All vulnerabilities
CVE-2026-77696

OpenSSL: Timing Side-Channel in SM2 Signature Generation

OpenSSL OpenSSLLibraries & packages
Open in ThreatlineRecord JSON
CVSS
3.7Low
ExploitationNo known exploitationNot in CISA KEV, which does not prove it is unexploitedCISA KEV
Exploit odds (EPSS)0.24%Chance of exploitation activity in the next 30 days, higher than 14% of CVEs. Scored 23 Oct 2026FIRST EPSS
Fixed in4.0.3Also 3.6.5, 3.5.9 and 3 moreCVE List
Published29 Sep 2026Updated 29 Sep 2026CVE List

What fixes it

A fixed version on one release line is not the upgrade target for every line. Check your exact version and any vendor backports.

Description

Issue summary: SM2 signature generation uses non-constant-time arithmetic on secret values, forming a timing side-channel.

Impact summary: An attacker able to measure SM2 signing times may learn information about the per-signature secret nonce, which over many signatures can, via a lattice / Hidden Number Problem attack, lead to recovery of the private key.

CWE: CWE-208: Observable Timing Discrepancy

Description: SM2 signature generation computes the signature value using variable-time BIGNUM operations on the secret nonce and the private key, so the time taken to produce an SM2 signature depends on these secret values, forming a timing side-channel.

Applications performing SM2 signature generation are affected on all platforms.

FIPS Impact: no SM2 is not a FIPS algorithm.

Text from CVE List

Affected versions 6

  • OpenSSLaffected: 4.0.0 before 4.0.3CVE List
  • OpenSSLaffected: 3.6.0 before 3.6.5CVE List
  • OpenSSLaffected: 3.5.0 before 3.5.9CVE List
  • OpenSSLaffected: 3.4.0 before 3.4.8CVE List
  • OpenSSLaffected: 3.0.0 before 3.0.23CVE List
  • OpenSSLaffected: 1.1.1 before 1.1.1zjCVE List

References 5