secp256k1-native: Compiler-reconstructed secret-dependent branch in native scalar multiplication
Summary
| CVE | CVE-2026-63410 |
|---|---|
| State | PUBLISHED |
| Assigner | GitHub_M |
| Source Priority | CVE Program / NVD first with legacy fallback |
| Published | 2026-10-30 23:17:15 UTC |
| Updated | 2026-11-02 19:35:33 UTC |
| Description | 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. |
Risk And Classification
Primary CVSS: v3.1 5.9 MEDIUM from [email protected]
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N
EPSS: 0.002810000 probability, percentile 0.206360000 (date 2026-11-02)
Problem Types: CWE-208 | CWE-1255 | CWE-208 CWE-208: Observable Timing Discrepancy | CWE-1255 CWE-1255: Comparison Logic is Vulnerable to Power Side-Channel Attacks
| Version | Source | Type | Score | Severity | Vector |
|---|---|---|---|---|---|
| 3.1 | [email protected] | Secondary | 5.9 | MEDIUM | CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N |
| 3.1 | CNA | DECLARED | 5.9 | MEDIUM | CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N |
CVSS v3.1 Breakdown
Attack Vector
NetworkAttack Complexity
HighPrivileges Required
NoneUser Interaction
NoneScope
UnchangedConfidentiality
HighIntegrity
NoneAvailability
NoneCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N
Vendor Declared Affected Products
| Source | Vendor | Product | Version | Platforms |
|---|---|---|---|---|
| CNA | Sgbett | Secp256k1-native | affected >= 0.17.0, < 0.18.0 | Not specified |
References
| Reference | Source | Link | Tags |
|---|---|---|---|
| github.com/sgbett/secp256k1-native/blob/master/docs/advisories/0001-comp... | [email protected] | github.com | |
| github.com/sgbett/secp256k1-native/pull/32 | [email protected] | github.com | |
| github.com/sgbett/secp256k1-native/commit/a89bea1617a2d063c6545ad44565dc... | [email protected] | github.com | |
| github.com/sgbett/secp256k1-native/releases/tag/v0.18.0 | [email protected] | github.com | |
| github.com/sgbett/secp256k1-native/security/advisories/GHSA-vp2j-gqfm-r3cf | 134c704f-9b21-4f2e-91b3-4a467353bcc0 | github.com | |
| CVE Program record | CVE.ORG | www.cve.org | canonical |
| NVD vulnerability detail | NVD | nvd.nist.gov | canonical, analysis |
No vendor comments have been submitted for this CVE.
There are currently no legacy QID mappings associated with this CVE.