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Fencer Intel
high 7.5

CVE-2026-81722 json

nltk PorterStemmer before 3.10.3 Quadratic-time DoS

published 2mo ago modified 2mo ago also EUVD-2026-67072 , GHSA-ww6m-cw3f-q94g , PYSEC-2026-3738

cvss
7.5
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.5%
EPSS 0.5% chance of exploitation in 30 days, percentile 44%
public exploits
0
none known

Summary

nltk PorterStemmer in versions <= 3.10.2 (fixed in 3.10.3) contains an inefficient-algorithmic-complexity denial of service in PorterStemmer.stem(). The _is_consonant() helper walks backward over the entire run of trailing 'y' characters on every call, and _measure() invokes it for each stem position, causing O(n^2) behavior. A single ~20-50 KB untrusted token consisting of a long run of the letter 'y' followed by a matching suffix (e.g., 'ness') can pin a CPU core for seconds to minutes, causing availability impact.

Patch / fix

  • pypi nltk 3.10.3
  • nltk nltk 3.10.3
  • nltk Debian 14 3.10.3-1

debian advisories DEBIAN-CVE-2026-81722

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Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2026-81722 updated cvss 7.5

nltk: nltk PorterStemmer: Denial of Service due to inefficient token processing

  • Red Hat Exploit Intelligence exploit-intelligence-tech-preview/vulnerability-analysis-rhel9
    affected: workaround, no fix planned “Will not fix”
  • Red Hat Lightspeed Core lightspeed-core/rag-tool-cpu-rhel9, lightspeed-core/lightspeed-stack-rhel9, lightspeed-core/rag-tool-cuda-12.9-rhel9 Red Hat OpenShift Lightspeed openshift-lightspeed/lightspeed-service-api-rhel9
    affected: workaround, no fix available
  • Red Hat Ansible Automation Platform 2 ansible-automation-platform-25/lightspeed-chatbot-rhel8
    affected: workaround, no fix planned “Will not fix”
  • Red Hat OpenShift AI (RHOAI) rhoai/odh-ogx-core-rhel9
    affected: workaround, no fix available
  • Red Hat OpenShift AI 2.25 rhoai/odh-ta-lmes-job-rhel9 1791553527, rhoai/odh-llama-stack-core-rhel9 1791873747, rhoai/odh-pipeline-runtime-pytorch-llmcompressor-cuda-py312-rhel9 1791867208, rhoai/odh-workbench-jupyter-pytorch-llmcompressor-cuda-py312-rhel9 1791867189
    fixed: vendor fix RHSA-2026:87410
  • Red Hat OpenShift AI 3.3 rhoai/odh-llama-stack-core-rhel9 1789121286
    fixed: vendor fix RHSA-2026:73987
  • Red Hat OpenShift AI 3.4 rhoai/odh-ta-lmes-job-rhel9 1791470318, rhoai/odh-llama-stack-core-rhel9 1790958470, rhoai/odh-trustyai-garak-lls-provider-dsp-rhel9 1791785804, rhoai/odh-trustyai-nemo-guardrails-server-rhel9 1791556128
    fixed: vendor fix RHSA-2026:84734
  • Red Hat OpenShift AI 3.5 rhoai/odh-ta-lmes-job-rhel9 1788935863, rhoai/odh-trustyai-garak-lls-provider-dsp-rhel9 1791953275, rhoai/odh-trustyai-nemo-guardrails-server-rhel9 1791566631
    fixed: vendor fix RHSA-2026:69539
show 2 more
  • Red Hat OpenShift Lightspeed openshift-lightspeed/lightspeed-ocp-rag-rhel9, openshift-lightspeed-tech-preview/lightspeed-rag-tool-rhel9
    not affected: vulnerable code not in execute path
  • Red Hat OpenShift AI 2.25 rhoai/odh-rhel9-operator 1792570619, rhoai/odh-vllm-cpu-rhel9 1792018436, rhoai/odh-dashboard-rhel9 1791853525, rhoai/odh-modelmesh-rhel9 1790881700, rhoai/odh-operator-bundle 1792571069, rhoai/odh-vllm-cuda-rhel9 1791358976, +62 more Red Hat OpenShift AI 3.3 rhoai/odh-cli-rhel9 1790070206, rhoai/rhai-cli-rhel9 1790070206, rhoai/odh-mlflow-rhel9 1789653606, rhoai/odh-trainer-rhel9 1790136369, rhoai/odh-maas-api-rhel9 1790131842, rhoai/odh-mlserver-rhel9 1789121365, +76 more Red Hat OpenShift AI 3.4 rhoai/odh-cli-rhel9 1791509689, rhoai/rhai-cli-rhel9 1791509689, rhoai/odh-automl-rhel9 1791535789, rhoai/odh-mlflow-rhel9 1791865967, rhoai/odh-autorag-rhel9 1791557539, rhoai/odh-trainer-rhel9 1791869783, +96 more Red Hat OpenShift AI 3.5 rhoai/odh-cli-rhel9 1789525149, rhoai/odh-cli-rhel9 1791945905, rhoai/rhai-cli-rhel9 1789525149, rhoai/rhai-cli-rhel9 1791945905, rhoai/odh-automl-rhel9 1789363166, rhoai/odh-automl-rhel9 1791916705, +229 more
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
Proof of concept is public
Automatable
yes
Technical impact
partial
Assessed
2mo ago

Exploit prediction

0.52% chance of exploitation in the next 30 days, higher than 44% of all scored CVEs (FIRST EPSS, 2026-11-11).

Exploits and checks

  • github.com https://github.com/nltk/nltk/security/advisories/GHSA-ww6m-cw3f-q94g referenced PoC, tagged "exploit" by a source, unverified

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
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
<3.10.3
3.10.3

Affected products

  • nltk nltk

Classification

Weakness
  • CWE-407 Inefficient Algorithmic Complexity

References

Sources

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.