CVE-2026-126298 json
NLTK before 3.10.4 Quadratic CPU Denial of Service via Tree.chomsky_normal_form
published 20d ago modified yesterday also EUVD-2026-125223 , GHSA-r53h-rw34-8h97
- cvss
- 7.5
- version 3.1, CNA
- cisa kev
- Not listed
- not in CISA's catalog
- epss
- 0.6%
- EPSS 0.6% chance of exploitation in 30 days, percentile 48%
- public exploits
- 0
- none known
Summary
NLTK before 3.10.4 contains a denial of service vulnerability in Tree.chomsky_normal_form that allows remote attackers to exhaust CPU through quadratic-time right-factor binarization using list.pop(0). Attackers can supply a wide flat treebank tree parsed by Tree.fromstring to force tens of seconds of single-threaded CPU consumption, blocking the processing thread.
Patch / fix
- pypi nltk 3.10.4
- nltk nltk 3.10.4
- github.com/nltk/nltk@457ebe3 commit
- github.com/nltk/nltk@677857d commit
- github.com/nltk/nltk#3909 pull request
- github.com/nltk/nltk/releases/tag/v3.10.4 release
Is CVE-2026-126298 in your dependencies? Fencer shows which of your repositories are affected as soon as an advisory lands, and opens the fix as a pull request.
Check with FencerCISA SSVC
- Exploitation
- none
- Automatable
- yes
- Technical impact
- partial
- Assessed
- yesterday
Exploit prediction
0.58% chance of exploitation in the next 30 days, higher than 48% of all scored CVEs (FIRST EPSS, 2026-11-14).
CVSS scores
| assigned by | version | score | vector |
|---|---|---|---|
| CNA | 4.0 | 8.7 | 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 |
| CNA | 3.1 | 7.5 | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H |
| GitHub | 3.1 | 7.5 | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H |
| CNA | 4.0 | 8.7 | 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 |
Affected packages
| ecosystem | package | affected | fixed in |
|---|---|---|---|
| pypi | nltk | <3.10.4 |
3.10.4 |
Affected products
- nltk nltk
Classification
References
-
github.com
/nltk/nltk/pull/3909
web
-
github.com
/nltk/nltk/commit/457ebe349f8dd8080224f76a64aff806dd437057
web
-
github.com
/nltk/nltk/commit/677857dcafd84e4591865d976b562a27dfde566e
web
-
github.com
/nltk/nltk/security/advisories/GHSA-r53h-rw34-8h97
vendor-advisory, web, advisory
-
vulncheck.com
/advisories/nltk-before-3.10.4-quadratic-cpu-denial-of-service-via-tree-chomsky-normal-form
third-party-advisory, web
-
nvd.nist.gov
/vuln/detail/CVE-2026-126298
advisory
-
github.com
/nltk/nltk
package
-
github.com
/nltk/nltk/releases/tag/v3.10.4
web
Sources
- CVE List CVE-2026-126298
- GitHub Advisory GHSA-r53h-rw34-8h97
- NVD CVE-2026-126298
- Maintainer advisory GHSA-r53h-rw34-8h97
Fencer Intel keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.
The maintainers of nltk/nltk published their own advisory on GitHub. Reviewed sources take precedence over it.