{"id":"CVE-2026-78680","aliases":["GHSA-6hwm-xvph-95vm","PYSEC-2026-3868"],"title":"NLTK: Uncontrolled search path when invoking the Graphviz 'dot' binary","summary":"NLTK: Uncontrolled search path when invoking the Graphviz 'dot' binary","severity":"high","cvss":7.8,"cvssVector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H","vendor":"nltk","product":"nltk","ecosystem":"pip","affected":["nltk < 3.10.3"],"patched":["nltk 3.10.3"],"published":"2026-09-01","updated":"2026-09-10","sourceUpdated":"2026-09-10T12:25:25.368160026Z","source":"OSV","sourceUrl":"https://osv.dev/vulnerability/GHSA-6hwm-xvph-95vm","references":[{"url":"https://github.com/nltk/nltk/security/advisories/GHSA-6hwm-xvph-95vm"},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-78680"},{"url":"https://github.com/nltk/nltk/commit/1a3cd1764ab3deb084fb66d0ffb4873717659538"},{"url":"https://github.com/nltk/nltk"},{"url":"https://github.com/nltk/nltk/releases/tag/v3.10.3"},{"url":"https://www.vulncheck.com/advisories/nltk-before-arbitrary-code-execution-via-graphviz-dot-binary"},{"url":"https://pypi.org/project/nltk"},{"url":"https://github.com/advisories/GHSA-6hwm-xvph-95vm"}],"tags":["osv","pip","ghsa"],"epss":0.0012,"epssPercentile":0.0213,"cwe":["CWE-426","CWE-427"],"ingestedAt":"2026-09-01T20:32:02.002Z","slug":"CVE-2026-78680","body":"## Overview\n\nTwo 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).\n\nAffected (<= 3.10.2):\n- `nltk.parse.dependencygraph.dot2img` — called `find_binary(\"dot\")` but discarded the returned validated path and then ran the bare name `[\"dot\", ...]`, so the validation had no effect.\n- `nltk.translate.api.AlignedSent._repr_svg_` — ran the bare name with no validation at all (IPython SVG rendering).\n\nThis is the same class already fixed for the senna, weka, boxer, malt, repp and hunpos wrappers. `nltk.internals.find_binary` 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.\n\n---\n\n## Attack demonstration\nCaptured output, not illustrative. A `./dot` that writes a `PWNED` marker, planted in the CWD with `.` prepended to `PATH`.\n\n**The vulnerable behaviour (old bare-name exec):**\n```\nControl (OLD behavior) — bare ['dot'] in this dir with '.' on PATH:\n  bare ['dot'] executed planted binary = True\n```\n\n**The patched functions refuse it:**\n```\nFIXED code, with ./dot planted and '.' on PATH:\n  dependencygraph.dot2img : Exception \"Cannot find the dot binary...\"  | planted-binary-executed=False  safe\n  AlignedSent._repr_svg_  : Exception \"Cannot find the dot binary...\"  | planted-binary-executed=False  safe\n```\n\n**And `find_binary` itself was attacked directly** (the fix trusts nothing else):\n```\nAttack 1: ./dot in CWD, no dot on PATH            -> LookupError (refused)  safe\nAttack 2: ./dot/dot (dir 'dot' holding 'dot')     -> LookupError (refused)  safe\nAttack 3: '.' on PATH + ./dot                     -> LookupError (refused)  safe\nAttack 4: attacker-writable ABSOLUTE dir on PATH  -> returned /…/evilbin/dot (absolute)\n```\nAttack 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. `find_binary` defends specifically against the CWD/relative injection that bare-name exec is vulnerable to (attacks 1–3), which is exactly what this fix inherits.\n\nEnvironment: python 3.13.7. `dot` is not required to reproduce — the planted binary is the payload.\n\n## Affected packages\n\n- `nltk < 3.10.3`\n\n## Remediation\n\nUpgrade to a patched release:\n\n- `nltk 3.10.3`","depth":"twilight","depthScore":43,"depthScoreParts":{"impact":42.9,"likelihood":0,"exploitation":0,"ransomware":0},"changes":[]}