The vulnerability (CVE-2026-54875) arises from a non-constant-time optimized scalar multiplication implementation used for SM2 private key operations on ARM64 and RISC-V processors. The implementation uses conditional branches and table lookups dependent on bits of the secret scalar, causing execution time and cache access patterns to leak information about the secret scalar during SM2 decryption or signature generation. This timing and cache side-channel can be exploited by attackers able to measure these characteristics. The issue affects OpenSSL versions 4.0, 3.6, 3.5, and 3.4 on the specified platforms, but not earlier versions 3.0, 1.1.1, or 1.0.2. Vendor fixes are available in the respective minor version updates.

An attacker capable of measuring timing or observing cache-line access patterns during SM2 signing or decryption on affected ARM64 or RISC-V platforms may gain partial information about the secret scalar used in the cryptographic operations. This could weaken the confidentiality of the private key or per-signature nonce. The impact is limited to information disclosure with no direct integrity or availability effects. The vulnerability does not affect FIPS modules as SM2 is not a FIPS algorithm.

Upgrading to the fixed OpenSSL versions is the recommended remediation: OpenSSL 4.0.3, 3.6.5, 3.5.9, or 3.4.8. Users of OpenSSL 4.0, 3.6, 3.5, and 3.4 on ARM64 or RISC-V platforms should apply these updates to mitigate the timing and cache side-channel vulnerability in SM2 private key operations. No other mitigations are specified by the vendor.