CVE-2026-63410

MEDIUMPre-NVD 5.95.9
EchelonGraph scoreMEDIUM confidence

“—” beside the score: it is equal to the CVSS score beside it.

This medium-severity CVE scores 5.9 under the CNA's CVSS (NVD's own analysis pending). EPSS exploit probability: 0.3% (20th percentile of EPSS-scored CVEs). No GitHub Security Advisory CVSS is on record for this CVE.

Triggered by: Headline CVSS from the CNA's CVSS
Sources: the CNA's CVSS, EPSS
Trending — 4 sources updated this weekElevated

Also known asEUVD-2026-114552 (ENISA EUVD)Source: ENISA EUVD

5.9EG
EchelonGraph verdictPlan a fixRemediate within your standard update timelines (the SSVC decision on this page).
  • CISA's Vulnrichment rates exploitation as PoC; EchelonGraph holds no exploit-code reference for it
CISA-KEV: Not listedEPSS PROB: 0.3%CVSS: 5.9Exploit: No code on recordExposed services: Not assessed

A fix is available — apply it.

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.

CVSS v3
5.9
EG Score
5.9MEDIUMmedium confidence
EG Risk
43
EG Risk 43/100

EG Risk is EchelonGraph's 0–100 priority score. It fuses impact severity (EG Severity, the CVSS base score, never the KEV-floored or EPSS-lifted EG Score) with real-world exploitation and automatability, under weights EchelonGraph set by hand, so you can rank equal-severity CVEs and fix the most dangerous first. Higher = act sooner.

How it’s computed (value × EchelonGraph’s weight)
Severity59% × 45%
Impact severity (EG Severity): CVSS 5.9 of 10. Never the KEV-floored or EPSS-lifted EG Score.
Exploitation40% × 40%
EchelonGraph's fixed weight for EG-KEV Tier 3 (Elevated): a constant, not a probability.
Automatability0% × 15%
CISA's SSVC Automatable value: no (Vulnrichment).
SSVC (CISA's decision table, applied by EchelonGraph): Track at low or medium mission impact; Track* at high (mission-essential systems).
Exploitation public PoC (CISA Vulnrichment) · Automatable no (CISA Vulnrichment) · Technical impact partial (CISA Vulnrichment). All three are CISA's SSVC values (Vulnrichment). EchelonGraph applied CISA's decision table to them; CISA publishes SSVC inputs and the table, not a decision for each CVE.
Action: A fix is available. Apply it within your standard update timelines.
EPSS PROB
0.3%
EPSS %ILE
20th
KEV
Not listed

What the EG score is made of (scorer v4.0: the three questions the 0–10 score mixes, published apart · methodology)

The EG score (5.9): severity, escalated by confirmed exploitation. This CVE's 5.9 is its impact severity (EG Severity), not escalated.

EG Severity
5.9 MEDIUMCVSS-B, impact only: no KEV listing, EPSS or EG-KEV tier raises it.the CNA's CVSS · CVSS v3.0 or v3.1
EG Likelihood
0.3% within 30 daysSource: FIRST EPSS (model v2026.06.15, score date 2026-11-01). FIRST's exploitation probability, not an EchelonGraph model.
Confirmed exploitation
None on record (CISA KEV, EG-KEV Tier 1)Reported apart from the likelihood: an observed fact, not a probability.
EG Priority
SSVC Track at medium mission impactTrack at low or medium mission impact; Track* at high (mission-essential systems).CISA BOD 26-04: 60 days if the affected system is publicly exposed; Fix on system upgrade if it is not.Each input and its source, and whom BOD 26-04 binds: the SSVC and BOD 26-04 blocks below.

SSVC (CISA's decision table, applied by EchelonGraph)Track at low or medium mission impact; Track* at high (mission-essential systems).

A fix is available. Apply it within your standard update timelines.

Exploitation public PoC (CISA Vulnrichment) · Automatable no (CISA Vulnrichment) · Technical impact partial (CISA Vulnrichment). All three are CISA's SSVC values (Vulnrichment). EchelonGraph applied CISA's decision table to them; CISA publishes SSVC inputs and the table, not a decision for each CVE. Mission impact is CISA's Mission & Well-being decision point, and only you can judge it. CISA's table makes it high when Mission Prevalence is Essential — the vulnerable component "directly provides capabilities that constitute at least one MEF for at least one entity" (MEF: mission essential function) — or when Public Well-Being Impact is Irreversible: "multiple fatalities are likely", the cyber-physical system "is likely lost or destroyed", "extreme or serious externalities" are imposed on other parties, or social systems such as elections or the financial grid "are destabilized and potentially collapse". CISA's decision table

BOD 26-04 (CISA's remediation timeline, Table 1)60 days if the affected system is publicly exposed; Fix on system upgrade if it is not.

