CVE catalog
CVE-2026-81725
NLTK before 3.10.3 contains a regular expression denial of service vulnerability in Pl196xCorpusReader that allows attackers to cause quadratic CPU consumption by supplying malformed TEI blocks with m
- Severity
- Medium · CVSS 6.3
CVSS:4.0/AV:N/AC:H/AT:P/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 - Published
- Updated
- Source
- [NVD] · [CVE record]
- EPSS
- 0.37% · Oct 25, 2026
NLTK before 3.10.3 contains a regular expression denial of service vulnerability in Pl196xCorpusReader that allows attackers to cause quadratic CPU consumption by supplying malformed TEI blocks with many unmatched opening tags. Attackers can exploit lazy regex patterns in the read_block method through public APIs like words() and tagged_words() to force repeated rescans and achieve near-quadratic runtime growth.
Vulnerable and fixed packages
Distribution-reported package versions and fixes. These do not depend on matching against the OpenFactory package catalog.
| Distribution | Package | Release | Version | Status |
|---|---|---|---|---|
| Debian | nltk | sid | 3.10.3-1 | fixed |
| Debian | nltk | forky | 3.10.3-1 | fixed |
| Debian | nltk | trixie | 3.9.1-2 | vulnerable |
| Debian | nltk | bookworm | 3.8-1 | vulnerable |
| Cpe | nltk | Not reported | 3.10.3 | fixed |
| PyPI | nltk | Not reported | 3.10.3 | fixed |
| Pip | nltk | Not reported | 3.10.3 | fixed |
| Ubuntu | nltk | pro | 3.9.1-2 | vulnerable |
| Ubuntu | nltk | pro | 3.9.1-2build1 | vulnerable |
| Ubuntu | nltk | pro | 3.9.2-1 | vulnerable |
| Ubuntu | nltk | pro | 3.9.2-1ubuntu0.1~esm1 | vulnerable |
| Ubuntu | nltk | pro | 3.9.2-1ubuntu0.1~esm2 | vulnerable |
Fixed-version evidence
| Distribution | Package | Type | Release | Fixed version | Urgency | Origin | Bugs |
|---|---|---|---|---|---|---|---|
| Debian | nltk | source | sid | 3.10.3-1 | not yet assigned | Not reported | Not reported |
| Debian | nltk | source | forky | 3.10.3-1 | not yet assigned | Not reported | Not reported |
| Debian | nltk | source | trixie | (unfixed) | not yet assigned | Not reported | Not reported |
| Debian | nltk | source | bookworm | (unfixed) | not yet assigned | Not reported | Not reported |
| Cpe | nltk | cpe | Not reported | 3.10.3 | Not reported | NVD-CVE-2026-81725 | Not reported |
| PyPI | nltk | PyPI | Not reported | 3.10.3 | Not reported | PYSEC-2026-3752 | Not reported |
| Pip | nltk | pip | Not reported | 3.10.3 | Not reported | GHSA-8MPW-7FPC-4GQJ | Not reported |
Notes
[trixie] nltk: Minor issue [bookworm] nltk: Minor issue
OpenFactory catalog packages
[Debian 12 (Bookworm)]
- [python3-nltk]Affected
Source package: [nltk]
Details (2)
3.8-1· all · bookwormAffected
nvd · nltk · debian · bookworm; nvd · nltk · debian · 12
3.8-1· all · bookwormAffected
nvd · nltk · debian · bookworm; nvd · nltk · debian · 12
[Debian 13 (Trixie)]
- [python3-nltk]Affected
Source package: [nltk]
Details (2)
3.9.1-2· all · trixieAffected
nvd · nltk · debian · 13
3.9.1-2· all · trixieAffected
nvd · nltk · debian · 13
Observed:
References
- [https://github.com/advisories/GHSA-8mpw-7fpc-4gqj]
- [https://nvd.nist.gov/vuln/detail/CVE-2026-81725]
- [https://osv.dev/vulnerability/DEBIAN-CVE-2026-81725]
- [https://osv.dev/vulnerability/UBUNTU-CVE-2026-81725]
- [https://security-tracker.debian.org/tracker/CVE-2026-81725]
- [https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-81725.json]
[Debian Security Tracker] · [FIRST EPSS] · [GitHub Advisory Database] · [National Vulnerability Database (NVD)] · [OSV Package Vulnerability Database] · [Red Hat security advisories and VEX]