GHSA-qx2g-xrx7-vfh8

Suggest an improvement
Source
https://github.com/advisories/GHSA-qx2g-xrx7-vfh8
Import Source
https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/08/GHSA-qx2g-xrx7-vfh8/GHSA-qx2g-xrx7-vfh8.json
JSON Data
https://api.osv.dev/v1/vulns/GHSA-qx2g-xrx7-vfh8
Aliases
Downstream
CGA (3)
ECHO (1)
Published
2026-08-21T00:31:23Z
Modified
2026-09-10T12:25:44Z
Severity
  • 7.5 (High) CVSS_V3 - CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H CVSS Calculator
  • 8.7 (High) CVSS_V4 - 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 CVSS Calculator
Summary
NLTK TweetTokenizer vulnerable to denial of service through catastrophic regex backtracking
Details

The URLS regular expression in nltk/tokenize/casual.py, compiled into TweetTokenizer.WORD_RE and applied by TweetTokenizer.tokenize, contains a naked-domain branch whose domain-label prefix [a-z0-9]+(?:[.-][a-z0-9]+)* is unbounded. Input consisting of many alternating label separators can be partitioned in exponentially many ways, and because the branch also requires a trailing top-level domain that such input never supplies, the engine explores those partitions before failing at each offset. A few kilobytes of input therefore consumes seconds to minutes of single-threaded CPU, and the HANG_RE substitution performed before matching does not collapse the pattern. TweetTokenizer is intended for tokenizing untrusted social-media text, so any service that applies it, or the module-level casual_tokenize, to submitted text can be stalled per request without authentication. Version 3.10.1 bounds the label repetition.

Database specific 
{
    "cwe_ids":  [
        "CWE-1333"
    ],
    "github_reviewed":  true,
    "github_reviewed_at":  "2026-09-02T15:16:37Z",
    "nvd_published_at":  "2026-08-20T22:18:05Z",
    "severity":  "HIGH"
}
References

Affected packages

PyPI / nltk

Package

Name
nltk
View open source insights on deps.dev
Purl
pkg:pypi/nltk

Affected ranges

Type
ECOSYSTEM
Events
Introduced
0 Unknown introduced version / All previous versions are affected
Fixed
3.10.1

Affected versions

2.*
2.0.1rc2-git
2.0b4
2.0b5
2.0b6
2.0b7
2.0b8
2.0b9
2.0.1rc1
2.0.1rc3
2.0.1rc4
2.0.1
2.0.2
2.0.3
2.0.4
2.0.5
0.*
0.8
0.9
0.9.3
0.9.4
0.9.5
0.9.6
0.9.7
0.9.8
0.9.9
3.*
3.0.0b1
3.0.0b2
3.0.0
3.0.1
3.0.2
3.0.3
3.0.4
3.0.5
3.1
3.2
3.2.1
3.2.2
3.2.3
3.2.4
3.2.5
3.3
3.4
3.4.1
3.4.2
3.4.3
3.4.4
3.4.5
3.5b1
3.5
3.6
3.6.1
3.6.2
3.6.3
3.6.4
3.6.5
3.6.6
3.6.7
3.7
3.8
3.8.1
3.9b1
3.9
3.9.1
3.9.2
3.9.3
3.9.4
3.10.0

Database specific

source 
"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/08/GHSA-qx2g-xrx7-vfh8/GHSA-qx2g-xrx7-vfh8.json"