The score's inputs: In CISA KEV no (CISA's KEV catalog) · Automatable no (CISA Vulnrichment) · Technical impact partial (CISA Vulnrichment). Whether your system is publicly exposed is yours to answer. BOD 26-04 binds US Federal Civilian Executive Branch agencies; for anyone else it is CISA's published timeline, a reference rather than an obligation. The directive · how EchelonGraph applies it

Published

October 30, 2026

Last Modified

November 2, 2026

Advisory Details (5)

Auto-updated Oct 30, 2026
Patch available. Sources: github, github_pr, github_commit, github_release.
GitHub release Patch Available

secp256k1-native 0.18.0 — security release (GHSA-vp2j-gqfm-r3cf)

Patch available: sgbett/secp256k1-native v0.18.0

https://github.com/sgbett/secp256k1-native/releases/tag/v0.18.0
Web page

secp256k1-native/docs/advisories/0001-compiler-reconstructed-ct-branch.md at master · sgbett/secp256k1-native · GitHub

https://github.com/sgbett/secp256k1-native/blob/master/docs/advisories/0001-compiler-reconstructed-ct-branch.md
GitHub commit Patch Available

commit a89bea1617a2 (sgbett/secp256k1-native)

Patch available: sgbett/secp256k1-native v0.18.0 (contains commit a89bea1617a2)

https://github.com/sgbett/secp256k1-native/commit/a89bea1617a2d063c6545ad44565dc22098c880e
GitHub pull request Patch Available

fix(ct): block GCC-reconstructed branch in constant-time selects (#25 bare-metal finding)

Patch available: sgbett/secp256k1-native v0.18.0 (PR #32 merged 2026-06-30)

https://github.com/sgbett/secp256k1-native/pull/32
GitHub advisoryMentions a patch (unverified)

GCC 14/15 at -O2 reconstructs the branchless uint256_select idiom in Point#mul (Montgomery-ladder secret-scalar path) into a secret-dependent conditional jump, leaking the secret scalar. · Advisory · sgbett/secp256k1-native · GitHub

https://github.com/sgbett/secp256k1-native/security/advisories/GHSA-vp2j-gqfm-r3cf

Weakness Classification(2)

MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.

Data Freshness Timeline

(refreshed 8× in last 7d / 8× in last 30d)

Each row is a time one of our pipelines fetched, updated or re-scored this CVE. For example, "NVD update" means NVD published or revised its analysis for this CVE; "MITRE cvelistV5" means we ingested or refreshed it from the CNA feed. An arrow marks a change the record states ("CVSS v3 → 9.1"); EPSS and GHSA rows show the values recorded at that time, not what changed (EPSS values are rounded; hover one for the exact figures). Most recent first.

  1. 2026-11-02 16:45 UTCEPSS rescoreEPSS 0.3% · 20th percentile
  2. 2026-11-02 15:26 UTCEG score recompute
  3. 2026-11-02 14:58 UTCEG score recompute
  4. 2026-10-31 16:33 UTCEPSS rescoreEPSS 0.3% · 20th percentile
  5. 2026-10-31 00:02 UTCENISA EUVD ID recordedEUVD-2026-114552 · Source: ENISA EUVD
  6. 2026-10-30 23:26 UTCEG score recompute
  7. 2026-10-30 22:54 UTCEG score recomputeFirst assessed: 5.9 MEDIUM
  8. 2026-10-30 22:53 UTCMITRE cvelistV5first tracked

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Frequently asked(5)

What is CVE-2026-63410?
CVE-2026-63410 is a medium-severity vulnerability; its CVE record was published on October 30, 2026. 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…
When was the CVE record for CVE-2026-63410 published?
The CVE record for CVE-2026-63410 was published on October 30, 2026. That is the record's publication date; the vulnerability itself may have been made public earlier. EchelonGraph's copy of the record carries a last-modified date of November 2, 2026; the record at its source may have been updated since.
Is CVE-2026-63410 actively exploited?
CVE-2026-63410 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 0.3% probability of exploitation in the next 30 days (20th percentile of EPSS-scored CVEs).
What is the CVSS score of CVE-2026-63410?
CVE-2026-63410 has a CVSS base score of 5.9 (a secondary CVSS source that NVD displays; NVD's own analysis pending).
How do I remediate CVE-2026-63410?
A fix for CVE-2026-63410 is available: update to the fixed version the vendor names in its advisory.

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