Staging Environment: Content and features may be unstable or change without notice.
Advisory details: github_osv / GHSA-cv2g-m8rr-888c
Advisory ID github_osv/GHSA-cv2g-m8rr-888c
Aliases
Summary Duplicate Advisory: Natural Language Toolkit (NLTK) has unbounded recursion in JSONTaggedDecoder.decode_obj() may cause DoS ## Duplicate Advisory This advisory has been withdrawn because it is a duplicate of GHSA-rf74-v2fm-23pw. This link is maintained to preserve external references. ## Original Description NLTK versions before 3.9.4 contain an unbounded recursion vulnerability in JSONTaggedDecoder.decode_obj() that allows attackers to cause denial of service by supplying deeply nested JSON structures. Attackers can craft JSON payloads exceeding the recursion limit to trigger an unhandled RecursionError that crashes the Python process.
Status Published
Exploitability 0.5
Weighted Severity 7.8
Risk 3.9
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 7.5 https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/08/GHSA-cv2g-m8rr-888c/GHSA-cv2g-m8rr-888c.json
cvssv4 8.7 https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/08/GHSA-cv2g-m8rr-888c/GHSA-cv2g-m8rr-888c.json
generic_textual HIGH
Reference id Reference type URL
https://github.com/nltk/nltk
https://github.com/nltk/nltk/security/advisories/GHSA-rf74-v2fm-23pw
https://www.vulncheck.com/advisories/nltk-before-denial-of-service-via-jsontaggeddecoder
CVE-2026-66393 https://nvd.nist.gov/vuln/detail/CVE-2026-66393
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:H Found at https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/08/GHSA-cv2g-m8rr-888c/GHSA-cv2g-m8rr-888c.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: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-cv2g-m8rr-888c/GHSA-cv2g-m8rr-888c.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.