VDB
CVE-2026-81722
CVE-2026-81722
PUBLISHED
CVSS 8.7 HIGH
Reported by VulnCheck · Published August 27, 2026
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.
Risk Scores
CVSS 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
Affected Products
| Vendor | Product | Versions |
|---|---|---|
| nltk | nltk | 0, 3.10.3 |
| chainguard | nemo | 0 |
| PyPI | nltk | 0 |
| wolfi | open-webui | 0 |
| nltk | nltk | 0, 3.10.3 |
| chainguard | open-webui | 0 |
Timeline
- Aug 27, 2026 Coalition ESS Score
- Aug 27, 2026 CVE Published
- Aug 28, 2026 EPSS Score
- Aug 30, 2026 EPSS Score
- Sep 1, 2026 EPSS Score
- Sep 2, 2026 Security Advisory
- Sep 6, 2026 EPSS Score
- Sep 9, 2026 EPSS Score
- Sep 12, 2026 EPSS Score
- Sep 16, 2026 EPSS Score
- Sep 18, 2026 EPSS Score
- Sep 24, 2026 EPSS Score
References
- GitHub Security Advisory (GHSA-ww6m-cw3f-q94g) vendor-advisory
- VulnCheck Advisory: nltk PorterStemmer before 3.10.3 Quadratic-time DoS third-party-advisory
- https://nvd.nist.gov/vuln/detail/CVE-2026-81722 advisory
- https://github.com/advisories/GHSA-ww6m-cw3f-q94g advisory
- https://github.com/nltk/nltk/commit/7808692d451b962711005d954859bb83aabcf8fa patch
- https://github.com/nltk/nltk/releases/tag/v3.10.3 url
- https://github.com/pypa/advisory-database/tree/main/vulns/nltk/PYSEC-2026-3738.yaml advisory