CVE-2012-3479 in Emacs
Summary
by MITRE
lisp/files.el in Emacs 23.2, 23.3, 23.4, and 24.1 automatically executes eval forms in local-variable sections when the enable-local-variables option is set to :safe, which allows user-assisted remote attackers to execute arbitrary Emacs Lisp code via a crafted file.
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Analysis
by VulDB Data Team • 12/31/2024
The vulnerability identified as CVE-2012-3479 represents a critical security flaw in the Emacs text editor that affects versions 23.2 through 24.1. This issue resides within the lisp/files.el component and specifically targets the handling of local variable sections in files. The vulnerability stems from the improper execution of eval forms when the enable-local-variables option is configured to :safe mode, creating a dangerous condition where malicious code can be automatically executed without proper user consent or awareness. This flaw fundamentally undermines the security model that Emacs employs to protect users from potentially harmful code execution during file processing operations.
The technical mechanism behind this vulnerability involves the automatic evaluation of Emacs Lisp code contained within local variable declarations when files are loaded into Emacs. When the enable-local-variables option is set to :safe, the system permits local variables to be processed but fails to properly sanitize or validate the content of these variables. Attackers can craft specially formatted files that contain malicious eval forms within their local variable sections, which are then automatically executed by Emacs when the file is opened. This behavior violates fundamental security principles by allowing arbitrary code execution without explicit user confirmation, effectively bypassing the intended security boundaries that should protect users from potentially harmful code.
The operational impact of this vulnerability extends beyond simple code execution, as it provides attackers with a sophisticated vector for remote code execution within the context of Emacs users. The vulnerability can be exploited through user-assisted remote attacks, meaning that an attacker only needs to convince a user to open a maliciously crafted file for the exploit to succeed. This makes the vulnerability particularly dangerous in environments where users frequently open files from untrusted sources, such as email attachments, web downloads, or shared network locations. The attack surface is broadened by the fact that many users may not be aware of the security implications of opening files from unknown sources, making this vulnerability particularly effective for social engineering attacks.
From a cybersecurity perspective, this vulnerability aligns with CWE-94, which describes the weakness of "Improper Control of Generation of Code ('Code Injection')" and demonstrates how improper handling of local variables can lead to arbitrary code execution. The vulnerability also maps to ATT&CK technique T1059.006, which covers "Command and Scripting Interpreter: Emacs", indicating that attackers can leverage this weakness to execute malicious code through the Emacs environment. The security implications are particularly severe because Emacs is widely used in development environments, system administration tasks, and academic settings where users may have elevated privileges or access to sensitive systems.
Mitigation strategies for this vulnerability include immediate patching of affected Emacs versions to the latest secure releases, which contain fixes that properly validate and sanitize local variable content before executing any eval forms. Administrators should also consider implementing restrictive file access policies that limit the types of files that can be automatically loaded into Emacs environments, particularly in shared or networked systems. Additionally, users should be educated about the risks of opening untrusted files in Emacs and should be trained to verify file sources before opening them. The configuration of enable-local-variables should be carefully reviewed and potentially set to more restrictive values, and users should be encouraged to avoid opening files from unknown sources, especially when working in environments where security is paramount. Organizations should also consider implementing automated security scanning tools that can detect potentially malicious file formats and prevent automatic execution of embedded code within text editors.