CVE-2007-5795 in Emacs
Summary
by MITRE
The hack-local-variables function in Emacs before 22.2, when enable-local-variables is set to :safe, does not properly search lists of unsafe or risky variables, which might allow user-assisted attackers to bypass intended restrictions and modify critical program variables via a file containing a Local variables declaration.
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Analysis
by VulDB Data Team • 01/12/2025
The vulnerability described in CVE-2007-5795 represents a significant security flaw in the Emacs text editor that existed prior to version 22.2. This issue specifically targets the hack-local-variables function which is responsible for handling local variable declarations within Emacs files. When the enable-local-variables setting is configured to :safe mode, the system should theoretically restrict modifications to potentially dangerous variables while allowing safe ones. However, the implementation contained a critical oversight in how it processes lists of variables, creating a bypass mechanism that attackers could exploit.
The technical flaw stems from improper validation of local variable declarations within Emacs files. When enable-local-variables is set to :safe, Emacs should only permit modifications to a predefined list of safe variables while blocking access to risky ones. The vulnerability occurs because the hack-local-variables function fails to properly iterate through or validate the complete list of potentially unsafe variables, allowing attackers to include malicious variable declarations in local variable sections of files. This creates a scenario where an attacker can craft a file containing carefully constructed local variable declarations that circumvent the intended security restrictions.
The operational impact of this vulnerability is substantial as it allows user-assisted attackers to gain unauthorized access to critical program variables within the Emacs environment. An attacker could craft a malicious file with local variable declarations that would be processed by Emacs when the file is opened, potentially allowing modification of internal Emacs variables that control program behavior. This could lead to privilege escalation, code execution, or other malicious activities depending on how the modified variables are utilized within the Emacs codebase. The vulnerability particularly affects systems where users might open untrusted files or when Emacs is configured to automatically process local variables in files.
This vulnerability maps to CWE-264, which covers permissions, privileges, and access controls, specifically focusing on improper access control mechanisms within software applications. The flaw demonstrates poor input validation and insufficient sanitization of user-provided data within the local variable processing pipeline. From an ATT&CK perspective, this vulnerability aligns with T1059.006 for execution through scripting and T1548.001 for privilege escalation through modification of program execution. The attack surface is particularly concerning in environments where users regularly open files from untrusted sources or where Emacs is used in automated processing workflows. The vulnerability highlights the importance of proper variable validation and the need for comprehensive security testing of configuration handling mechanisms.
The recommended mitigations for this vulnerability include upgrading to Emacs version 22.2 or later where the issue has been resolved through proper list validation in the hack-local-variables function. Administrators should also consider implementing additional security measures such as disabling enable-local-variables entirely for untrusted environments or configuring more restrictive local variable policies. Regular security audits of configuration handling code should be performed to identify similar validation flaws. Organizations should also consider implementing file access controls and sandboxing mechanisms to limit the potential impact of such vulnerabilities. The fix in the patched version ensures that all variables in local declarations are properly validated against the safe variable list, preventing bypass attempts through malformed or crafted variable declarations.