CVE-2014-3423 in Emacs
Summary
by MITRE
lisp/net/browse-url.el in GNU Emacs 24.3 and earlier allows local users to overwrite arbitrary files via a symlink attack on a /tmp/Mosaic.##### temporary file.
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Analysis
by VulDB Data Team • 06/20/2021
The vulnerability described in CVE-2014-3423 represents a critical security flaw in GNU Emacs version 24.3 and earlier, specifically within the lisp/net/browse-url.el component. This issue enables local attackers to perform file overwriting operations through a carefully crafted symbolic link attack against a temporary file located at /tmp/Mosaic. The vulnerability stems from improper handling of temporary files during URL browsing operations, creating a window of opportunity for privilege escalation and data manipulation. The attack vector exploits the predictable naming convention of temporary files and the lack of proper security checks when creating or accessing these files. This flaw is particularly dangerous because it allows an attacker with local access to potentially overwrite any file on the system with arbitrary content, depending on the permissions and context of the target file.
The technical implementation of this vulnerability follows a classic symlink attack pattern where the malicious user creates a symbolic link pointing to a target file before the vulnerable application creates its own temporary file. In this case, the browse-url functionality in GNU Emacs creates temporary files without sufficient security measures to prevent symlink attacks, specifically targeting the /tmp/Mosaic temporary file location. When the application attempts to create or access this temporary file, it follows the symbolic link and writes data to the target file instead of the intended temporary location. This behavior violates fundamental security principles regarding temporary file creation and access control. The vulnerability is categorized under CWE-367, which addresses Time-of-Check to Time-of-Use (TOCTOU) race conditions, where the application's security decision is made at one point in time but the actual operation occurs at a different time, allowing attackers to manipulate the environment between these checks.
The operational impact of CVE-2014-3423 extends beyond simple file overwriting capabilities and can result in significant system compromise depending on the context in which GNU Emacs is used. When local users can overwrite arbitrary files, they may target configuration files, system binaries, or sensitive data files, potentially leading to privilege escalation, persistent backdoors, or complete system compromise. The vulnerability is particularly concerning in multi-user environments where different users may have varying privilege levels, as it could allow lower-privileged users to manipulate files owned by higher-privileged users. This attack vector can be leveraged in conjunction with other techniques to create more sophisticated exploitation scenarios, such as replacing critical system files or injecting malicious code into running processes. The attack requires local system access but does not need network connectivity, making it particularly stealthy and difficult to detect through traditional network monitoring approaches.
Mitigation strategies for CVE-2014-3423 focus on both immediate patching and operational security improvements. The most effective solution is upgrading to GNU Emacs version 24.4 or later, where the vulnerability has been addressed through improved temporary file handling mechanisms. Organizations should prioritize patching systems running vulnerable versions of GNU Emacs, particularly in environments where local access is possible. Additionally, implementing proper file permissions and using secure temporary file creation methods can help reduce the attack surface. The ATT&CK framework categorizes this vulnerability under T1059 Command and Scripting Interpreter and T1068 Exploitation for Privilege Escalation, as it enables local users to manipulate system resources through legitimate application functionality. System administrators should monitor for unauthorized symbolic link creation in temporary directories and implement file integrity monitoring solutions to detect potential exploitation attempts. Organizations should also consider implementing least privilege principles, ensuring that users running GNU Emacs have minimal necessary permissions and that temporary file directories are properly secured with restrictive permissions to prevent symlink attacks.