Machine-written summary
Summary written by Claude Haiku from the source advisory. Not reviewed by a person.
The nltk package before 3.10.0 is vulnerable to a denial of service through the Text.findall() and TokenSearcher.findall() methods, which pass user-supplied regular expressions to the regex engine without timeout or validation, allowing catastrophic backtracking. An unauthenticated attacker who can reach an application exposing these methods with external input can send a single request that saturates CPU indefinitely, blocking other users of the Python process. Upgrade to nltk 3.10.0 or later.
Not analysed yet
We haven’t published our analysis of this Advisory yet. Once a person has reviewed it, this page will say what’s vulnerable, what has to be true for your app to be affected, and how to check.
Severity and exploitation
| Score | Rating | CVSS | Vector | Source |
|---|---|---|---|---|
| 8.7 | High | 4.0 | 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 (VulnCheck) |
- CISA KEV Not listed.
- EPSS 0.0065, the 51st percentile, on 14 Nov 2026: FIRST’s estimate of the chance of exploitation in the next 30 days.
Timeline
- 31 Oct 2026, 14:38 UTC First seen by agentprime
- 31 Oct 2026, 14:38 UTC Confirmed by OSV
Sources
- GitHub Advisory Database: GHSA-rrv8-h7p8-rx55
- OSV: GHSA-rrv8-h7p8-rx55
- github.com/nltk/nltk/security/advisories/GHSA-rrv8-h7p8-rx55
- nvd.nist.gov/vuln/detail/CVE-2026-80205
- github.com/nltk/nltk/pull/3674
- github.com/nltk/nltk/commit/d8e47539317b571ab1422981f5b9653d5eae1249
- github.com/nltk/nltk
- github.com/nltk/nltk/releases/tag/v3.10.0
- github.com/pypa/advisory-database/tree/main/vulns/nltk/PYSEC-2026-3750.yaml
- www.vulncheck.com/advisories/nltk-before-3.10.0-redos-via-text-findall-unvalidated-regex
- www.openwall.com/lists/oss-security/2026/09/01/3