Vulnerability Description
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 rebinding can bypass SSRF protections and reach restricted network resources, including cloud metadata endpoints (e.g., 169.254.169.254).
CVSS Score
MEDIUM
Related Weaknesses (CWE)
References
- https://github.com/nltk/nltk/security/advisories/GHSA-3gqm-fcw5-w839
- https://www.vulncheck.com/advisories/nltk-before-ssrf-via-dns-resolution-failure
FAQ
What is CVE-2026-63311?
CVE-2026-63311 is a vulnerability with a CVSS score of 5.3 (MEDIUM). 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 ca...
How severe is CVE-2026-63311?
CVE-2026-63311 has been rated MEDIUM with a CVSS base score of 5.3/10. Review the CVSS metrics above for detailed severity breakdown.
Is there a patch for CVE-2026-63311?
Check the references section above for vendor advisories and patch information. Review vendor security bulletins for remediation guidance.