CVE-2026-63311: NLTK before 3.10.0 (affected versions <= 3.9.4) contains a server-side request forgery (SSRF) vulnerability in

Q: How do I fix CVE-2026-63311?

nltk: upgrade to 3.10.0. Exact commands for each OS are on this page.

Q: Is CVE-2026-63311 being exploited?

CVE-2026-63311 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

Q: What does CVE-2026-63311 affect?

CVE-2026-63311 affects nltk. Severity is medium (CVSS 5.3). 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 sock

Q: How urgent is CVE-2026-63311?

Priority 35/100. Public exploit reference; Remotely exploitable, no login, no user action

This week

MEDIUM 5.3REMOTEUPGRADE

CVE-2026-63311 is a medium-severity flaw (CVSS 5.3) affecting nltk. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

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 ca

Why this priority

Public exploit reference
Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	5.3 (Medium)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	0.3% (top 73%)
CISA exploited list	No
Weakness	CWE-918
Published	2026-08-22
Last modified	2026-10-14

Publisher (CNA): VulnCheck · Vendor: nltk

Last updated 2026-10-14 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-08-22 15:16 UTCPublished CVE record published
2026-10-14 13:10 UTCUpdated Record last modified

nltk nltk UPGRADE

Affected: < 3.10.0

Fixed in: 3.10.0

Safe to downgrade to: no unaffected older release

1. Check installed version

apt-cache policy nltk || rpm -q nltk || nltk --version

2. UPGRADE to 3.10.0 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade nltk

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade nltk

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2026-63311?

nltk: upgrade to 3.10.0. Exact commands for each OS are on this page.

Is CVE-2026-63311 being exploited?

CVE-2026-63311 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2026-63311 affect?

CVE-2026-63311 affects nltk. Severity is medium (CVSS 5.3). 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 sock

How urgent is CVE-2026-63311?

Priority 35/100. Public exploit reference; Remotely exploitable, no login, no user action

Related CVEs

CVE-2026-12252 HIGH 7.8 UPGRADE In nltk/nltk versions 3.9.3 and earlier, five Stanford interface classes (StanfordPOSTagger, StanfordNERTagger
CVE-2026-12259 MEDIUM 6.5 DOWNGRADE In nltk version 3.9.4, the `nltk.downloader.Downloader._download_package()` function writes downloaded package
CVE-2026-12261 MEDIUM 6.5 UPGRADE A vulnerability in `nltk.downloader` in nltk/nltk versions <= 3.9.4 allows for cross-package resource and mode
CVE-2026-12372 LOW 3.7 DOWNGRADE A Server-Side Request Forgery (SSRF) vulnerability exists in nltk/nltk versions 3.9.4 and the current develop
CVE-2026-71513 HIGH 8.8 UPGRADE NLTK before 3.10.3 contains a remote code execution vulnerability in AllowlistUnpickler that validates only th

References

← Back to latest CVEs