# CVE-2026-104423: Zebra asymmetric resource consumption in shielded proof verification

Source: https://junglewise.ai/threats/cve-2026-104423-zebra-zebrad-before-6-2-1-contains-an-asymmetric-resource  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-10-02. Updated: 2026-10-05  
License: CC BY 4.0 with a link back

CVE-2026-104423 · Severity: high · CVSS 7.5 · Published 2026-10-02

Zebra is a privacy-focused cryptocurrency node implementation that validates transactions on the Zcash network. An unauthenticated attacker can flood the transaction verification queue with crafted transactions bearing invalid cryptographic proofs, causing the node to stall and fall behind the blockchain tip, resulting in a denial of service. No funds are lost and the node recovers once the attack stops.

Technologies: [Zcash Foundation Zebra](https://junglewise.ai/threats/technologies/zebra). Vendors: [Zcash Foundation](https://junglewise.ai/threats/vendors/zcash-foundation).

## Quick answers

**Is CVE-2026-104423 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-104423 being exploited in the wild.

**How severe is CVE-2026-104423?** High severity, with a CVSS score of 7.5, published 2 October 2026.

**Which products and versions are affected?** Zcash Foundation Zebra before 6.2.1.

**Is there a fix for CVE-2026-104423?** Yes: fixed in Zebra 6.2.1 and later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-104423 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-104423?** Check whether you run Zcash Foundation Zebra at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- Fixed in Zebra 6.2.1 and later

## Technical details

The vulnerability is an asymmetric resource consumption issue in the Halo2 proof verification pipeline. Zebra caps concurrent mempool transaction verification by transaction count (5 per peer, 500 global) but not by verification cost. Since Ironwood (NU6.3) allows a single V6 transaction to carry two Halo2 proofs (Orchard and Ironwood bundles) without raising the cap, an attacker can queue expensive-to-verify but cheap-to-produce transactions with canonically-sized invalid proofs. The shared unprioritized verification queue between mempool and block transactions causes block verification to stall behind the attacker's queue.

## Affected products

- Zcash Foundation Zebra before 6.2.1

## Timeline

- 2026-08-17: disclosed: GitHub Security Advisory published
- 2026-10-02: advisory: Public advisory released

## References

- [https://github.com/ZcashFoundation/zebra/security/advisories/GHSA-2p4c-3q4q-p463](https://github.com/ZcashFoundation/zebra/security/advisories/GHSA-2p4c-3q4q-p463)
- [https://www.vulncheck.com/advisories/zebra-before-6.2.1-denial-of-service-via-uncapped-v6-shielded-proof-verification](https://www.vulncheck.com/advisories/zebra-before-6.2.1-denial-of-service-via-uncapped-v6-shielded-proof-verification)

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