CVE-2026-78680: NLTK Uncontrolled Search Path When Invoking Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-6hwm-xvph-95vm",
  "modified" : "2026-09-01T20:27:20Z",
  "published" : "2026-09-01T20:27:20Z",
  "aliases" : [ "CVE-2026-78680" ],
  "summary" : "NLTK: Uncontrolled search path when invoking the 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.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H"
  }, {
    "type" : "CVSS_V4",
    "score" : "CVSS:4.0/AV:L/AC:L/AT:N/PR:L/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "PyPI",
      "name" : "nltk"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "3.10.3"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 3.10.2"
    }
  } ],
  "references" : [ {
    "type" : "WEB",
    "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" : "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"
  }, {
    "type" : "WEB",
    "url" : "https://www.vulncheck.com/advisories/nltk-before-arbitrary-code-execution-via-graphviz-dot-binary"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-426", "CWE-427" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-09-01T20:27:20Z",
    "nvd_published_at" : null
  }
}