CVE-2026-104423 Zebra before 6.2.1 Denial of Service via Uncapped V6 Shielded Proof Verification
Unauthenticated attackers can cause Zebra nodes to stall block verification by flooding the verification queue with invalid zero-fee transactions.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- None listed
What is CVE-2026-104423?
CVE-2026-104423 is a high-severity denial of service vulnerability in ZcashFoundation zebra, published on 2 Oct 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
Zebra (zebrad) before 6.2.1 contains an asymmetric resource consumption vulnerability that allows unauthenticated peers to stall block verification by pushing V6 mempool transactions with invalid Halo2 proofs. Attackers can flood the shared unprioritized Halo2 verification queue with zero-fee transactions carrying zero-filled Orchard and Ironwood proofs, causing nodes to fall behind the chain tip.
Weakness: CWE-405
Which versions are affected by CVE-2026-104423?
How do I fix CVE-2026-104423?
No fix has been published for CVE-2026-104423 yet. Limit exposure of the affected software until one is available.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-104423 being exploited?
There is no known exploitation of CVE-2026-104423 in the wild and no public exploit code.
Sources
Also known as GHSA-2p4c-3q4q-p463, GHSA-4x5w-56x5-cmfr.