CVE-2024-4603

What it actually does

The EVP_PKEY_param_check and EVP_PKEY_public_check functions perform unbounded modular arithmetic on DSA p parameters, allowing an attacker-supplied modulus larger than 10000 bits to trigger prolonged computation and CPU exhaustion.

Why it matters to the business

Applications that directly validate DSA keys or parameters from external sources can experience extended processing delays, resulting in service degradation or temporary unavailability without affecting core TLS operations.

How an attack unfolds

An attacker crafts a DSA key or parameter set containing an excessively large modulus and supplies it to an application that invokes EVP_PKEY_param_check or EVP_PKEY_public_check on untrusted input; the check routines consume significant CPU time before returning, producing a denial-of-service condition.

How to fix it

Upgrade OpenSSL to the version containing commit 3559e868e58005d15c6013a0c1fd832e51c73397. Applications should avoid calling the affected check functions on untrusted input until patched; command-line usage of openssl pkey -check and pkeyparam -check should be restricted to trusted material.

How to confirm the fix worked

Confirm the installed OpenSSL library reports a version that includes commit 3559e868e58005d15c6013a0c1fd832e51c73397; recompile dependent applications against the fixed library and verify that large-DSA check operations complete promptly or are rejected early.

Typical attack path

1. Identify an application that calls EVP_PKEY_param_check or EVP_PKEY_public_check on externally supplied DSA material
2. Generate a DSA parameter structure with a modulus exceeding 10000 bits
3. Deliver the malformed key or parameters through the application's input channel
4. Trigger the check function and observe sustained high CPU usage on the target process

How to detect it

Review application and system logs for unusually long execution times or high CPU attributed to DSA key or parameter validation routines; correlate with inbound network traffic containing large ASN.1 structures.

What your security team should do

• Apply the patch containing commit 3559e868e58005d15c6013a0c1fd832e51c73397 to all OpenSSL 3.0 and 3.1 deployments
• Audit source code for direct calls to EVP_PKEY_param_check and EVP_PKEY_public_check on untrusted data
• Disable or sandbox the openssl pkey -check and pkeyparam -check options in environments that process external keys
• Monitor CPU utilization on processes that perform DSA parameter validation