CVE-2023-4807 is a high-severity vulnerability affecting the POLY1305 MAC implementation within the OpenSSL cryptographic library versions 1.1.1, 3.0.0, and 3.1.0. The flaw arises specifically on Windows 64-bit platforms running on newer x86_64 processors that support AVX512-IFMA instructions. The vulnerability is due to the POLY1305 MAC code failing to preserve the contents of non-volatile XMM registers during MAC calculation for data larger than 64 bytes. Instead of restoring these registers before returning control to the calling application, the implementation zeroizes them. Non-volatile XMM registers are expected by the Windows 64-bit ABI to be preserved across function calls, so this behavior violates expected calling conventions (CWE-440: Expected Behavior Violation). This register corruption can lead to unpredictable application behavior, including incorrect calculations, crashes, or denial of service. In the worst case, if the application relies heavily on these registers for critical state, it could lead to complete process control loss, although the attacker cannot inject arbitrary register values since they are zeroed out. The POLY1305 MAC is commonly used as part of the CHACHA20-POLY1305 AEAD cipher suite, which is widely employed in TLS 1.2 and TLS 1.3 protocols. A malicious client can influence the use of this AEAD cipher during TLS negotiation, potentially triggering the vulnerability on server applications using OpenSSL. However, no concrete exploit or affected application has been reported to date. The vulnerability can be mitigated by disabling AVX512-IFMA instruction support at runtime via the environment variable OPENSSL_ia32cap=:~0x200000. The FIPS provider in OpenSSL is not affected. This issue is specific to Windows 64-bit and newer processors with AVX512-IFMA support, limiting its scope. The CVSS v3.1 score is 7.8 (high), reflecting the potential for confidentiality, integrity, and availability impacts with low attack complexity but requiring local privileges and no user interaction.

For European organizations, the impact of CVE-2023-4807 depends on their use of OpenSSL versions 1.1.1, 3.0.0, or 3.1.0 on Windows 64-bit servers running on modern x86_64 CPUs with AVX512-IFMA support. Organizations operating TLS servers that allow CHACHA20-POLY1305 cipher suites could be vulnerable if a malicious client can influence cipher negotiation. Potential impacts include denial of service due to application crashes, incorrect cryptographic or application logic results, and in rare cases, full process compromise. This could affect critical infrastructure, web services, and internal applications relying on OpenSSL for secure communications. Given the vulnerability’s specificity to certain hardware and OS configurations, the overall risk is moderate but non-negligible for sectors with high security requirements such as finance, healthcare, and government. The inability to inject arbitrary register values reduces the likelihood of remote code execution but does not eliminate the risk of service disruption or data integrity issues. The lack of known exploits in the wild currently lowers immediate threat levels but organizations should proactively address the vulnerability to prevent future exploitation.

European organizations should take the following specific actions beyond generic patching advice: 1) Identify all Windows 64-bit systems running OpenSSL versions 1.1.1, 3.0.0, or 3.1.0 and verify if the underlying hardware supports AVX512-IFMA instructions. 2) For affected systems where immediate patching is not feasible, apply the recommended workaround by setting the environment variable OPENSSL_ia32cap=:~0x200000 to disable AVX512-IFMA support at runtime, preventing the vulnerable code path from executing. 3) Review TLS configurations to assess the use of CHACHA20-POLY1305 cipher suites and consider temporarily disabling them on vulnerable servers if risk tolerance is low. 4) Monitor application logs and system stability for signs of crashes or anomalies potentially related to this vulnerability. 5) Plan and prioritize upgrading OpenSSL to patched versions once available, ensuring compatibility testing on Windows 64-bit platforms with AVX512-IFMA CPUs. 6) Educate development and security teams about the subtle nature of ABI violations and encourage auditing of cryptographic code for similar issues. 7) For critical systems, consider isolating or limiting exposure to untrusted clients that could influence cipher negotiation. These targeted mitigations will reduce the attack surface and limit potential impacts while maintaining operational continuity.