{"id":"CVE-2026-78680","aliases":["GHSA-6hwm-xvph-95vm","PYSEC-2026-3868"],"url":"https://o3.security/vulnerability/CVE-2026-78680","summary":"NLTK before 3.10.3 Arbitrary Code Execution via Graphviz dot Binary","details":"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).\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.","published":"2026-08-25T01:30:37.044Z","modified":"2026-09-25T03:48:42.050216763Z","cvss":null,"epss":{"score":0.0012,"percentile":0.02077,"asOf":"2026-09-07"},"cisaKev":null,"exploitsKnown":0,"affectedPackages":[{"ecosystem":"PyPI","name":"nltk","fixedVersion":"3.10.3"}],"fix":{"url":"https://github.com/nltk/nltk/commit/1a3cd1764ab3deb084fb66d0ffb4873717659538","label":"nltk/nltk@1a3cd17"},"references":[{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/78xxx/CVE-2026-78680.json"},{"type":"ADVISORY","url":"https://github.com/nltk/nltk/security/advisories/GHSA-6hwm-xvph-95vm"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-78680"},{"type":"ADVISORY","url":"https://www.vulncheck.com/advisories/nltk-before-arbitrary-code-execution-via-graphviz-dot-binary"},{"type":"WEB","url":"https://github.com/nltk/nltk/commit/1a3cd1764ab3deb084fb66d0ffb4873717659538"},{"type":"PACKAGE","url":"https://github.com/nltk/nltk"},{"type":"WEB","url":"https://github.com/nltk/nltk/releases/tag/v3.10.3"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-09-25T03:48:42.050216763Z"}}