GHSA-6hwm-xvph-95vm: High severity pip/nltk vulnerability

Two NLTK sites executed the Graphviz dot program by bare name, so process creation resolved it via the search path — and on Windows via the current working directory — rather than a validated absolute location. An attacker who can place a file named dot where resolution looks (the CWD on Windows, or a writable/relative entry such as . on PATH) has their binary executed in place of Graphviz (arbitrary code execution).

Affected (<= 3.10.2): - nltk.parse.dependencygraph.dot2img — called findbinary("dot") but discarded the returned validated path and then ran the bare name ["dot", ...], so the validation had no effect. - nltk.translate.api.AlignedSent.reprsvg — ran the bare name with no validation at all (IPython SVG rendering).

This is the same class already fixed for the senna, weka, boxer, malt, repp and hunpos wrappers. nltk.internals.findbinary refuses a CWD-relative match for a bare tool name and returns only a trusted absolute path; the fix runs that path in both sites.

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Attack demonstration Captured output, not illustrative. A ./dot that writes a PWNED marker, planted in the CWD with . prepended to PATH.

The vulnerable behaviour (old bare-name exec): Control (OLD behavior) — bare ['dot'] in this dir with '.' on PATH: bare ['dot'] executed planted binary = True

The patched functions refuse it: FIXED code, with ./dot planted and '.' on PATH: dependencygraph.dot2img : Exception "Cannot find the dot binary..." | planted-binary-executed=False safe AlignedSent.reprsvg : Exception "Cannot find the dot binary..." | planted-binary-executed=False safe

And findbinary itself was attacked directly (the fix trusts nothing else): Attack 1: ./dot in CWD, no dot on PATH -> LookupError (refused) safe Attack 2: ./dot/dot (dir 'dot' holding 'dot') -> LookupError (refused) safe Attack 3: '.' on PATH + ./dot -> LookupError (refused) safe Attack 4: attacker-writable ABSOLUTE dir on PATH -> returned /…/evilbin/dot (absolute) Attack 4 is out of scope: trusting an absolute directory that is already on PATH is the operating system's own trust model — an attacker who can write to a PATH directory owns the account regardless of NLTK. findbinary defends specifically against the CWD/relative injection that bare-name exec is vulnerable to (attacks 1–3), which is exactly what this fix inherits.

Environment: python 3.13.7. dot is not required to reproduce — the planted binary is the payload.