CVE-2026-77696 is a vulnerability in OpenSSL
Published on September 29, 2026
Timing Side-Channel in SM2 Signature Generation
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 Type
Observable Timing Discrepancy
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. In security-relevant contexts, even small variations in timing can be exploited by attackers to indirectly infer certain details about the product's internal operations. For example, in some cryptographic algorithms, attackers can use timing differences to infer certain properties about a private key, making the key easier to guess. Timing discrepancies effectively form a timing side channel.
Products Associated with CVE-2026-77696
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Affected Versions
OpenSSL:- Version 4.0.0 and below 4.0.3 is affected.
- Version 3.6.0 and below 3.6.5 is affected.
- Version 3.5.0 and below 3.5.9 is affected.
- Version 3.4.0 and below 3.4.8 is affected.
- Version 3.0.0 and below 3.0.23 is affected.
- Version 1.1.1 and below 1.1.1zj is affected.