CVE-2026-79657: NLTK versions before 3.10.3 contain a remote code execution vulnerability in allowlisted pickle loaders that t

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CRITICAL 9.8REMOTEUPGRADE

CVE-2026-79657 is a critical-severity flaw (CVSS 9.8) affecting nltk. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

NLTK versions before 3.10.3 contain a remote code execution vulnerability in allowlisted pickle loaders that trust entire module namespaces instead of specific safe callables. Attackers can craft malicious pickle payloads invoking dangerous in-namespace functions like ReppTokenizer._execute and numpy.f2py.crackfortran.myeval through pickle REDUCE to execute arbitrary commands during model or tokenizer artifact loading.

Why this priority

Critical severity
Public exploit reference
CISA SSVC: automatable with total technical impact
Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	9.8 (Critical)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	1.3% (top 30%)
CISA exploited list	No
Weakness	CWE-502
Published	2026-08-25
Last modified	2026-10-08

Publisher (CNA): VulnCheck · Vendor: nltk

Last updated 2026-10-08 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-08-25 12:16 UTCPublished CVE record published
2026-10-08 16:17 UTCUpdated Record last modified

nltk nltk UPGRADE

Affected: < 3.10.3

Fixed in: 3.10.3

Safe to downgrade to: no unaffected older release

1. Check installed version

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

2. UPGRADE to 3.10.3 (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.

Exact fixes by distribution

Python (pip) · nltk · FIXED · 3.10.3 · vulnerable: <= 3.10.2 · source

pip install --upgrade "nltk>=3.10.3" pip show nltk

Debian 12 · nltk · NO FIX YET

Debian 13 · nltk · NO FIX YET

Public exploits and detection

Public code exists for this CVE. Treat unpatched systems as at risk, and only run PoCs in a lab.

Write-up: github.com/nltk/nltk/security/advisories/GHSA-x99w-6fgc-pmfw

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-2026-79657?

nltk: upgrade to 3.10.3. Exact commands for each OS are on this page.

Is CVE-2026-79657 being exploited?

CVE-2026-79657 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-2026-79657 affect?

CVE-2026-79657 affects nltk. Severity is critical (CVSS 9.8). NLTK versions before 3.10.3 contain a remote code execution vulnerability in allowlisted pickle loaders that trust entire module namespaces instead of specific safe callables. Attackers can craft malicious pickle payloads invoking dangerous

How urgent is CVE-2026-79657?

Priority 65/100. Critical severity; Public exploit reference; CISA SSVC: automatable with total technical impact; Remotely exploitable, no login, no user action

Software pages

Pandas and NumPy vulnerabilities

Related CVEs

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References

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