escalation through repository manipulation, where the normal security boundaries of the repository environment are bypassed.
Operationally, this vulnerability presents significant risks to users who may unknowingly clone or pull from malicious repositories, particularly in collaborative environments or when working with untrusted code sources. Attackers can construct repositories with carefully crafted symbolic links that, when processed by vulnerable Mercurial versions, can overwrite system files, modify configuration settings, or even inject malicious code into critical components of the operating system. The impact extends beyond simple file modification to potentially compromise the integrity of the entire system, as attackers can leverage this vulnerability to gain persistent access or disrupt normal system operations. This type of vulnerability is particularly dangerous in automated build environments or continuous integration systems where repository cloning and merging operations occur frequently.
The security implications of CVE-2017-1000115 align with tactics described in the MITRE ATT&CK framework under the 'Persistence' and 'Privilege Escalation' domains, as attackers can establish footholds within systems through repository manipulation. Organizations using Mercurial should consider this vulnerability as part of their broader security posture assessment, particularly in environments where repository access controls are not strictly enforced. The vulnerability also demonstrates the importance of proper sandboxing and containment mechanisms in version control systems, as it shows how seemingly isolated operations can be used to escape confinement boundaries. Remediation efforts should focus on upgrading to Mercurial version 4.3 or later, where the symlink validation has been properly implemented, along with implementing additional security measures such as repository access controls and automated scanning for suspicious repository content.