Insufficient verification of data authenticity in cryptography - CVE-2026-26007

Detailed vulnerability description

The vulnerability allows a remote attacker to gain access to potentially sensitive information.

The vulnerability exists due to the public_key_from_numbers (or EllipticCurvePublicNumbers.public_key()), EllipticCurvePublicNumbers.public_key(), load_der_public_key() and load_pem_public_key() functions do not verify that the point belongs to the expected prime-order subgroup of the curve. A remote attacker can provide a public key point P from a small-order subgroup. This can lead to security issues in various situations, such as the most commonly used signature verification (ECDSA) and shared key negotiation (ECDH). When the victim computes the shared secret as S = [victim_private_key]P via ECDH, this leaks information about victim_private_key mod (small_subgroup_order). For curves with cofactor > 1, this reveals the least significant bits of the private key. When these weak public keys are used in ECDSA , it's easy to forge signatures on the small subgroup.

How to mitigate CVE-2026-26007

Sources

• https://github.com/pyca/cryptography/commit/0eebb9dbb6343d9bc1d91e5a2482ed4e054a6d8c
• https://github.com/pyca/cryptography/security/advisories/GHSA-r6ph-v2qm-q3c2
• http://www.openwall.com/lists/oss-security/2026/02/10/4