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CVE-2026-12252 nltk CVE debrief

CVE-2026-12252 is a high-severity vulnerability (CVSS Score: 7.8) affecting nltk/nltk versions 3.9.3 and earlier. The vulnerability exists in five Stanford interface classes: StanfordPOSTagger, StanfordNERTagger, StanfordParser, StanfordDependencyParser, and StanfordNeuralDependencyParser. These classes accept user-controllable JAR paths and execute them via the `java()` function, which invokes `subprocess.Popen()` without integrity verification. This allows for arbitrary code execution when loading untrusted JAR files. The vulnerability is identical to CVE-2026-0848, which was previously fixed for StanfordSegmenter by adding SHA256 verification. However, this fix was not applied to the affected classes, leaving them vulnerable.

Vendor
nltk
Product
nltk/nltk
CVSS
HIGH 7.8
CISA KEV
Not listed in stored evidence
Original CVE published
2026-07-04
Original CVE updated
2026-07-08
Advisory published
2026-07-04
Advisory updated
2026-07-08

Who should care

Developers and users of the nltk/nltk library, particularly those using versions 3.9.3 and earlier, should be aware of this vulnerability. The vulnerability's high severity and potential for arbitrary code execution make it a priority for defenders to address.

Technical summary

The vulnerability exists in the nltk/nltk library, specifically in the five Stanford interface classes: StanfordPOSTagger, StanfordNERTagger, StanfordParser, StanfordDependencyParser, and StanfordNeuralDependencyParser. These classes execute user-controllable JAR paths via the `java()` function, which invokes `subprocess.Popen()` without integrity verification. This allows for arbitrary code execution when loading untrusted JAR files. The vulnerability is a result of not applying the SHA256 verification fix, previously applied to StanfordSegmenter, to these classes.

Defensive priority

High priority should be given to defenders to address this vulnerability, as it allows for arbitrary code execution. Defenders should prioritize updating to a patched version of nltk/nltk or implementing compensating controls to mitigate the risk.

Recommended defensive actions

  • Update nltk/nltk to a patched version, if available.
  • Implement SHA256 verification for JAR files loaded by the affected classes.
  • Restrict access to the affected classes and JAR files.
  • Monitor for suspicious activity related to JAR file loading.
  • Consider implementing additional security controls, such as sandboxing or isolation, for the affected classes and JAR files.

Evidence notes

The vulnerability was reported by [email protected] and is documented in the CVE-2026-12252 record on CVE.org and the NVD detail page. The vulnerability's existence and details are corroborated by multiple sources, including the nltk/nltk library and the Huntr bug bounty platform.

Sources and references

Verified primary and authoritative sources

  • CVE-2026-12252 CVE Program record

    Publisher, destination, and source semantics verified

    URL: https://www.cve.org/CVERecord?id=CVE-2026-12252

    CVE Program - Official CVE Program record with source-provided CVE metadata.

  • CVE-2026-12252 NVD vulnerability detail

    Publisher, destination, and source semantics verified

    URL: https://nvd.nist.gov/vuln/detail/CVE-2026-12252

    NIST National Vulnerability Database - Official NIST NVD detail page and source-specific vulnerability assessment.

Supplemental 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.