Threats Tagged 'cve-2026-71891'

A vulnerability in Bouncy Castle for Java before version 1.86 allows acceptance of a public key constructed on a non-canonical elliptic curve that shares the BLS12-381 field characteristic but is not a valid G1 point. This flaw affects key validation in BLS12_381BasicScheme and related classes, enabling aggregate signature verification to accept signatures including phantom signers. The issue arises only if an application explicitly constructs ECPoints on non-canonical curves and accepts them as valid keys; the standard compressed-point decoder is unaffected.

CVE-2026-71891 is a high-severity vulnerability in Bouncy Castle for Java versions 1.85 up to but not including 1.86. It involves improper verification of cryptographic signatures due to acceptance of public keys constructed on non-canonical elliptic curves that share the field characteristic of BLS12-381 but differ in curve parameters. This flaw allows an attacker to create a phantom signer in aggregate signature verification, bypassing proper subgroup checks. The vulnerability is only exploitable if an application explicitly constructs ECPoints on non-standard curves and uses them as authority keys; the standard compressed-point decoder is unaffected. The issue has been addressed by adding strict validation of the curve parameters before subgroup checks.