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, or a writable/relative entry such as . on PATH) has their binary executed in place of Graphviz (arbitrary code execution).
Affected (<= 3.10.2):
nltk.parse.dependencygraph.dot2img— calledfind_binary("dot")but discarded the returned validated path and then ran the bare name["dot", ...], so the validation had no effect.nltk.translate.api.AlignedSent._repr_svg_— ran the bare name with no validation at all (IPython SVG rendering).
This 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.
Attack demonstration
Captured output, not illustrative. A ./dot that writes a PWNED marker, planted in the CWD with . prepended to PATH.
The vulnerable behaviour (old bare-name exec):
Control (OLD behavior) — bare ['dot'] in this dir with '.' on PATH:
bare ['dot'] executed planted binary = TrueThe patched functions refuse it:
FIXED code, with ./dot planted and '.' on PATH:
dependencygraph.dot2img : Exception "Cannot find the dot binary..." | planted-binary-executed=False safe
AlignedSent._repr_svg_ : Exception "Cannot find the dot binary..." | planted-binary-executed=False safeAnd find_binary itself was attacked directly (the fix trusts nothing else):
Attack 1: ./dot in CWD, no dot on PATH -> LookupError (refused) safe
Attack 2: ./dot/dot (dir 'dot' holding 'dot') -> LookupError (refused) safe
Attack 3: '.' on PATH + ./dot -> LookupError (refused) safe
Attack 4: attacker-writable ABSOLUTE dir on PATH -> returned /…/evilbin/dot (absolute)Attack 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.
Environment: python 3.13.7. dot is not required to reproduce — the planted binary is the payload.
Software afectado
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| Plataforma | Paquete | Versiones vulnerables | Corregida en |
|---|---|---|---|
| Python (PyPI) | nltk | < 3.10.3 | 3.10.3 |
Referencias
- https://github.com/nltk/nltk/security/advisories/GHSA-6hwm-xvph-95vm
- https://nvd.nist.gov/vuln/detail/CVE-2026-78680
- https://github.com/nltk/nltk/commit/1a3cd1764ab3deb084fb66d0ffb4873717659538
- https://github.com/nltk/nltk
- https://github.com/nltk/nltk/releases/tag/v3.10.3
- https://www.vulncheck.com/advisories/nltk-before-arbitrary-code-execution-via-graphviz-dot-binary
- https://pypi.org/project/nltk
- https://github.com/advisories/GHSA-6hwm-xvph-95vm
- Vector CVSS
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H- Debilidad (CWE)
CWE-426, CWE-427- Plataforma
- Python (PyPI)
- Paquete
nltk- Publicada
- 01.09.2026
- Actualizado
- 11.10.2026 15:18
Fuentes y licencias
OSV / GitHub Advisory Database - PYSEC-2026-3868 - PyPA Advisory Database; CC BY 4.0
OSV / GitHub Advisory Database - GHSA-6hwm-xvph-95vm - CC BY 4.0
Historial de vulnerabilidades: nltk
Todas las vulnerabilidades publicadas de este paquete (Python (PyPI)), de la más reciente a la más antigua. Muestra si es un fallo aislado o un paquete que hay que vigilar.
- Entradas en total
- 52
- Primera → última
- 08.2019 09.2026
- Sin corrección
- 6
- Explotada en ataques
- 0
Distribución por gravedad
- Crítica 5
- Alta 32
- Media 13
- Baja 2
Divulgaciones por año
- 2019: 1
- 2020: 0
- 2021: 2
- 2022: 1
- 2023: 0
- 2024: 1
- 2025: 0
- 2026: 47
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