CVE-2024-41996: 
OpenSSL vulnerability analysis and mitigation

CVE-2024-41996 is a vulnerability in the Diffie-Hellman Ephemeral (DHE) Key Agreement Protocol discovered in August 2024. The vulnerability allows remote attackers from the client side to trigger unnecessarily expensive server-side DHE modular-exponentiation calculations when an approved safe prime is used. The basic attack scenario requires the client to claim it can only communicate with DHE, and the server must be configured to allow DHE and validate the order of the public key (NVD, DHEat Details).

The vulnerability exploits the peculiarity of the Diffie-Hellman key agreement where a malicious client can force a server to perform CPU-intensive operations without any significant resource requirement. The attack works by having the client initiate cryptographic handshakes while pretending to support only the ephemeral variant of the finite field Diffie-Hellman key agreement protocol. This triggers key pair generation and shared secret calculation on the server-side, both requiring compute-intensive modular exponentiation calculations. The server cannot distinguish between a randomly chosen number and the result of modular exponentiation without performing CPU-intensive operations (DHEat Details).

The vulnerability can lead to asymmetric resource consumption, potentially resulting in a denial of service condition. When exploited, it causes the server to perform unnecessarily expensive calculations while the attacker requires minimal computational resources. The effectiveness of the attack can be particularly severe when servers use larger parameter sizes (e.g., ffdhe6144 or ffhde8192) or when certain implementation flaws are present (DHEat FAQ).

Detection of exploitation is possible through monitoring and logging of instances where client connections are interrupted during cryptographic handshakes. While disabling Diffie-Hellman in server configurations is not necessarily required, administrators should check both server configuration and cryptographic library implementation details. The vulnerability cannot be fixed by simply installing a software update as it is a protocol flaw rather than an implementation issue (DHEat FAQ).