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3.7 Low

CVE-2026-12372 A Server-Side Request Forgery (SSRF) vulnerability exists in nltk/nltk versions 3.9.4 and the current develop branch

Description

A Server-Side Request Forgery (SSRF) vulnerability exists in nltk/nltk versions 3.9.4 and the current develop branch. The `nltk.pathsec.validate_network_url()` function, intended to prevent SSRF by rejecting internal network addresses, fails to reject IPs in the RFC 6598 shared address space (`100.64.0.0/10`). This occurs because Python's `ipaddress` module does not classify such addresses as `is_private` or `is_global`, and the current guard only checks `is_private` and a few explicit categories. An attacker who can influence a URL passed to NLTK's network-loading helpers can exploit this vulnerability to make a strict-mode application send requests to shared-address-space hosts, potentially exposing non-public infrastructure reachable from the application host. The impact is limited to SSRF-style confidentiality exposure, with no code execution claimed.

Affected products and versions

Product Affected versions Fixed in
nltk/nltk Versions not published

References

Timeline

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Other CVEs of nltk/nltk

The 12 CVEs of nltk/nltk →
CVE-2026-12261 A vulnerability in `nltk.downloader` in nltk/nltk… 5.3 Medium CVE-2026-12259 In nltk version 3.9.4, the `nltk.downloader.Downloader._download_package()` function writes downloaded package bytes… 5.3 Medium CVE-2026-12252 In nltk/nltk versions 3.9.3 and earlier, five Stanford interface classes (StanfordPOSTagger, StanfordNERTagger,… 7.8 High CVE-2026-12243 NLTK version 3.9.4 is vulnerable to a path traversal attack due to an incomplete fix for GitHub Issue #3504 7.5 High
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