CVE-2026-104424: Zebra before 6.1.0 Incorrect Block Size Calculation in getblocktemplate

Severity: low (CVSS 3.7 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.3% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-10-02 · updated 2026-10-06
Weakness: CWE-131

Description

Zebra before 6.1.0 contains an incorrect calculation vulnerability in its ZIP-317 block template selector that omits header and transaction-count size from the block budget. Attackers can place valid selectable transactions in a victim miner's mempool to shape templates into oversized blocks, causing rejection and wasted proof-of-work.

Affected products

ZcashFoundation zebra: before 6.1.0 — fixed in 6.1.0

How to fix

Upgrade to a fixed version: ZcashFoundation zebra 6.1.0. Check the vendor advisory for mitigations.

References

https://github.com/ZcashFoundation/zebra/security/advisories/GHSA-95m2-vx53-v2jw
https://www.vulncheck.com/advisories/zebra-before-6.1.0-incorrect-block-size-calculation-in-getblocktemplate

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