What’s Vulnerable › Vulnerabilities

CVE-2026-77696: Timing Side-Channel in SM2 Signature Generation

• Severity: low (CVSS 3.7 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.4% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-09-29 · updated 2026-10-08
• Weakness: CWE-208

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.

Affected products

• OpenSSL: from 1.1.1 before 1.1.1zj; from 3.0.0 before 3.0.23; from 3.4.0 before 3.4.8; from 3.5.0 before 3.5.9; from 3.6.0 before 3.6.5; from 4.0.0 before 4.0.3 — fixed in 1.1.1zj, 3.0.23, 3.4.8, 3.5.9, 3.6.5, 4.0.3

How to fix

Upgrade to a fixed version: OpenSSL 1.1.1zj, 3.0.23, 3.4.8, 3.5.9. Check the vendor advisory for mitigations.

References

• https://github.com/openssl/openssl/commit/1c4aed808a7aea32d2d013049c2e0d9fef164fc9
• https://github.com/openssl/openssl/commit/20b20628d39b2dcc4677194bd68c7c060fa598cb
• https://github.com/openssl/openssl/commit/419f5cb519721dceed393dbc524d79e487c72e64
• https://github.com/openssl/openssl/commit/6b90445a56b99a328ac1feba058abf976504f440
• https://openssl-library.org/news/secadv/20260929.txt

Get alerted when CVE-2026-77696 or the next vulnerability affects your stack