high8.2
CVE-2026-80206
NLTK before 3.10.3 contains a regular expression denial of service (ReDoS) vulnerability in the tgrep module.
Impact
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
| Ecosystem | Package | Affected | Fixed in |
|---|---|---|---|
| pip | nltk | <= 3.10.2 | 3.10.3 |
Affected products
| Vendor | Product | Affected versions |
|---|---|---|
| Nltk | Nltk | before 3.10.3 |
Weakness classification
References
- NVD record
- CVE.org record
- GitHub advisory
- https://github.com/advisories/GHSA-w3v8-gmh9-3wv7
- https://github.com/nltk/nltk/security/advisories/GHSA-w3v8-gmh9-3wv7
- https://nvd.nist.gov/vuln/detail/CVE-2026-80206
- https://github.com/nltk/nltk/commit/0072ea2fb8be22e038a36e887b7061bb6b9339d9
- https://github.com/nltk/nltk/releases/tag/v3.10.3
- https://github.com/pypa/advisory-database/tree/main/vulns/nltk/PYSEC-2026-3751.yaml
- https://www.vulncheck.com/advisories/nltk-3.10.2-regular-expression-denial-of-service-via-tgrep