CVE-2026-2641: Universal-ctags DoS Vulnerability

CVE-2026-2641 Overview

A vulnerability has been identified in universal-ctags ctags up to version 6.2.1. The affected element is the parseExpression/parseExprList function within the file parsers/v.c of the V Language Parser component. This weakness allows an attacker to trigger uncontrolled recursion through manipulation of crafted input, leading to a denial of service condition. The vulnerability requires local access to exploit and a proof-of-concept has been made publicly available.

Critical Impact

Local attackers can cause denial of service through uncontrolled recursion in the V Language Parser, potentially crashing the ctags process when processing maliciously crafted V language files.

Affected Products

• Universal Ctags up to version 6.2.1
• V Language Parser component (parsers/v.c)
• Systems using ctags for code indexing and navigation

Discovery Timeline

• 2026-02-18 - CVE-2026-2641 published to NVD
• 2026-02-18 - Last updated in NVD database

Technical Details for CVE-2026-2641

Vulnerability Analysis

This vulnerability is classified under CWE-404 (Improper Resource Shutdown or Release) and manifests as an uncontrolled recursion issue within the V Language Parser of universal-ctags. When processing specially crafted V language source files, the parseExpression and parseExprList functions in parsers/v.c fail to properly limit recursion depth, allowing deep or infinite recursive calls that exhaust the call stack.

The vulnerability has a local attack vector, requiring an attacker to either place a malicious V language file in a location where ctags will process it, or convince a user to run ctags against a malicious file. While the impact is limited to availability (denial of service), this could affect development workflows that rely on ctags for code navigation and indexing.

Root Cause

The root cause lies in insufficient recursion depth checks within the expression parsing routines of the V Language Parser. The parseExpression and parseExprList functions recursively parse nested expressions without implementing proper depth limiting or tail-call optimization, making them susceptible to stack exhaustion attacks when processing deeply nested or malformed expression structures in V language source files.

Attack Vector

The attack requires local access to the target system. An attacker would craft a V language source file (.v extension) containing deeply nested or specially structured expressions designed to trigger excessive recursion in the parsing functions. When a user or automated system runs ctags against this malicious file, the parser enters an uncontrolled recursive loop, eventually exhausting stack space and causing the process to crash.

The attack could be delivered through:

• Placing malicious .v files in project directories where automated code indexing occurs
• Submitting malicious files to code repositories where ctags runs as part of the build or indexing pipeline
• Social engineering users to process the malicious file

A proof-of-concept demonstrating this vulnerability is available at the GitHub PoC Repository. The vulnerability was reported to the ctags project via GitHub Issue #4369, but no response has been received as of the publication date.

Detection Methods for CVE-2026-2641

Indicators of Compromise

• Unexpected ctags process crashes or terminations when processing V language files
• High CPU utilization by ctags processes followed by sudden termination
• Segmentation fault errors in system logs related to ctags execution
• Presence of unusually structured or deeply nested .v files in project directories

Detection Strategies

• Monitor for ctags process crashes and segmentation faults in system logs
• Implement file integrity monitoring on code repositories to detect suspicious .v file additions
• Use resource monitoring to detect processes consuming excessive stack memory before crashing
• Review recently added or modified V language files for unusual nesting patterns

Monitoring Recommendations

• Configure process monitoring to alert on repeated ctags failures
• Set up log aggregation to correlate ctags crashes with file processing events
• Implement automated scanning of incoming code submissions for potentially malicious constructs
• Monitor system resource utilization patterns for anomalous stack consumption

How to Mitigate CVE-2026-2641

Immediate Actions Required

• Restrict ctags processing of V language files from untrusted sources
• Implement resource limits (e.g., ulimit stack size) when running ctags
• Review and validate V language files before processing in automated pipelines
• Consider temporarily disabling V language parsing if not required

Patch Information

As of the last update on 2026-02-18, no official patch has been released by the universal-ctags project. The vulnerability was reported via GitHub Issue #4369, but the project has not yet responded. Users should monitor the universal-ctags GitHub repository for updates and apply patches as soon as they become available.

Workarounds

• Apply resource limits to ctags processes to contain potential denial of service impact
• Exclude V language files from ctags processing using --languages=-V flag when V parsing is not needed
• Implement file validation or sandboxing for ctags processing of untrusted input
• Use container isolation when running ctags on potentially untrusted codebases

# Configuration example: Limit stack size and exclude V language parsing
ulimit -s 8192  # Limit stack size to 8MB
ctags --languages=-V --recurse /path/to/project