CVE-2026-63076

Issue summary: OpenSSL CMP password based protection verification only

checks whether the protectionAlg parameter was not NULL and not its

ASN.1 type, before treating it as a PBMParameter. A crafted message can

contain a parameter of a different type, which is then dereferenced as an

invalid pointer.

Impact summary: A remote, unauthenticated attacker can crash an application

acting as a CMP server that accepts PBM-protected messages, or a CMP client

talking to a malicious or intercepted CMP server, resulting in a Denial of

Service.

CWE: CWE-476: NULL Pointer Dereference

Description: When verifying the password-based MAC protection of a CMP

message, OpenSSL library reads the protectionAlg algorithm parameter with

X509_ALGOR_get0(), which returns both the parameter type and its value

pointer. The value is then cast to an ASN1_STRING and treated as the

expected PBMParameter after only checking that pointer is not NULL. The

parameter type returned by X509_ALGOR_get0() was never consulted.

This happens during protection verification, before any MAC is computed, so

no knowledge of the PBM shared secret is required; the only precondition is

that PBM verification is reachable. On the server side this is reached from

OSSL_CMP_SRV_process_request() for any application that stands up a CMP

server accepting PBM-protected messages, and on the client side from CMP

response validation against a malicious or on-path (MITM) server. The

reliable consequence is a denial of service; there is no memory disclosure,

no controlled memory write, and no path to code execution. CMP is a

specialized feature that an application must explicitly enable.

FIPS impact: no

As the CMP code lives outside the FIPS module boundary, no FIPS modules

are affected by this CVE.