NLTK before 3.10.0 (affected versions <= 3.9.4) contains a server-side request forgery (SSRF) vulnerability in the validate_network_url() function… (CVE-2026-63311)
NLTK versions up to 3.9.4 contain a server-side request forgery (SSRF) vulnerability in the validate_network_url() function. The vulnerability arises because DNS resolution failures cause the function to skip IP checks, allowing unvalidated URLs to be accessed. This can enable attackers to bypass SSRF protections and access restricted network resources such as cloud metadata endpoints. The issue is fixed starting from version 3.10.0.
AI Analysis
Technical Summary
NLTK before version 3.10.0 (specifically versions <= 3.9.4) has an SSRF vulnerability in the validate_network_url() function located in nltk/pathsec.py. The helper function _resolve_hostname() catches OSError and ValueError exceptions during DNS resolution via socket.getaddrinfo() and returns an empty list. When DNS resolution fails, the validation loop does not perform IP address checks, causing the function to fail open. This allows the urlopen() call to proceed without proper validation. Attackers who can cause DNS resolution failures or use DNS rebinding techniques can exploit this to reach restricted internal network resources, including sensitive cloud metadata endpoints such as 169.254.169.254.
Potential Impact
An attacker can bypass SSRF protections in affected NLTK versions and potentially access internal or restricted network resources that should be protected. This could lead to information disclosure or unauthorized access to sensitive endpoints like cloud metadata services. The CVSS score of 5.3 reflects a moderate severity with no direct confidentiality impact but with integrity impact due to the potential for unauthorized requests.
Mitigation Recommendations
Upgrade NLTK to version 3.10.0 or later, where this SSRF vulnerability is fixed. Patch status is confirmed by the versioning information indicating that versions <= 3.9.4 are affected and 3.10.0 is the fixed version. No vendor advisory content was provided, so check the official NLTK release notes or security advisories for confirmation and further guidance.
NLTK before 3.10.0 (affected versions <= 3.9.4) contains a server-side request forgery (SSRF) vulnerability in the validate_network_url() function… (CVE-2026-63311)
Description
NLTK versions up to 3.9.4 contain a server-side request forgery (SSRF) vulnerability in the validate_network_url() function. The vulnerability arises because DNS resolution failures cause the function to skip IP checks, allowing unvalidated URLs to be accessed. This can enable attackers to bypass SSRF protections and access restricted network resources such as cloud metadata endpoints. The issue is fixed starting from version 3.10.0.
CVSS v3.1
Score 5.3medium
Affected software
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Weaknesses
AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
NLTK before version 3.10.0 (specifically versions <= 3.9.4) has an SSRF vulnerability in the validate_network_url() function located in nltk/pathsec.py. The helper function _resolve_hostname() catches OSError and ValueError exceptions during DNS resolution via socket.getaddrinfo() and returns an empty list. When DNS resolution fails, the validation loop does not perform IP address checks, causing the function to fail open. This allows the urlopen() call to proceed without proper validation. Attackers who can cause DNS resolution failures or use DNS rebinding techniques can exploit this to reach restricted internal network resources, including sensitive cloud metadata endpoints such as 169.254.169.254.
Potential Impact
An attacker can bypass SSRF protections in affected NLTK versions and potentially access internal or restricted network resources that should be protected. This could lead to information disclosure or unauthorized access to sensitive endpoints like cloud metadata services. The CVSS score of 5.3 reflects a moderate severity with no direct confidentiality impact but with integrity impact due to the potential for unauthorized requests.
Mitigation Recommendations
Upgrade NLTK to version 3.10.0 or later, where this SSRF vulnerability is fixed. Patch status is confirmed by the versioning information indicating that versions <= 3.9.4 are affected and 3.10.0 is the fixed version. No vendor advisory content was provided, so check the official NLTK release notes or security advisories for confirmation and further guidance.
Technical Details
- Gcve Source
- db.gcve.eu
- Osv Id
- GHSA-qg9p-xrhj-435m
- Osv Schema Version
- 1.4.0
- Aliases
- ["CVE-2026-63311"]
- Ecosystems
- []
- Database Specific Severity
- MODERATE
- Cvss Version
- 3.1
Threat ID: 6a8a27f7acd9273b499bc98a
Added to database: 08/22/2026, 22:51:35 UTC
Last enriched: 08/22/2026, 22:53:16 UTC
Last updated: 08/23/2026, 01:44:03 UTC
Views: 6
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