Staging Environment: Content and features may be unstable or change without notice.
Advisory details: github_osv / GHSA-vf76-f5cp-9846
Advisory ID github_osv/GHSA-vf76-f5cp-9846
Aliases
Summary Duplicate Advisory: ReDoS in nltk.tgrep via unvalidated user-supplied regular expressions ## Duplicate Advisory This advisory has been withdrawn because it is a duplicate of GHSA-w3v8-gmh9-3wv7. This link is maintained to preserve external references. ## Original 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.
Status Published
Exploitability 0.5
Weighted Severity 7.4
Risk 3.7
Affected and Fixed Packages Package Details
Introduced and Fixed Package Commit Patches Package Commit Patches Details
Weaknesses (1)
CWE-1333 Inefficient Regular Expression Complexity
System Score Found at
cvssv3.1 5.9 https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/08/GHSA-vf76-f5cp-9846/GHSA-vf76-f5cp-9846.json
cvssv4 8.2 https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/08/GHSA-vf76-f5cp-9846/GHSA-vf76-f5cp-9846.json
generic_textual HIGH
Reference id Reference type URL
CVE-2026-80206 https://nvd.nist.gov/vuln/detail/CVE-2026-80206
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://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/08/GHSA-vf76-f5cp-9846/GHSA-vf76-f5cp-9846.json
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
Vector: 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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X Found at https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/08/GHSA-vf76-f5cp-9846/GHSA-vf76-f5cp-9846.json
Attack Vector (AV) Attack Complexity (AC) Attack Requirements (AT) Privileges Required (PR) User Interaction (UI) Vulnerable System Impact Confidentiality (VC) Vulnerable System Impact Integrity (VI) Vulnerable System Impact Availability (VA) Subsequent System Impact Confidentiality (SC) Subsequent System Impact Integrity (SI) Subsequent System Impact Availability (SA)

network

adjacent

local

physical

low

high

none

present

none

low

high

none

passive

active

high

low

none

high

low

none

high

low

none

high

low

none

high

low

none

high

low

none

There are no SSVC decisions available.