CVE-2026-77696

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.

Weakness

Two separate operations in a product require different amounts of time to complete, in a way that is observable to an actor and reveals security-relevant information about the state of the product, such as whether a particular operation was successful or not.

Affected Software

Related Attack Patterns

• https://cwe.mitre.org/data/definitions/462.html
• https://cwe.mitre.org/data/definitions/541.html
• https://cwe.mitre.org/data/definitions/580.html

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