CVE-2026-63074 in OpenSSL
Summary
by MITRE • 08/25/2026
Issue summary: The OpenSSL Certificate Management Protocol (CMP) caches additional certificates (extraCerts) sent in a CMP message, but never expunges them (for instance if they are invalid). If a server reuses an OSSL_CMP_CTX frequently, this cache of extraCerts may grow unboundedly, and a malicious client may flood a CMP server with requests driving this growth.
Impact summary: Users utilizing a CMP server that reuses a single OSSL_CMP_CTX for the lifetime of a server process may observe unbounded memory growth in the event a malicious client repeatedly sends requests containing unique extra certificates, which may lead to OOM conditions.
CWE: CWE-770: Allocation of Resources Without Limits or Throttling
Description: If a remote user sends CMP messages to a server with a list of extraCerts and the message is rejected, the extraCerts from the message remains in the server contexts untrusted certificate stack. This exposes servers with long lived ctx objects to Denial of Service attacks in which an attacker sends messages intending to be rejected with a large list of additional certificates repeatedly, forcing the server to store them indefinitely. The issue was fixed by removing the added extra certs if the message is rejected, using the same method as when the context is configured to not do caching at all.
FIPS impact: no As the CMP code lives outside the FIPS module boundary, no FIPS modules are affected by this CVE.
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Analysis
by VulDB Data Team • 08/25/2026
The OpenSSL Certificate Management Protocol implementation contains a resource management flaw within its handling of additional certificates embedded in protocol messages. The vulnerability arises from the behavior of the OSSL_CMP_CTX structure when processing incoming CMP requests that include an extraCerts field. Under normal operational conditions, this context caches these supplementary certificates to facilitate efficient validation and chain building during subsequent interactions with the same client or certificate authority. However, the implementation fails to purge these cached entries if the associated message is ultimately rejected due to validation failures, syntax errors, or other policy violations. This design oversight means that any certificate included in a rejected request remains stored in the untrusted certificate stack of the server context indefinitely.
This flaw creates a significant security risk for servers configured to reuse a single OSSL_CMP_CTX instance across multiple requests over an extended period, which is a common pattern in long-running daemon processes or persistent service endpoints. A malicious actor can exploit this behavior by repeatedly sending CMP messages containing unique but invalid extra certificates. Since the server retains these entries regardless of the message outcome, each rejected request contributes to the accumulation of certificate objects in memory. Over time, and particularly under high-volume attack scenarios, this unbounded growth leads to excessive memory consumption. The situation is exacerbated if the attacker varies the content of the extraCerts field for each request, preventing any potential deduplication or caching efficiency that might otherwise limit storage requirements.
The operational impact of this vulnerability is primarily a Denial of Service condition resulting from resource exhaustion. As the cache expands without limit, the server process consumes increasing amounts of system memory until it reaches available limits. This can trigger Out-of-Memory conditions, causing the application to crash or become unresponsive to legitimate traffic. Such an attack vector allows remote adversaries to disrupt service availability with relatively low effort, requiring only the ability to send CMP messages and a target that maintains persistent context objects. The severity is heightened by the fact that this behavior occurs even when the message processing fails early in the validation pipeline, meaning attackers do not need successful authentication or valid credentials to trigger the memory leak.
From a classification perspective, this issue aligns with CWE-770, which describes the allocation of resources without proper limits or throttling controls. The failure to enforce size constraints on the certificate cache represents a classic instance of unbounded resource accumulation. In terms of attack taxonomy, this vulnerability supports techniques associated with Denial-of-Service attacks where adversaries aim to exhaust system resources rather than compromise confidentiality or integrity directly. It highlights the importance of implementing strict lifecycle management for cached data structures within network protocol handlers, ensuring that temporary state does not become permanent storage under error conditions.
The remediation strategy involves modifying the certificate handling logic to ensure that extra certificates are removed from the context if the associated message is rejected. This approach mirrors the behavior observed when caching is explicitly disabled, thereby preventing any persistent accumulation of invalid or unnecessary data. By cleaning up resources upon failure rather than retaining them indefinitely, the server maintains a bounded memory footprint regardless of the volume or nature of incoming requests. Administrators should ensure that their OpenSSL libraries are updated to include this fix, particularly if they operate CMP servers with long-lived context objects. Additionally, implementing general rate limiting and input validation at the network perimeter can provide defense-in-depth against such resource exhaustion attempts, although the core issue must be addressed in the library code itself for full protection.