CVE-2026-63311
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).
AI Insight
LLM-synthesized narrative grounded in this CVE's description and references.
Affected packages
Versions sourced from the GitHub Security Advisory.
| Package | Affected versions | Patched versions |
|---|---|---|
nltkPyPI | < 3.10.0 | 3.10.0 |
Affected products
2Patches
Vulnerability mechanics
References
8- github.com/nltk/nltk/security/advisories/GHSA-3gqm-fcw5-w839nvdExploitMitigationVendor AdvisoryWEB
- github.com/advisories/GHSA-3gqm-fcw5-w839ghsaADVISORY
- nvd.nist.gov/vuln/detail/CVE-2026-63311ghsaADVISORY
- www.vulncheck.com/advisories/nltk-before-ssrf-via-dns-resolution-failurenvdThird Party AdvisoryWEB
- github.com/nltk/nltk/commit/4a820afa58810cd05049b6c6eae306694d6cfe65ghsaWEB
- github.com/nltk/nltk/pull/3582ghsaWEB
- github.com/nltk/nltk/releases/tag/v3.10.0ghsaWEB
- github.com/pypa/advisory-database/tree/main/vulns/nltk/PYSEC-2026-3723.yamlghsaWEB
News mentions
1- NLTK: Thirteen Path Traversal, RCE, and DoS Vulnerabilities Disclosed TogetherVypr Intelligence · Aug 22, 2026