CVE-2026-63410

{"id": "CVE-2026-63410", "cveTags": [], "metrics": {"cvssMetricV31": [{"type": "Secondary", "source": "security-advisories@github.com", "cvssData": {"scope": "UNCHANGED", "version": "3.1", "baseScore": 5.9, "attackVector": "NETWORK", "baseSeverity": "MEDIUM", "vectorString": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N", "integrityImpact": "NONE", "userInteraction": "NONE", "attackComplexity": "HIGH", "availabilityImpact": "NONE", "privilegesRequired": "NONE", "confidentialityImpact": "HIGH"}, "impactScore": 3.6, "exploitabilityScore": 2.2}]}, "affected": [{"source": "security-advisories@github.com", "affectedData": [{"vendor": "sgbett", "product": "secp256k1-native", "versions": [{"status": "affected", "version": ">= 0.17.0, < 0.18.0"}]}]}], "published": "2026-10-30T23:17:15.547", "references": [{"url": "https://github.com/sgbett/secp256k1-native/blob/master/docs/advisories/0001-compiler-reconstructed-ct-branch.md", "source": "security-advisories@github.com"}, {"url": "https://github.com/sgbett/secp256k1-native/commit/a89bea1617a2d063c6545ad44565dc22098c880e", "source": "security-advisories@github.com"}, {"url": "https://github.com/sgbett/secp256k1-native/pull/32", "source": "security-advisories@github.com"}, {"url": "https://github.com/sgbett/secp256k1-native/releases/tag/v0.18.0", "source": "security-advisories@github.com"}, {"url": "https://github.com/sgbett/secp256k1-native/security/advisories/GHSA-vp2j-gqfm-r3cf", "source": "security-advisories@github.com"}], "vulnStatus": "Received", "weaknesses": [{"type": "Primary", "source": "security-advisories@github.com", "description": [{"lang": "en", "value": "CWE-208"}, {"lang": "en", "value": "CWE-1255"}]}], "descriptions": [{"lang": "en", "value": "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."}], "lastModified": "2026-10-30T23:17:15.547", "sourceIdentifier": "security-advisories@github.com"}