CVE-2026-104421: Incomplete Cleanup in ZcashFoundation zebra
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.
AI Analysis
Technical Summary
CVE-2026-104421 describes an incomplete cleanup vulnerability in ZcashFoundation's Zebra software prior to version 6.2.1. The flaw allows unauthenticated peers to disrupt block synchronization by sending a contextually invalid block that shares the header hash of an honest block. This causes the Request::KnownBlock mechanism to skip the honest block, leaving rejected hashes in SentHashes and preventing the node from downloading valid blocks, effectively blocking progress.
Potential Impact
The vulnerability can cause nodes running Zebra before 6.2.1 to fall behind the blockchain tip by blocking the download of valid blocks. This denial of service is possible without authentication and can degrade node synchronization and network reliability.
Mitigation Recommendations
Upgrade Zebra to version 6.2.1 or later where this incomplete cleanup vulnerability is fixed. No other mitigation or workaround is documented.
CVE-2026-104421: Incomplete Cleanup in ZcashFoundation zebra
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 v4.0
Score 6.9medium
Affected software
ZcashFoundation
zebra
pkg:github/zcashfoundation/zebraRun on your own infrastructure? Check whether these packages are installed with threat-finder — our free open-source scanner.
AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
CVE-2026-104421 describes an incomplete cleanup vulnerability in ZcashFoundation's Zebra software prior to version 6.2.1. The flaw allows unauthenticated peers to disrupt block synchronization by sending a contextually invalid block that shares the header hash of an honest block. This causes the Request::KnownBlock mechanism to skip the honest block, leaving rejected hashes in SentHashes and preventing the node from downloading valid blocks, effectively blocking progress.
Potential Impact
The vulnerability can cause nodes running Zebra before 6.2.1 to fall behind the blockchain tip by blocking the download of valid blocks. This denial of service is possible without authentication and can degrade node synchronization and network reliability.
Mitigation Recommendations
Upgrade Zebra to version 6.2.1 or later where this incomplete cleanup vulnerability is fixed. No other mitigation or workaround is documented.
Technical Details
- Data Version
- 5.2
- Assigner Short Name
- VulnCheck
- Date Reserved
- 2026-10-02T00:46:23.830Z
- Cvss Version
- 4.0
- State
- PUBLISHED
Threat ID: 6abf99afa43b0b3b89b26900
Added to database: 10/02/2026, 11:46:55 UTC
Last enriched: 10/02/2026, 12:16:52 UTC
Last updated: 10/02/2026, 22:17:34 UTC
Views: 5
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