GHSA-vf76-f5cp-9846

Duplicate Advisory: ReDoS in nltk.tgrep via unvalidated user-supplied regular expressions

Published

2026-08-31

Modified

2026-09-02

Sources

github-advisory

Summary

## Duplicate Advisory This advisory has been withdrawn because it is a duplicate of GHSA-w3v8-gmh9-3wv7. This link is maintained to preserve external references. ## Original Description NLTK before 3.10.3 contains a regular expression denial of service (ReDoS) vulnerability in the tgrep module. The _tgrep_node_action function compiles user-supplied regular expressions embedded in /regex/ pattern nodes and executes them via re.search against tree node labels without any validation or timeout. An attacker who controls the tgrep pattern (e.g., via tgrep_positions() or tgrep_compile() exposed to external input) can supply a pattern that triggers catastrophic backtracking, causing indefinite CPU saturation that blocks the Python process.

Affected packages

Remediation: No patched version is listed by GitHub.

References

• https://github.com/advisories/GHSA-vf76-f5cp-9846