PYSEC-2026-3741

NLTK versions before 3.10.3 contain a filesystem containment bypass vulnerability in the Downloader.download and Downloader.incrdownload methods that allows attackers to overwrite files outside the install root through pre-existing hardlinks. Attackers with write access to a shared downloader...

PYSEC-2026-3752

NLTK before 3.10.3 contains a regular expression denial of service vulnerability in Pl196xCorpusReader that allows attackers to cause quadratic CPU consumption by supplying malformed TEI blocks with many unmatched opening tags. Attackers can exploit lazy regex patterns in the readblock method...

PYSEC-2026-3739

NLTK before 3.10.3 contains an uncontrolled recursion vulnerability in nltk.featstruct.FeatStructReader that allows unauthenticated attackers to cause a denial of service by supplying deeply nested feature-structure input. Attackers can craft trivial payloads with nested brackets that exceed...

PYSEC-2026-3740

NLTK through 3.10.3 contains a path traversal vulnerability in model-artifact APIs that bypass pathsec enforcement by using raw file operations on caller-controlled paths. Attackers can read or write files outside allowed sandbox roots through TransitionParser, AveragedPerceptron, PerceptronTagge...

CVE-2026-81726

NLTK through 3.10.3 contains a path traversal vulnerability in model-artifact APIs that bypass pathsec enforcement by using raw file operations on caller-controlled paths. Attackers can read or write files outside allowed sandbox roots through TransitionParser, AveragedPerceptron, PerceptronTagge...

CVE-2026-81727

NLTK versions before 3.10.3 contain a filesystem containment bypass vulnerability in the Downloader.download and Downloader.incrdownload methods that allows attackers to overwrite files outside the install root through pre-existing hardlinks. Attackers with write access to a shared downloader...

CVE-2026-81724

NLTK before 3.10.3 contains an uncontrolled recursion vulnerability in nltk.featstruct.FeatStructReader that allows unauthenticated attackers to cause a denial of service by supplying deeply nested feature-structure input. Attackers can craft trivial payloads with nested brackets that exceed...

CVE-2026-81725

NLTK before 3.10.3 contains a regular expression denial of service vulnerability in Pl196xCorpusReader that allows attackers to cause quadratic CPU consumption by supplying malformed TEI blocks with many unmatched opening tags. Attackers can exploit lazy regex patterns in the readblock method...

PYSEC-2026-3741

NLTK versions before 3.10.3 contain a filesystem containment bypass vulnerability in the Downloader.download and Downloader.incrdownload methods that allows attackers to overwrite files outside the install root through pre-existing hardlinks. Attackers with write access to a shared downloader...

Inefficient Algorithmic Complexity

Overview nltk is a Natural Language Toolkit NLTK is a Python package for natural language processing. Affected versions of this package are vulnerable to Inefficient Algorithmic Complexity in the readblock method of TEICorpusView nltk/corpus/reader/pl196x.py, whose lazy .? whole-block regexes...

PYSEC-2026-3738

nltk PorterStemmer in versions = 3.10.2 fixed in 3.10.3 contains an inefficient-algorithmic-complexity denial of service in PorterStemmer.stem. The isconsonant helper walks backward over the entire run of trailing 'y' characters on every call, and measure invokes it for each stem position, causin...

PYSEC-2026-3738

nltk PorterStemmer in versions = 3.10.2 fixed in 3.10.3 contains an inefficient-algorithmic-complexity denial of service in PorterStemmer.stem. The isconsonant helper walks backward over the entire run of trailing 'y' characters on every call, and measure invokes it for each stem position, causin...

CVE-2026-81722

nltk PorterStemmer in versions = 3.10.2 fixed in 3.10.3 contains an inefficient-algorithmic-complexity denial of service in PorterStemmer.stem. The isconsonant helper walks backward over the entire run of trailing 'y' characters on every call, and measure invokes it for each stem position, causin...

CVE-2026-81723

NLTK versions before 3.10.3 contain a quadratic CPU exhaustion vulnerability in XMLCorpusView.readxmlfragment that rescans accumulated XML fragments on every 1 KiB block read. Attackers can provide malformed XML corpus files to cause severe CPU consumption and denial of service through affected...

CVE-2026-81725

NLTK before 3.10.3 contains a regular expression denial of service vulnerability in Pl196xCorpusReader that allows attackers to cause quadratic CPU consumption by supplying malformed TEI blocks with many unmatched opening tags. Attackers can exploit lazy regex patterns in the readblock method...

CVE-2026-81722

nltk PorterStemmer in versions = 3.10.2 fixed in 3.10.3 contains an inefficient-algorithmic-complexity denial of service in PorterStemmer.stem. The isconsonant helper walks backward over the entire run of trailing 'y' characters on every call, and measure invokes it for each stem position, causin...

CVE-2026-81726

NLTK through 3.10.3 contains a path traversal vulnerability in model-artifact APIs that bypass pathsec enforcement by using raw file operations on caller-controlled paths. Attackers can read or write files outside allowed sandbox roots through TransitionParser, AveragedPerceptron, PerceptronTagge...

CVE-2026-81724

NLTK before 3.10.3 contains an uncontrolled recursion vulnerability in nltk.featstruct.FeatStructReader that allows unauthenticated attackers to cause a denial of service by supplying deeply nested feature-structure input. Attackers can craft trivial payloads with nested brackets that exceed...

CVE-2026-81727

NLTK versions before 3.10.3 contain a filesystem containment bypass vulnerability in the Downloader.download and Downloader.incrdownload methods that allows attackers to overwrite files outside the install root through pre-existing hardlinks. Attackers with write access to a shared downloader...

CVE-2026-81723

NLTK versions before 3.10.3 contain a quadratic CPU exhaustion vulnerability in XMLCorpusView.readxmlfragment that rescans accumulated XML fragments on every 1 KiB block read. Attackers can provide malformed XML corpus files to cause severe CPU consumption and denial of service through affected...