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

Status: published. Published: 2026-09-29. Updated: 2026-11-10.

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.

## Remediation

- fix: The reporting source identifies this reference as a patch. Check the advisory for affected versions and supported release branches. (source: CNA: openssl) — https://github.com/openssl/openssl/commit/20b20628d39b2dcc4677194bd68c7c060fa598cb
- fix: The reporting source identifies this reference as a patch. Check the advisory for affected versions and supported release branches. (source: CNA: openssl) — https://github.com/openssl/openssl/commit/1c4aed808a7aea32d2d013049c2e0d9fef164fc9
- fix: The reporting source identifies this reference as a patch. Check the advisory for affected versions and supported release branches. (source: CNA: openssl) — https://github.com/openssl/openssl/commit/6b90445a56b99a328ac1feba058abf976504f440
- fix: The reporting source identifies this reference as a patch. Check the advisory for affected versions and supported release branches. (source: CNA: openssl) — https://github.com/openssl/openssl/commit/419f5cb519721dceed393dbc524d79e487c72e64

## Affected products and versions

- OpenSSL / OpenSSL: ≥ 4.0.0; < 4.0.3 (affected, semver); ≥ 3.6.0; < 3.6.5 (affected, semver); ≥ 3.5.0; < 3.5.9 (affected, semver); ≥ 3.4.0; < 3.4.8 (affected, semver); ≥ 3.0.0; < 3.0.23 (affected, semver); ≥ 1.1.1; < 1.1.1zj (affected, custom). Source: CNA: openssl
- Siemens / SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (6ES7518-4AX00-1AB0): ≥ V3.1.7; < * (affected, custom). Source: ADP: siemens-SADP
- Siemens / SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (6ES7518-4AX00-1AC0): ≥ V3.1.7; < * (affected, custom). Source: ADP: siemens-SADP
- Siemens / SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP (6ES7518-4FX00-1AB0): ≥ V3.1.7; < * (affected, custom). Source: ADP: siemens-SADP
- Siemens / SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP (6ES7518-4FX00-1AC0): ≥ V3.1.7; < * (affected, custom). Source: ADP: siemens-SADP
- Siemens / SIPLUS S7-1500 CPU 1518-4 PN/DP MFP (6AG1518-4AX00-4AC0): ≥ V3.1.7; < * (affected, custom). Source: ADP: siemens-SADP

## Severity and prioritization

- CVSS 3.1: 3.7 (low); CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N; source: ADP: CISA-ADP

- CISA KEV: No listing in collected sources

- EPSS: 0.40% as of 2026-11-09; percentile 34.11%

- SSVC: exploitation none; automatable no; technical impact partial; source ADP: CISA-ADP

- Weaknesses: CWE-208

## Exploit evidence

No exploit evidence in collected sources. This is not proof of no exploitation.

## References

- https://openssl-library.org/news/secadv/20260929.txt (CNA: openssl; vendor-advisory)

- https://github.com/openssl/openssl/commit/20b20628d39b2dcc4677194bd68c7c060fa598cb (CNA: openssl; patch)

- https://github.com/openssl/openssl/commit/1c4aed808a7aea32d2d013049c2e0d9fef164fc9 (CNA: openssl; patch)

- https://github.com/openssl/openssl/commit/6b90445a56b99a328ac1feba058abf976504f440 (CNA: openssl; patch)

- https://github.com/openssl/openssl/commit/419f5cb519721dceed393dbc524d79e487c72e64 (CNA: openssl; patch)

- https://cert-portal.siemens.com/productcert/html/ssa-457936.html (ADP: siemens-SADP)

## Provenance

- CNA: openssl: https://www.cve.org/CVERecord?id=CVE-2026-77696; retrieved 2026-11-10; source updated 2026-11-10

- FIRST EPSS: https://api.first.org/data/v1/epss?cve=CVE-2026-77696; retrieved 2026-11-10; source updated Not reported

Revision: dc0ea812d63ce8898063221f1109e32bf54b8c8fffd67e5d12c58c2de6f83c31

Canonical: https://y2.dev/cve/CVE-2026-77696

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