# CVE-2026-123555: Zebra 2.3.0 before 7.0.0 Denial of Service via Unscored Script Verification Failures

Status: published. Published: 2026-11-08. Updated: 2026-11-13.

Zebra from 2.3.0 before 7.0.0 contains a denial of service vulnerability that allows unauthenticated peers to evade misbehavior scoring by sending transactions or blocks with invalid transparent scripts. Attackers can flood mempool with script-failing transactions or serve forged v5 block bodies with altered scriptSig bytes to exhaust CPU and repeatedly stall block sync.

## Remediation

- fix: The reporting source identifies this reference as a patch. Check the advisory for affected versions and supported release branches. (source: CNA: VulnCheck) — https://github.com/ZcashFoundation/zebra/commit/e8db87eb69254e0d4eedd058eadd48bdfa09065a

## Affected products and versions

- ZcashFoundation / zebra (zebrad): ≥ 2.3.0; < 7.0.0 (affected, semver); 7.0.0 (unaffected, semver). Source: CNA: VulnCheck
- ZcashFoundation / zebra (zebra-consensus): ≥ 1.0.0-beta.46; < 18.0.0 (affected, semver); 18.0.0 (unaffected, semver). Source: CNA: VulnCheck

## Severity and prioritization

- CVSS 4.0: 8.7 (high); CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N; source: CNA: VulnCheck

- CVSS 3.1: 7.5 (high); CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H; source: CNA: VulnCheck

- CVSS 4.0: 8.7 (high); CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X; source: NVD: disclosure@vulncheck.com

- CVSS 3.1: 7.5 (high); CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H; source: NVD: disclosure@vulncheck.com

- CISA KEV: No listing in collected sources

- EPSS: 0.43% as of 2026-11-12; percentile 37.88%

- SSVC: exploitation none; automatable yes; technical impact partial; source ADP: CISA-ADP

- Weaknesses: CWE-755

## Exploit evidence

No exploit evidence in collected sources. This is not proof of no exploitation.

## References

- https://github.com/ZcashFoundation/zebra/security/advisories/GHSA-jq45-ghw5-v37x (CNA: VulnCheck; vendor-advisory)

- https://github.com/ZcashFoundation/zebra/commit/e8db87eb69254e0d4eedd058eadd48bdfa09065a (CNA: VulnCheck; patch)

- https://www.vulncheck.com/advisories/zebra-2.3.0-before-7.0.0-denial-of-service-via-unscored-script-verification-failures (CNA: VulnCheck; third-party-advisory)

- https://github.com/ZcashFoundation/zebra/commit/e8db87eb69254e0d4eedd058eadd48bdfa09065a (disclosure@vulncheck.com)

- https://github.com/ZcashFoundation/zebra/security/advisories/GHSA-jq45-ghw5-v37x (disclosure@vulncheck.com)

- https://www.vulncheck.com/advisories/zebra-2.3.0-before-7.0.0-denial-of-service-via-unscored-script-verification-failures (disclosure@vulncheck.com)

## Provenance

- CNA: VulnCheck: https://www.cve.org/CVERecord?id=CVE-2026-123555; retrieved 2026-11-13; source updated 2026-11-13

- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-123555; retrieved 2026-11-08; source updated 2026-11-08

- FIRST EPSS: https://api.first.org/data/v1/epss?cve=CVE-2026-123555; retrieved 2026-11-13; source updated Not reported

Revision: 36b33e3fd4cdf8a4175a155400fd76b1e52884072fb83d6a2e2b2dcb6da4e360

Canonical: https://y2.dev/cve/CVE-2026-123555

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