CVE-2026-104421

Zebra before 6.2.1 Block Download Denial of Service via KnownBlock SentHashes Lockout

State: Published
Severity: 6.9 Medium
Published: Oct 2, 2026
Updated: Oct 2, 2026
Reserved: Oct 2, 2026

Description

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.

Scores

CVSS	Score	Vector	Source
4.0	6.9 Medium	CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N	VulnCheck
3.1	5.3 Medium	CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L	VulnCheck

Weaknesses

CWE-459 Incomplete Cleanup

Affected Products

Product	Versions
zebraZcashFoundation	before 6.2.1Affected 6.2.1Not affected

References

GitHub Security Advisory (GHSA-x93j-mj2f-q338)vendor-advisory
VulnCheck Advisory: Zebra before 6.2.1 Block Download Denial of Service via KnownBlock SentHashes Lockoutthird-party-advisory

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