CVE-2026-71891
Description
A flaw was found in Bouncy Castle. When validating Boneh-Lynn-Shacham (BLS) signature public keys, the library does not verify that a key is constructed on the canonical elliptic curve. An attacker can exploit this issue by supplying a specially crafted public key defined on an alternate curve. This flaw allows an attacker to bypass cryptographic signature checks, enabling aggregate signatures to be accepted without legitimate signing.
Statement
This vulnerability is rated as Moderate severity for Red Hat products because exploitation requires uncommon application-level conditions where public keys are instantiated on custom, non-canonical curves instead of standard encoded formats. Normal signature processing using standard serialized key formats is not impacted. Consequently, standard deployments are unlikely to be exposed to signature verification bypass unless specialized key-generation logic is implemented.
Understanding the Weakness (CWE)
Access Control,Integrity,Confidentiality
Technical Impact: Gain Privileges or Assume Identity; Modify Application Data; Execute Unauthorized Code or Commands
An attacker could gain access to sensitive data and possibly execute unauthorized code.
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