CVE-2026-80206
NLTK before 3.10.3 contains a regular expression denial of service (ReDoS) vulnerability in the tgrep module.
Does this matter?
High impact if exploited, but EPSS currently rates exploitation as unlikely (0.26%). Schedule it in the normal patch cycle and watch for a rise in EPSS or a public exploit.
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.
- CVSS 4.0
- 8.2 HIGHCVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/M
- EPSS
- 0.26% probability · 18th percentile
- CISA KEV
- Not listed
- Weakness
- CWE-1333
- Affected
- nltk/nltk
- Source
- disclosure@vulncheck.com
References
- https://github.com/nltk/nltk/security/advisories/GHSA-w3v8-gmh9-3wv7Exploit, Vendor Advisory
- https://www.vulncheck.com/advisories/nltk-3.10.2-regular-expression-denial-of-service-via-tgrepThird Party Advisory
- https://github.com/nltk/nltk/security/advisories/GHSA-w3v8-gmh9-3wv7Exploit, Vendor Advisory
Source: NVD record, EPSS from FIRST.org, KEV from CISA. Refreshed daily.