CVE-2026-77696

OpenSSL’s SM2 implementation performs arithmetic on secret values with variable time; the time taken to produce a signature leaks information about the nonce and private key. An attacker who can observe many signing operations can use this timing data to mount a lattice or Hidden Number Problem attack that eventually recovers the private key. The flaw is a timing side‑channel (CWE‑208). The vulnerability does not affect FIPS compliance because SM2 is not a FIPS algorithm.

The vulnerability affects all OpenSSL releases that build SM2 signature code with non‑constant‑time arithmetic. All platforms using the affected OpenSSL binaries are impacted; no specific version range is listed, so the risk applies until the code is patched.

The CVSS score is 3.7, indicating low severity, and there is no EPSS information or KEV listing. The likely attack vector is inferred to be remote or local environments where an attacker can observe signing times, such as over a network or via a shared device. While the vulnerability is low‑severity, the potential to recover a private key makes it serious for operations that heavily rely on SM2 signatures.