CVE-2026-77696 (CVSS 3.7)

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.

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CVSS v3.1 Score

3.7

LOW

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N

EPSS — Exploit Prediction

0.0024

Probability of exploitation

0.14%

Percentile rank

EPSS estimates the probability that this vulnerability will be exploited in the wild within the next 30 days. A higher score means more likely to be exploited.

Weakness Type (CWE)

CWE-208 CWE-208

References

Other 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

Frequently Asked Questions

What is 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. It has a CVSS v3.1 base score of 3.7 (LOW).

How severe is CVE-2026-77696? +

CVE-2026-77696 has a CVSS v3.1 score of 3.7 out of 10, rated LOW. This is a low-severity vulnerability with limited impact. The EPSS score is 0.0024, placing it in the 0th percentile for exploitation probability.

How do I check if I'm vulnerable to CVE-2026-77696? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

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