Incorrect Block Size Calculation in Zebra by Zcash Foundation
CVE-2026-104424

6.3MEDIUM

Key Information:

Vendor

Zcashfoundation

Status
Zebra
Vendor
CVE Published:
2 October 2026

What is CVE-2026-104424?

Zebra versions prior to 6.1.0 contain an incorrect calculation vulnerability in the ZIP-317 block template selector. This issue arises from a miscalculation that omits crucial header and transaction-count sizes when determining the block budget. Attackers can exploit this vulnerability by placing valid selectable transactions into a victim miner's mempool. This allows them to manipulate the block templates into oversized configurations, leading to block rejections and wasted proof-of-work resources. Users of Zebra are urged to upgrade to mitigate potential risks associated with this flaw.

Affected Version(s)

zebra 0 < 6.1.0

zebra 6.1.0

References

https://github.com/ZcashFoundation/zebra/security/advisor...
vendor-advisory
https://www.vulncheck.com/advisories/zebra-before-6.1.0-i...
third-party-advisory

CVSS V4

Score:
6.3
Severity:
MEDIUM
Confidentiality:
None
Integrity:
None
Availability:
Low
Attack Vector:
Network
Attack Complexity:
High
Attack Required:
Physical
Privileges Required:
Undefined
User Interaction:
None

Timeline

  • Vulnerability published

  • Vulnerability Reserved

Credit

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