NLTK before 3.10.0 (affected versions <= 3.9.4) contains a server-side request forgery (SSRF) vulnerability in the validate_network_url() function in nltk/pathsec.py. The _resolve_hostname() helper c
NLTK before 3.10.0 (affected versions <= 3.9.4) contains a server-side request forgery (SSRF) vulnerability in the validate_network_url() function in nltk/pathsec.py. The _resolve_hostname() helper catches OSError and ValueError during socket.getaddrinfo() and returns an empty list; when DNS resolution fails, the validation loop executes no IP checks and the function fails open, allowing urlopen() to proceed without validation. An attacker who can trigger DNS resolution failures or use DNS rebi
Affected packages
- nltk
Exploit signal
- Known exploited (CISA KEV)
- No
- EPSS score
- —
- EPSS percentile
- —
EPSS is the probability a CVE is exploited in the wild; percentile is its rank among all CVEs.
Sources
- https://www.cve.org/CVERecord?id=CVE-2026-63311
- https://github.com/nltk/nltk/security/advisories/ghsa-3gqm-fcw5-w839
- https://security-tracker.debian.org/tracker/cve-2026-63311
- https://github.com/cveproject/cvelistv5/tree/main/cves/2026/63xxx/cve-2026-63311.json
- https://nvd.nist.gov/vuln/detail/cve-2026-63311
- https://www.vulncheck.com/advisories/nltk-before-ssrf-via-dns-resolution-failure
Structured record: https://ubuntu.com/security/CVE-2026-63311
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