CVE-2022-4304 is a timing-based side channel vulnerability found in the RSA decryption implementation of OpenSSL versions 1.0.2, 1.1.1, and 3.0.0. The flaw affects all RSA padding modes including PKCS#1 v1.5, RSA-OAEP, and RSASVE. The vulnerability enables an attacker to perform a Bleichenbacher-style attack by sending a very large number of trial ciphertext messages to a target server and measuring the time taken to process each decryption attempt. By analyzing these timing differences, the attacker can gradually recover the plaintext of an encrypted message, such as the pre-master secret exchanged during a TLS handshake. This pre-master secret is critical as it is used to derive session keys for encrypting application data. Successfully recovering it would allow the attacker to decrypt the TLS session traffic, compromising confidentiality. The attack requires network access to the vulnerable server and the ability to send numerous decryption requests, which implies a high attack complexity. No authentication or user interaction is required, but the attacker must be able to observe timing with sufficient precision and send many requests. The vulnerability does not impact integrity or availability directly. Although no known exploits are currently reported in the wild, the potential for decrypting TLS sessions makes this a significant concern for any service relying on vulnerable OpenSSL versions for RSA-based key exchange. The CVSS v3.1 score is 5.9 (medium severity), reflecting the network attack vector, high complexity, no privileges or user interaction needed, and high impact on confidentiality only.

For European organizations, this vulnerability poses a risk to the confidentiality of sensitive communications protected by TLS using vulnerable OpenSSL versions with RSA key exchange. This includes web servers, mail servers, VPN gateways, and other network services that rely on OpenSSL for cryptographic operations. If exploited, attackers could decrypt intercepted TLS traffic, potentially exposing personal data, intellectual property, or confidential business communications. This is especially critical for sectors handling sensitive data such as finance, healthcare, government, and critical infrastructure. The attack requires a large volume of trial messages and precise timing measurements, which may limit feasibility in some environments but remains a realistic threat for high-value targets. The vulnerability does not affect the integrity or availability of systems but undermines trust in encrypted communications. Given the widespread use of OpenSSL across Europe and the reliance on TLS for secure communications, the potential impact is significant, particularly for organizations that have not yet upgraded to patched versions or migrated to safer key exchange methods like ECDHE.

1. Upgrade OpenSSL to the latest patched versions where this vulnerability is fixed. If immediate upgrade is not possible, consider applying any available vendor patches or workarounds. 2. Disable RSA key exchange in TLS configurations and prefer ephemeral Diffie-Hellman (ECDHE) key exchange methods, which are not affected by this vulnerability and provide forward secrecy. 3. Implement strict rate limiting and anomaly detection on TLS handshake requests to reduce the feasibility of large-scale trial message attacks. 4. Monitor network traffic for unusual patterns indicative of timing side channel probing attempts. 5. Use hardware security modules (HSMs) or cryptographic accelerators that implement constant-time RSA operations to mitigate timing leakage. 6. Conduct regular cryptographic audits and penetration tests to identify and remediate side channel vulnerabilities. 7. Educate security teams about side channel risks and ensure incident response plans include scenarios involving cryptographic key compromise.