PYSEC-2026-3868 NLTK: Uncontrolled search path when invoking the Graphviz 'dot' binary

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, ...