CVE-2026-104420: Zebra before 6.3.0 Peer Misbehavior Ban Bypass via Gossiped Blocks

Severity: medium (CVSS 5.3 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-704

Description

Zebra before 6.3.0 contains a protection mechanism failure that allows unauthenticated peers to evade misbehavior scoring by supplying invalid gossiped blocks. The inbound cleanup step wrongly downcasts RouterError to VerifyBlockError and discards the score, so attackers can repeatedly force block download and Equihash verification without being banned.

Affected products

ZcashFoundation zebra: before 6.3.0 — fixed in 6.3.0

How to fix

Upgrade to a fixed version: ZcashFoundation zebra 6.3.0. Check the vendor advisory for mitigations.

References

https://github.com/ZcashFoundation/zebra/security/advisories/GHSA-8hh2-hrf2-cqf4
https://www.vulncheck.com/advisories/zebra-before-6.3.0-peer-misbehavior-ban-bypass-via-gossiped-blocks

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