CVE-2026-71514 nltk CVE debrief

Who should care

Organizations and developers using NLTK 3.9.4 through 3.10.2 should be aware of this vulnerability and take steps to mitigate it. They should verify their inventory, review compensating controls, and apply patches or updates to ensure version 3.10.3 or later is used. Security teams should monitor for suspicious activity and implement additional security measures to prevent potential attacks.

Technical summary

The CrubadanCorpusReader in NLTK 3.9.4 through 3.10.2 contains a path traversal vulnerability. The _load_lang_ngrams function joins the corpus root with crubadan_code, read from the corpus table.txt mapping file, and opens the result using the built-in open() function instead of a pathsec-validated opener. This allows attackers to disclose file contents outside the corpus root through lang_freq, limited to paths ending in -3grams.txt. Affected organizations should verify their NLTK version and apply patches or mitigations.

Defensive priority

Organizations using NLTK 3.9.4 through 3.10.2 should verify their inventory and apply patches or mitigations to prevent potential path traversal attacks.

Recommended defensive actions

• Verify NLTK version and apply patches or updates to ensure version 3.10.3 or later is used.
• Restrict access to sensitive files and directories to prevent unauthorized disclosure.
• Implement compensating controls, such as monitoring and exception tracking, to detect potential attacks.
• Consider setting ENFORCE to enable nltk.pathsec containment checks.
• Review corpus package controls and lang_freq usage.
• Monitor for suspicious file accesses and implement additional security measures.
• Track exceptions and retest remediated assets.

Evidence notes

The CVE-2026-71514 vulnerability in NLTK's CrubadanCorpusReader allows attackers to disclose file contents outside the corpus root through lang_freq, limited to paths ending in -3grams.txt. The issue arises from the use of os.path.join, which discards the root when the column-0 value from the corpus table.txt mapping file is absolute. To verify, defenders should review corpus package controls, check for lang_freq usage, and monitor for suspicious file accesses.

Sources and references

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.