cryptography has incomplete DNS name constraint enforcement on peer names
Summary
In versions of cryptography prior to 46.0.5, DNS name constraints were only validated against SANs within child certificates, and not the "peer name" presented during each validation. Consequently, cryptography would allow a peer named bar.example.com to validate against a wildcard leaf certificate for *.example.com, even if the leaf's parent certificate (or upwards) contained an excluded subtree constraint for bar.example.com.
This behavior resulted from a gap between RFC 5280 (which defines Name Constraint semantics) and RFC 9525 (which defines service identity semantics): put together, neither states definitively whether Name Constraints should be applied to peer names. To close this gap, cryptography now conservatively rejects any validation where the peer name would be rejected by a name constraint if it were a SAN instead.
In practice, exploitation of this bypass requires an uncommon X.509 topology, one that the Web PKI avoids because it exhibits these kinds of problems. Consequently, we consider this a medium-to-low impact severity.
See CVE-2025-61727 for a similar bypass in Go's crypto/x509.
Remediation
Users should upgrade to 46.0.6 or newer.
Attribution
Reporter: @1seal
Software afectado
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| Plataforma | Paquete | Versiones vulnerables | Corregida en |
|---|---|---|---|
| Python (PyPI) | cryptography | < 46.0.6 | 46.0.6 |
Referencias
- Vector CVSS
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N- Debilidad (CWE)
CWE-295- Plataforma
- Python (PyPI)
- Paquete
cryptography- Publicada
- 27.03.2026
- Actualizado
- 11.10.2026 15:17
Fuentes y licencias
OSV / GitHub Advisory Database - PYSEC-2026-35 - PyPA Advisory Database; CC BY 4.0
OSV / GitHub Advisory Database - GHSA-m959-cc7f-wv43 - CC BY 4.0
Historial de vulnerabilidades: cryptography
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
- 24
- Primera → última
- 03.2017 08.2026
- Sin corrección
- 0
- Explotada en ataques
- 0
Distribución por gravedad
- Alta 12
- Media 7
- Baja 5
Divulgaciones por año
- 2017: 1
- 2018: 1
- 2019: 0
- 2020: 1
- 2021: 1
- 2022: 1
- 2023: 7
- 2024: 4
- 2025: 1
- 2026: 7
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