CPU exhaustion via quadratic trailing-y scans
Published Aug 27, 2026 · Updated Aug 27, 2026
Algorithmic-complexity denial of service in NLTK 3.10.2 and earlier allows attackers to interrupt processing with a crafted token. _measure() calls _is_consonant() at each position, and that helper repeatedly scans backward across each trailing-y run, producing quadratic work. Reachability requires a consuming application to pass an untrusted 20–50 KB token ending in a triggering suffix such as ness; one token pins one process's CPU core for seconds to minutes.
Summary
What happened
Algorithmic-complexity denial of service in NLTK 3.10.2 and earlier allows attackers to interrupt processing with a crafted token. _measure() calls _is_consonant() at each position, and that helper repeatedly scans backward across each trailing-y run, producing quadratic work. Reachability requires a consuming application to pass an untrusted 20–50 KB token ending in a triggering suffix such as ness; one token pins one process's CPU core for seconds to minutes.
The record
- CVE
- CVE-2026-81722
- Published
- Aug 27, 2026
- Updated
- Aug 27, 2026
- Vendor
- NLTK Project
- Product
- NLTK
- Classifications
- CWE-407, T1499.004
- Attack vector
- Unavailable
- Privileges
- Unavailable
Timeline
How it unfolded
- Aug 27, 2026CVE publishedPublication date reported by the CVE source.
- Aug 27, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
Compare these published version ranges with your installed build and any vendor patches.
- Affected versionversion=0 <3.10.3
What conditions does exploitation require?
What is affected?
Published CVSS scores
No CVSS assessment is available in this record.
CVSS describes severity. EPSS estimates exploitation probability.
Attacks
What attackers are doing with it
Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.
Weakness, pattern, technique
Public exploit references
- GHSA-ww6m-cw3f-q94g PorterStemmer proof of conceptproof of concept · demonstrated
Labels summarize the accepted research assessment. They do not indicate a test against your environment.
Technologies
Your stack
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Your stack
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