What is CVE-2026-104421?

CVE-2026-104421 is a medium-severity vulnerability in Zcashfoundation Zebra, classified under Incomplete Cleanup. CVSS score: 5.3/10. Published 2026-10-02.

How severe is CVE-2026-104421?

Medium severity. CVSS v3 base score is 5.3 out of 10.

Vulnerability in Zcashfoundation Zebra

CVE-2026-104421

Zebra before 6.2.1 contains an incomplete cleanup vulnerability that allows unauthenticated peers to block downloading of valid blocks by leaving rejected hashes in SentHashes. Attackers can send a contextually invalid block sharing an honest block's header hash, causing Request::KnownBlock to skip the honest block and keep nodes behind the tip.

Published 2026-10-02 · last modified 2026-10-02.

CVSS v3 metric

CVSS v3 base score 5.3 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L.

EPSS exploit prediction

No EPSS score from FIRST.org yet. New CVEs usually get one within a few days; no score means no signal yet, not low risk. How EPSS works.

Affected products

Zcashfoundation Zebra

Weakness classification (CWE)

CWE-459 — Incomplete Cleanup

References

github.com/ZcashFoundation/zebra/security/advisories/GHSA-x93j-mj2f-q338 (vendor-advisory)
www.vulncheck.com/advisories/zebra-before-6.2.1-block-download-denial-of-servic… (third-party-advisory)

Frequently asked questions

What is CVE-2026-104421?: CVE-2026-104421 is a medium-severity vulnerability in Zcashfoundation Zebra, classified under Incomplete Cleanup. CVSS score: 5.3/10. Published 2026-10-02.
How severe is CVE-2026-104421?: Medium severity. CVSS v3 base score is 5.3 out of 10.