NLTK versions before 3.10.3 fail to use validated absolute paths when invoking the Graphviz dot binary in dependencygraph.dot2img and AlignedSent.repr_svg, allowing attackers to execute arbitrary code by placing a malicious dot binary in the search path or current working directory. Attackers can exploit bare-name binary resolution on Windows via the current working directory or on Unix-like systems via relative PATH entries to execute their binary instead of the legitimate Graphviz tool.