Medium severity · published Oct 2, 2026
CVE-2026-104421
Zebra before 6.2.1 Block Download Denial of Service via KnownBlock SentHashes Lockout
5.3
CVSS
0.3%
EPSS
No
On KEV
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.
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Confidentiality
None
Integrity
None
Availability
Low
Scope
Unchanged
Exploitation
Is it being used?
Exploit prediction (EPSS)0.3% · higher than 23% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
ZE
zebra · ZcashFoundation
before 6.2.1 · source: vendor
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-104421
CVE.org
https://www.cve.org/CVERecord?id=CVE-2026-104421
vendor-advisory
https://github.com/ZcashFoundation/zebra/security/advisories/GHSA-x93j-mj2f-q338
third-party-advisory
https://www.vulncheck.com/advisories/zebra-before-6.2.1-block-download-denial-of-service-via-knownblock-senthashes-lockout
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