Issue summary: A timing side-channel which could potentially allow recovering
the private key exists in the ECDSA signature computation.

Impact summary: A timing side-channel in ECDSA signature computations
could allow recovering the private key by an attacker. However, measuring
the timing would require either local access to the signing application or
a very fast network connection with low latency.

There is a timing signal of around 300 nanoseconds when the top word of
the inverted ECDSA nonce value is zero. This can happen with significant
probability only for some of the supported elliptic curves. In particular
the NIST P-521 curve is affected. To be able to measure this leak, the attacker
process must either be located in the same physical computer or must
have a very fast network connection with low latency. For that reason
the severity of this vulnerability is Low.

CWE-385

https://github.com/openssl/openssl/commit/07272b05b04836a762b4baa874958af51d513844

https://github.com/openssl/openssl/commit/2af62e74fb59bc469506bc37eb2990ea408d9467

https://github.com/openssl/openssl/commit/392dcb336405a0c94486aa6655057f59fd3a0902

https://github.com/openssl/openssl/commit/4b1cb94a734a7d4ec363ac0a215a25c181e11f65

https://github.com/openssl/openssl/commit/77c608f4c8857e63e98e66444e2e761c9627916f

https://github.openssl.org/openssl/extended-releases/commit/0d5fd1ab987f7571e2c955d8d8b638fc0fb54ded

https://github.openssl.org/openssl/extended-releases/commit/a2639000db19878d5d89586ae7b725080592ae86

https://openssl-library.org/news/secadv/20250120.txt