Junglewise Threat Intelligence

CVE-2026-26007: PyCA cryptography missing subgroup validation in SECT curves

CVE-2026-26007 · Severity: medium · CVSS 6.5 · Published 2026-02-10

Technologies: PyCA Cryptography, Red Hat Enterprise Linux. Vendors: Red Hat, PyPI.

Executive brief

The PyCA cryptography library, a widely used tool for securing Python applications, failed to properly validate certain types of security keys. This flaw could allow an attacker to trick a system into using a weak key, potentially revealing parts of a private encryption key or allowing the forgery of digital signatures. While the issue primarily affects less common 'binary' elliptic curves, it poses a risk to data confidentiality and the integrity of secure communications.

Technical details

The vulnerability exists in the public_key_from_numbers, load_der_public_key, and load_pem_public_key functions of the PyCA cryptography library. These functions fail to verify that a provided public key point belongs to the expected prime-order subgroup of the curve, specifically affecting SECT (binary) curves with a cofactor greater than 1. An attacker can provide a point from a small-order subgroup to perform a subgroup attack. In ECDH key exchange, this can leak the least significant bits of the victim's private key (private_key mod small_subgroup_order). In ECDSA, it allows for the forgery of signatures. The issue is resolved in version 46.0.5 by implementing mandatory subgroup validation for curves with cofactor > 1.

Affected products

  • PyCA cryptography < 46.0.5
  • Red Hat Red Hat Enterprise Linux
  • Red Hat Red Hat OpenShift AI

Timeline

  • 2026-02-10: disclosed
  • 2026-02-10: patched: Fixed in version 46.0.5
  • 2026-02-10: advisory

References

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