Medium severity5.9NVD Advisory· Published Aug 26, 2026· Updated Sep 1, 2026
CVE-2026-80206
CVE-2026-80206
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.
AI Insight
LLM-synthesized narrative grounded in this CVE's description and references.
Affected packages
Versions sourced from the GitHub Security Advisory.
| Package | Affected versions | Patched versions |
|---|---|---|
nltkPyPI | < 3.10.3 | 3.10.3 |
Affected products
1Patches
Vulnerability mechanics
References
7- github.com/nltk/nltk/security/advisories/GHSA-w3v8-gmh9-3wv7nvdExploitVendor AdvisoryWEB
- github.com/advisories/GHSA-w3v8-gmh9-3wv7ghsaADVISORY
- nvd.nist.gov/vuln/detail/CVE-2026-80206ghsaADVISORY
- www.vulncheck.com/advisories/nltk-3.10.2-regular-expression-denial-of-service-via-tgrepnvdThird Party AdvisoryWEB
- github.com/nltk/nltk/commit/0072ea2fb8be22e038a36e887b7061bb6b9339d9ghsaWEB
- github.com/nltk/nltk/releases/tag/v3.10.3ghsaWEB
- github.com/pypa/advisory-database/tree/main/vulns/nltk/PYSEC-2026-3751.yamlghsaWEB
News mentions
1- Nltk Library: 16 Vulnerabilities Including Critical RCE Disclosed in BatchVypr Intelligence · Aug 27, 2026