CVE-2026-104421

6.9 mediumEPSS 0.3%

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.

CVSS 4.0: 6.9CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N
CVSS 3.1: 5.3CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
EPSS: 0.3% chance of exploitation in the next 30 days; higher than 22% of CVEs (scores of 2026-10-25)
CWE: CWE-459
Published: 2026-10-02
Modified: 2026-10-02
Record from: the NVD, synced 2026-10-19

References

https://github.com/ZcashFoundation/zebra/security/advisories/GHSA-x93j-mj2f-q338
https://www.vulncheck.com/advisories/zebra-before-6.2.1-block-download-denial-of-service-via-knownblock-senthashes-lockout

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