Staging Environment: Content and features may be unstable or change without notice.
Advisory details: gitlab / pypi/nltk/CVE-2026-80206
Advisory ID gitlab/pypi/nltk/CVE-2026-80206
Aliases CVE-2026-80206
GHSA-w3v8-gmh9-3wv7
Summary NLTK: ReDoS in nltk.tgrep via unvalidated user-supplied regular expressions The NLTK `tgrep` module accepts user-supplied regular expressions and passes them to the Python `re` engine without a timeout or validation, enabling catastrophic backtracking (ReDoS). Applications that expose the `tgrep` API to external input are vulnerable to a single-request denial of service that blocks the Python process indefinitely.
Status Published
Exploitability 0.5
Weighted Severity 0.0
Risk
Affected and Fixed Packages Package Details
Introduced and Fixed Package Commit Patches Package Commit Patches Details
Weaknesses (3)
CWE-1333 Inefficient Regular Expression Complexity
CWE-937 OWASP Top Ten 2013 Category A9 - Using Components with Known Vulnerabilities
CWE-1035 OWASP Top Ten 2017 Category A9 - Using Components with Known Vulnerabilities
System Score Found at
cvssv3.1 https://gitlab.com/gitlab-org/advisories-community/-/blob/main/pypi/nltk/CVE-2026-80206.yml
Reference id Reference type URL
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
CVE-2026-80206 https://nvd.nist.gov/vuln/detail/CVE-2026-80206
GHSA-w3v8-gmh9-3wv7 https://github.com/advisories/GHSA-w3v8-gmh9-3wv7
GHSA-w3v8-gmh9-3wv7 Advisory https://github.com/nltk/nltk/security/advisories/GHSA-w3v8-gmh9-3wv7
nltk-3.10.2-regular-expression-denial-of-service-via-tgrep Advisory https://www.vulncheck.com/advisories/nltk-3.10.2-regular-expression-denial-of-service-via-tgrep
No exploits are available.

No EPSS data available for this advisory.

Patch URL
There are no known patches.
Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H Found at https://gitlab.com/gitlab-org/advisories-community/-/blob/main/pypi/nltk/CVE-2026-80206.yml
Attack Vector (AV) Attack Complexity (AC) Privileges Required (PR) User Interaction (UI) Scope (S) Confidentiality Impact (C) Integrity Impact (I) Availability Impact (A)

network

adjacent_network

local

physical

low

high

none

low

high

none

required

unchanged

changed

high

low

none

high

low

none

high

low

none

There are no SSVC decisions available.