Vulnerability · Published Aug 22, 2026 · Assigned by VulnCheck

CVE-2026-70626NLTK before 3.9.4 Symlink Escape via CorpusReader

Medium 6.2

In plain English

A medium-severity security flaw in nltk from nltk. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 0.2% (higher than 10% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 3.1)6.2Medium

Exploit odds (30 days)0.2%top 90.1% of all CVEs

Exploited in the wildNo reportsCISA SSVC: poc

Attack toolingNoneno public tooling known

Official description

NLTK versions before 3.9.4 contain a symlink escape vulnerability in CorpusReader.open() that allows local attackers to read arbitrary files outside the corpus root. The vulnerability exists because path validation is lexical and does not account for symlink resolution, enabling attackers to place symlinks inside the corpus root to access files outside the intended boundary.

Affected packages & fixed versions

Ecosystem	Package	Fixed in	Advisory
Debian:12	nltk	no fix listed	DEBIAN-CVE-2026-70626
Debian:13	nltk	no fix listed	DEBIAN-CVE-2026-70626
Debian:14	nltk	3.10.0-1	DEBIAN-CVE-2026-70626
PyPI	nltk	3.9.4	GHSA-r6gq-whwq-mvg9
PyPI	nltk	3.9.4	PYSEC-2026-3732
Ubuntu:26.10	nltk	no fix listed	UBUNTU-CVE-2026-70626

Affected products (as reported)

Vendor	Product	Versions
nltk	nltk	0 – before 3.9.4

Weakness: CWE-59 · Vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N

References

GitHub Security Advisory (GHSA-r6gq-whwq-mvg9) vendor-advisory
VulnCheck Advisory: NLTK before 3.9.4 Symlink Escape via CorpusReader third-party-advisory