CVE-2026-63076: Invalid Pointer Dereference in CMP Server via Crafted protectionAlg

Severity: high (CVSS 7.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 1.6% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-08-25 · updated 2026-09-11
Weakness: CWE-476

Description

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.

Affected products

OpenSSL: from 3.0.0 before 3.0.22; from 3.4.0 before 3.4.7; from 3.5.0 before 3.5.8; from 3.6.0 before 3.6.4; from 4.0.0 before 4.0.2 — fixed in 3.0.22, 3.4.7, 3.5.8, 3.6.4, 4.0.2

How to fix

Upgrade to a fixed version: OpenSSL 3.0.22, 3.4.7, 3.5.8, 3.6.4. Check the vendor advisory for mitigations.

References

Get alerted when CVE-2026-63076 or the next vulnerability affects your stack