CVE-2026-80206
NLTK 3.10.2 Regular Expression Denial of Service via tgrep
- State
- Published
- Severity
- 8.2 High
- Published
- Aug 26, 2026
- Updated
- Aug 26, 2026
- Reserved
- Aug 25, 2026
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.
Scores
| CVSS | Score | Vector | Source |
|---|---|---|---|
| 4.0 | 8.2 High | CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N | VulnCheck |
| 3.1 | 5.9 Medium | CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H | VulnCheck |
Weaknesses
- CWE-1333 Inefficient Regular Expression Complexity
Affected Products
| Product | Versions |
|---|---|
nltknltk |
|
References
- GitHub Security Advisory (GHSA-w3v8-gmh9-3wv7)vendor-advisory
- VulnCheck Advisory: NLTK 3.10.2 Regular Expression Denial of Service via tgrepthird-party-advisory
Every record here comes from the CVE Program’s CVE List. © 1999–2026 The MITRE Corporation. CVE is a registered trademark of The MITRE Corporation. The records are reproduced under the CVE Program terms of use.