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.

Attack Vector Network

Attack Complexity Low

Privileges Required None

Attack Requirements None

User Interaction None

Vulnerable System Confidentiality Impact None

Vulnerable System Integrity Impact None

Vulnerable System Availability Impact High

Subsequent System Confidentiality Impact None

Subsequent System Integrity Impact None

Subsequent System Availability Impact None

Attack Vector Network

Attack Complexity Low

Privileges Required None

Scope Unchanged

Confidentiality Impact None

Integrity Impact None

Availability Impact High

User Interaction None

No CVSS v3.0

No CVSS v2

This CVE is not in the KEV list.

No EPSS score available.

Key SSVC decision points have not yet been added.

Default status is the baseline for the product, each version can override it (e.g. patched versions marked unaffected).

Vendor Product Default status Versions
nltk nltk unaffected
Version Status Constraints
0 affected < 3.10.3
3.10.3 unaffected —

No data.

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Project Subscriptions

Vendors Products
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Advisories

No advisories yet.

Fixes

Solution

No solution given by the vendor.

Workaround

No workaround given by the vendor.

References
Link Providers
https://github.com/nltk/nltk/security/advisories/GHSA-ww6m-cw3f-q94g cve-icon cve-icon
https://www.vulncheck.com/advisories/nltk-porterstemmer-before-3.10.3-quadratic-time-dos cve-icon cve-icon
History

Thu, 27 Aug 2026 16:45:00 +0000

Type Values Removed Values Added
Description 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.
Title nltk PorterStemmer before 3.10.3 Quadratic-time DoS
First Time appeared Nltk
Nltk nltk
Weaknesses CWE-407
CPEs cpe:2.3:a:nltk:nltk:*:*:*:*:*:*:*:*
Vendors & Products Nltk
Nltk nltk
References
Metrics cvssV3_1

{'score': 7.5, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H'}

cvssV4_0

{'score': 8.7, 'vector': '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'}

Projects

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cve-icon MITRE

Status: PUBLISHED

Assigner: VulnCheck

Published:

Updated: 2026-08-27T14:51:15.857Z

Reserved: 2026-08-27T11:13:14.064Z

Link: CVE-2026-81722

cve-icon Vulnrichment

No data.

cve-icon NVD

Status : Received

Published: 2026-08-27T17:21:02.800

Modified: 2026-08-27T17:21:02.800

Link: CVE-2026-81722

cve-icon Redhat

No data.

cve-icon OpenCVE Enrichment

No data.

Weaknesses