CVE-2026-104421

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

Published Oct 2, 2026 CVSS 4.0 · 6.9 Medium EPSS < 1% KEV · Not listed
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.

Remediation

No solution or workaround provided in the CVE record

Tracking

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Advisories

No advisories available
History
Type Values Removed Values Added
First Time appeared Zcashfoundation
Zcashfoundation zebra
Vendors & Products Zcashfoundation
Zcashfoundation zebra
Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'yes', 'Exploitation': 'none', 'Technical Impact': 'partial'}, 'version': '2.0.3'}

Type Values Removed Values Added
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.
Title Zebra before 6.2.1 Block Download Denial of Service via KnownBlock SentHashes Lockout
First Time appeared Zfnd
Zfnd zebra
Weaknesses CWE-459
CPEs cpe:2.3:a:zfnd:zebra:*:*:*:*:*:*:*:*
Vendors & Products Zfnd
Zfnd zebra
References
Metrics cvssV3_1

{'score': 5.3, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L'}

cvssV4_0

{'score': 6.9, 'vector': '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'}

Weaknesses

Sources

Status
PUBLISHED
Assigner
VulnCheck
Published
Updated
Oct 2, 2026, 12:28 PM
Reserved
Oct 2, 2026, 12:46 AM
Status
Deferred
Published
Oct 2, 2026, 12:17 PM
Modified
Oct 2, 2026, 5:59 PM