CVE-2014-3424 in Emacs
Summary
by MITRE
lisp/net/tramp-sh.el in GNU Emacs 24.3 and earlier allows local users to overwrite arbitrary files via a symlink attack on a /tmp/tramp.##### temporary file.
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Analysis
by VulDB Data Team • 06/20/2021
The vulnerability identified as CVE-2014-3424 resides within the tramp-sh.el component of GNU Emacs version 24.3 and earlier, representing a significant security flaw that enables local attackers to perform unauthorized file overwrites through symbolic link manipulation. This issue specifically targets the temporary file handling mechanism used by the TRAMP (Transparent Remote Access Method) package when establishing remote connections through shell protocols. The vulnerability manifests when Emacs creates temporary files in the /tmp directory during remote file operations, failing to properly validate the existence and ownership of these temporary files before writing to them.
The technical implementation of this vulnerability stems from insufficient validation of temporary file creation processes within the TRAMP subsystem. When Emacs establishes a remote connection using shell-based protocols, it generates temporary files in the /tmp directory with predictable naming patterns such as tramp.#### where #### represents a sequence number. The flaw occurs because the application does not verify that the temporary file is actually a regular file and not a symbolic link pointing to another location on the filesystem. An attacker can create a symbolic link with the same name in the /tmp directory before Emacs creates its temporary file, causing Emacs to write data to the target file specified by the symbolic link instead of the intended temporary file.
This vulnerability directly maps to CWE-377: Insecure Temporary File and CWE-59: Improper Link Resolution, both of which are classified under the broader category of insecure file handling practices in software development. The operational impact of this vulnerability is substantial as it allows local users to overwrite arbitrary files on the system with the privileges of the user running Emacs. Attackers can leverage this to overwrite configuration files, system binaries, or sensitive data files, potentially leading to privilege escalation or system compromise. The attack vector is particularly concerning because it requires minimal privileges and can be executed without network access, making it a persistent threat within local environments.
The attack scenario involves an attacker creating a symbolic link in the /tmp directory that points to a target file they wish to overwrite, then triggering a remote file operation in Emacs that would create the temporary file. This technique can be combined with other local privilege escalation methods or used to plant malicious content in system files. From an attacker's perspective, this vulnerability aligns with ATT&CK technique T1059.006 for executing commands through shell-based protocols and T1078 for gaining access through valid accounts. The vulnerability affects all versions of GNU Emacs prior to 24.4, and users should immediately upgrade to patched versions to mitigate the risk. Organizations should also implement monitoring for suspicious file creation patterns in the /tmp directory and consider restricting the use of TRAMP functionality in environments where local privilege escalation risks are significant. The fix for this vulnerability involved implementing proper file validation checks that ensure temporary files are created with appropriate permissions and that symbolic links are not followed during temporary file creation processes, thereby preventing the symlink attack vector from succeeding.