CVE-2026-63410
MediumCVSS 5.9Exploitation Probability (EPSS)
Low risk21th percentile - higher than 21% of all known CVEs
Summary
A vulnerability in secp256k1-native (native C implementation for Ruby) causes GCC 14.3.0, 15.1.0, and 15.2.0 at -O2 to reconstruct branchless selections into conditional jumps (je/jne), leaking timing information about the secret scalar. The flaw affects native builds, not the pure-Ruby path.
Risk Assessment
An attacker able to repeatedly measure timing of point multiplication can statistically recover bits of a secret private key or nonce, leading to cryptographic key compromise.
Recommendation
Upgrade secp256k1-native to version 0.18.0, which contains the verified fix, or rebuild with a toolchain that does not reconstruct branches (e.g., GCC 13.3.0 or newer with appropriate flags).
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Original NVD description (English source)
secp256k1-native is a native C secp256k1 implementation for Ruby. In affected native builds, native constant-time scalar multiplication through `Point#mul` or `scalar_multiply_ct` can leak timing information about a secret scalar when compiled by a toolchain that reconstructs branchless selection into a branch. The `Montgomery ladder` uses `uint256_select` with an all-zeros or all-ones mask, but affected GCC builds at `-O2` recover the original condition and emit secret-dependent `je` or `jne` jumps whose timing correlates with scalar bits. This defeats the assumption behind the 0.17.0 `jp_add_internal` infinity-branch fix. A consumer must multiply a secret private key or nonce in a context where an attacker can observe timing; repeated measurements can statistically recover scalar bits. The defect is in the compiled binary, so source review or `ctgrind` on a non-reconstructing toolchain may miss it. GCC 14.3.0, 15.1.0, and 15.2.0 reproduced the branch reconstruction, and `extconf.rb` appends `-O2`. Tested GCC versions through 12.4.0 used bitwise operations and GCC 13.3.0 used constant-time `cmov`; the pure-Ruby path is not affected by this flaw and separately makes no constant-time claim. GCC 16 and clang were untested, and point releases, targets, and flag combinations were not exhaustively bisected. `Earlier pre-0.17.0 versions had different constant-time issues rather than this introduced select idiom.` Version 0.18.0 contains the verified fix. The advisory's broad pre-0.18.0 guidance also covers earlier, different constant-time issues; whether this CVE groups those issues or only the select idiom introduced in 0.17.0 remains unresolved.
Vulnerability data from NVD (NIST) · CISA KEV · EPSS