Staging Environment: Content and features may be unstable or change without notice.
Advisory details: github_osv / GHSA-pf76-q698-37v8
Advisory ID github_osv/GHSA-pf76-q698-37v8
Aliases
Summary Duplicate Advisory: Uncontrolled recursion in nltk.featstruct.FeatStructReader causes unhandled RecursionError (DoS) via deeply nested feature-structure input ## Duplicate Advisory This advisory has been withdrawn because it is a duplicate of GHSA-cw6x-m8jw-qmrh. This link is maintained to preserve external references. ## Original Description NLTK before 3.10.3 contains an uncontrolled recursion vulnerability in nltk.featstruct.FeatStructReader that allows unauthenticated attackers to cause a denial of service by supplying deeply nested feature-structure input. Attackers can craft trivial payloads with nested brackets that exceed Python's recursion limit and raise an unhandled RecursionError, crashing applications that parse user-supplied feature structures or feature grammars.
Status Published
Exploitability 0.5
Weighted Severity 6.2
Risk 3.1
Affected and Fixed Packages Package Details
Introduced and Fixed Package Commit Patches Package Commit Patches Details
Weaknesses (1)
CWE-674 Uncontrolled Recursion
System Score Found at
cvssv3.1 5.3 https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/08/GHSA-pf76-q698-37v8/GHSA-pf76-q698-37v8.json
cvssv4 6.9 https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/08/GHSA-pf76-q698-37v8/GHSA-pf76-q698-37v8.json
generic_textual MODERATE
Reference id Reference type URL
https://github.com/nltk/nltk/security/advisories/GHSA-cw6x-m8jw-qmrh
https://www.vulncheck.com/advisories/nltk-before-3.10.3-denial-of-service-via-uncontrolled-recursion
CVE-2026-81724 https://nvd.nist.gov/vuln/detail/CVE-2026-81724
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:L/PR:N/UI:N/S:U/C:N/I:N/A:L Found at https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/08/GHSA-pf76-q698-37v8/GHSA-pf76-q698-37v8.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:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/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-pf76-q698-37v8/GHSA-pf76-q698-37v8.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.