Vulnerability Details CVE-2026-81727
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.
Exploit prediction scoring system (EPSS) score
EPSS Score 0.001
EPSS Ranking 3.4%
CVSS Severity
CVSS v3 Score 7.1
Products affected by CVE-2026-81727
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cpe:2.3:a:nltk:nltk:2.0.1
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cpe:2.3:a:nltk:nltk:2.0.3
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cpe:2.3:a:nltk:nltk:2.0.4
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cpe:2.3:a:nltk:nltk:3.0.0
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cpe:2.3:a:nltk:nltk:3.0.1
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cpe:2.3:a:nltk:nltk:3.0.2
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cpe:2.3:a:nltk:nltk:3.0.3
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cpe:2.3:a:nltk:nltk:3.0.4
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cpe:2.3:a:nltk:nltk:3.0.5
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cpe:2.3:a:nltk:nltk:3.10.0
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cpe:2.3:a:nltk:nltk:3.10.1
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cpe:2.3:a:nltk:nltk:3.10.2
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cpe:2.3:a:nltk:nltk:3.2.1
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cpe:2.3:a:nltk:nltk:3.2.2
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cpe:2.3:a:nltk:nltk:3.2.3
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cpe:2.3:a:nltk:nltk:3.2.4
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cpe:2.3:a:nltk:nltk:3.2.5
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cpe:2.3:a:nltk:nltk:3.4.1
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cpe:2.3:a:nltk:nltk:3.4.3
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cpe:2.3:a:nltk:nltk:3.4.4
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cpe:2.3:a:nltk:nltk:3.4.5
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cpe:2.3:a:nltk:nltk:3.6.1
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cpe:2.3:a:nltk:nltk:3.6.2
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cpe:2.3:a:nltk:nltk:3.6.3
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cpe:2.3:a:nltk:nltk:3.6.4
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cpe:2.3:a:nltk:nltk:3.6.5
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cpe:2.3:a:nltk:nltk:3.6.6
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cpe:2.3:a:nltk:nltk:3.6.7
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cpe:2.3:a:nltk:nltk:3.8.1
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cpe:2.3:a:nltk:nltk:3.9.1
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cpe:2.3:a:nltk:nltk:3.9.2
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cpe:2.3:a:nltk:nltk:3.9.3
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cpe:2.3:a:nltk:nltk:3.9.4