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TI-2026-56373 Aliases CVE-2026-81725GHSA-8mpw-7fpc-4gqj

NLTK before 3.10.3 Regular Expression Denial of Service via Pl196xCorpusReader

Priority LOW 28CWE-400Published · Updated

Key facts

Attack vector
Network
Privileges required
None
User interaction
None
Attack complexity
High
Attack requirements
Present
Impact type
Denial of service
Confidentiality · integrity · availability
None · None · Low
Fix status
Partial Red Hat: 2 fixed, 5 without a fix

Attack profile from CVSS 4.0 · CNA. Fix status from CNA, GitHub and Red Hat. Impact type from CWE-400.

Summary

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.

Why it matters now

Exploitation None reported CISA SSVC · not in CISA KEV
EPSS 0.00369 30th percentileScored 2026-11-07
Public exploit Yes 1 exploit referenceTagged by NVD
Fix Partial nltk (nltk): 3.10.3nltk (PyPI): 3.10.3Red Hat: 2 advisoriesRed Hat: 2 fixed, 5 without a fix

SSVC decision points

CISA ADP · SSVC 2.0.3

Exploitation
None
Automatable
No
Technical impact
Partial

The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.

Affected products

VendorProductAffected versionsFixed inStatusSource
nltknltkbefore 3.10.33.10.3Patch availableCNA
—nltk (PyPI)before 3.10.33.10.3Patch availableGHSA-8mpw-7fpc-4gqj
  • nltk Vendornltk Affected before 3.10.3 Fixed in 3.10.3 Patch available CNA
  • nltk (PyPI) Vendor— Affected before 3.10.3 Fixed in 3.10.3 Patch available GHSA-8mpw-7fpc-4gqj

CPE configurations NVD · 1

CPEVersionsRoleVendor
cpe:2.3:a:nltk:nltk:*:*:*:*:*:*:*:*before 3.10.3Vulnerablenltk
  • cpe:2.3:a:nltk:nltk:*:*:*:*:*:*:*:* Versions before 3.10.3 Vulnerable ·nltk

Remediation

  • Fix · CNA nltk (nltk) Fixed in 3.10.3
  • Fix · GHSA-8mpw-7fpc-4gqj nltk (PyPI) Fixed in 3.10.3 Advisory →

Red Hat 2 advisories

  • RHSA-2026:86891 Released 2026-10-21 · Red Hat rating Critical
    RHOAI 3.5.2 - Red Hat OpenShift AI
    • Red Hat OpenShift AI 3.5 registry.redhat.io/rhoai/odh-automl-rhel9, registry.redhat.io/rhoai/odh-built-in-detector-rhel9, registry.redhat.io/rhoai/odh-cli-rhel9 +47
  • RHSA-2026:84734 Released 2026-10-19 · Red Hat rating Critical
    RHOAI 3.4.5 - Red Hat OpenShift AI
    • Red Hat OpenShift AI 3.4 registry.redhat.io/rhoai/odh-ai-gateway-payload-processing-rhel9, registry.redhat.io/rhoai/odh-automl-rhel9, registry.redhat.io/rhoai/odh-autorag-rhel9 +47

Fixed in the same release

Records fixed by the same vendor advisory or release, as the CNA lists them.

  • Release ·

    nltk 3.10.3

    5 records Highest priority Priority HIGH 2 HIGH, 2 MEDIUM, 1 LOW

    Other records, highest priority first

    • TI-2026-56370 nltk PorterStemmer before 3.10.3 Quadratic-time DoSPriority HIGH 77
    • TI-2026-56372 NLTK before 3.10.3 Denial of Service via Uncontrolled RecursionPriority HIGH 70
    • TI-2026-56375 NLTK before 3.10.3 Hardlink File Overwrite via downloaderPriority MEDIUM 64
    Show all 5 records →

Vendor assessments

Red Hat

Red Hat rating: Moderate. Red Hat's page for this CVE →

ProductStatusPlan or fix
Exploit IntelligenceAffectedNo fix planned: Will not fix
Lightspeed CoreAffectedNo fix planned: Will not fix
OpenShift LightspeedAffectedNo fix planned: Will not fix
Red Hat Ansible Automation Platform 2AffectedNo fix planned: Will not fix
Red Hat OpenShift AI (RHOAI)AffectedNo fix planned: Will not fix
Red Hat OpenShift AI 3.4Fixed RHSA-2026:84734
Red Hat OpenShift AI 3.5Fixed RHSA-2026:86891
Not affected: 3 products
  • OpenShift Lightspeed
  • Red Hat OpenShift AI 3.4
  • Red Hat OpenShift AI 3.5

Timeline

  1. 2026-10-02 Threatist record created from CVE-2026-81725
  2. 2026-10-03 Alias added: GHSA-8mpw-7fpc-4gqj
  3. 2026-10-07 Affected versions changed · Red Hat
  4. 2026-10-20 Fix available: RHSA-2026:84734 · Red Hat
  5. 2026-10-20 Fix available: Red Hat OpenShift AI 3.4 · Red Hat
  6. 2026-10-22 Fix available: RHSA-2026:86891 · Red Hat
  7. 2026-10-22 Fix available: Red Hat OpenShift AI 3.5 · Red Hat

References

Exploit 1

Advisory 1

Other 4

  • TI-2026-00629 Arbitrary Code Execution in NLTK StanfordSegmenter via Untrusted JAR Loading CVSS 3.0CRITICAL 10.0
  • TI-2025-12800 Zip Slip Vulnerability in nltk/nltk Leading to Remote Code Execution CVSS 3.0CRITICAL 10.0
  • TI-2026-55173 NLTK before 3.10.3 JVM Argument Injection via Per-Call Options CVSS 4.0CRITICAL 9.3
  • TI-2026-55155 NLTK before 3.10.3 Remote Code Execution via Unsafe Pickle Deserialization CVSS 4.0CRITICAL 9.3
  • TI-2026-56370 nltk PorterStemmer before 3.10.3 Quadratic-time DoS CVSS 4.0HIGH 8.7
  • TI-2026-55172 NLTK 3.10.2 Path Traversal via corpus-reader constructors CVSS 4.0HIGH 8.8
See all 41 →

Sources

This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences