Bug 2525096 (CVE-2026-81727)

Summary: CVE-2026-81727 nltk: NLTK: Filesystem containment bypass allows local file overwrite
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
Status: NEW --- QA Contact:
Severity: high Docs Contact:
Priority: high    
Version: unspecifiedCC: anpicker, bparees, dschmidt, ebourniv, hasun, jfula, jlanda, jowilson, kshier, nyancey, ometelka, ptisnovs, sbunciak, simaishi, stcannon, syedriko, teagle, xdharmai, yguenane
Target Milestone: ---Keywords: Security
Target Release: ---   
Hardware: All   
OS: Linux   
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A flaw was found in NLTK. This vulnerability, a filesystem containment bypass, allows a local attacker with write access to a shared downloader directory to create special links (hardlinks) that point to files outside the intended installation area. When a package is extracted, these hardlinks can cause files outside the NLTK installation to be overwritten, leading to unauthorized modification or corruption of data.
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oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: --- Target Upstream Version:
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Bug Depends On: 2527833, 2527834    
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Description OSIDB Bzimport 2026-08-27 17:00:08 UTC 
NLTK versions before 3.10.3 contain a filesystem containment bypass vulnerability in the Downloader.download and Downloader.incr_download methods that allows attackers to overwrite files outside the install root through pre-existing hardlinks. Attackers with write access to a shared downloader directory can create hardlinks pointing to outside-root files that are then overwritten during normal package extraction, mutating files outside the intended install tree.