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Vulnerabilities

Vulnerability · CVE-2026-63311

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.

Published Aug 22, 2026 · catalog updated Oct 14, 2026 · NLTK before 3.10.0 (affected

Check if you run it

No confirmed exploitation is on record for CVE-2026-63311. EPSS is 0.33%. Act only if a listed version of NLTK before 3.10.0 (affected is installed.

Gaps on this record

  • The stored product name is a package slug. The name on this page is taken from the title (NLTK before 3.10.0 (affected).
  • No vendor fix or required action is stored. Compare the linked advisory before you change production.
Severity
Medium6.9
Known exploitation
Not in CISA/VulnCheck KEV
EPSS
0.33%
Remediation
Version ranges on file
Affected products
cpe nltk/nltk · stated nltk

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).

Are you affected?

Enter the version you run. The result uses only the ranges stored on this record.

The check returns affected, not affected, or incomplete. It does not guess a version that is missing from the record.

  • cpe nltk/nltkversion unspecified
  • stated nltk<= 3.9.4

How to fix CVE-2026-63311

What to do

Three questions, each answered from this record only. Confirm the vendor advisory before you patch.

Should you patch?

No confirmed exploitation is on record for CVE-2026-63311. EPSS is 0.33%. Act only if a listed version of NLTK before 3.10.0 (affected is installed.

Which versions are affected?

Compare what you have installed with <= 3.9.4. Compare the installed version with the linked vendor advisory before you change production.

What should an analyst verify?

CWE-918: Server-Side Request Forgery (SSRF). EPSS 0.33%. There is no CISA KEV listing. No Exploit-DB or Metasploit reference is linked. Use the source links for the original advisory.

Code

The project this record applies to. Exploit listings stay in References.

No public source repository is identified for this product.

Timeline

Detection, updates, and resolution for this record.

  1. Aug 22, 2026 · NIST NVD

    Detected

    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()

  2. Oct 14, 2026 · NIST NVD

    Updated

    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()

Sources

  • CVE.orgVulnerability recordCVE-2026-63311

    Official CVE identifier

    cve.org
  • FIRST EPSSExploitation probabilityCVE-2026-63311

    30-day exploitation probability 0.3%

    first.org
  • NIST NVDVulnerability recordCVE-2026-63311

    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 li

    nvd.nist.gov

References

Freshness

Last verified in this catalog Oct 18, 2026. Significant claims (KEV, EPSS, CVSS, affected ranges) come from the source rows above — open the original publisher for the authoritative advisory.