# CVE-2026-123559: Zebra denial of service via quadratic sighash computation

Source: https://junglewise.ai/threats/cve-2026-123559-zebra-before-7-0-0-contains-an-inefficient-algorithmic  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-11-08. Updated: 2026-11-08  
License: CC BY 4.0 with a link back

CVE-2026-123559 · Severity: high · CVSS 7.5 · Published 2026-11-08

Zebra is a blockchain node implementation for the Zcash cryptocurrency that verifies transactions and blocks. An attacker can send specially crafted transactions with thousands of inputs that force a node to perform excessive computational work, stalling block verification for up to 14 minutes and disrupting the node's ability to validate legitimate transactions.

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

## Quick answers

**Is CVE-2026-123559 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-123559 being exploited in the wild.

**How severe is CVE-2026-123559?** High severity, with a CVSS score of 7.5, published 8 November 2026.

**Which products and versions are affected?** Zcash Foundation Zebra before 7.0.0.

**Is there a fix for CVE-2026-123559?** Yes: fixed in 7.0.0. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-123559 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-123559?** 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 7.0.0

## Technical details

The vulnerability is an inefficient algorithmic complexity issue in ZIP-244 and ZIP-243 transparent signature hash computation. Zebra recomputes digest hashes O(N) times for a transaction with N inputs, creating O(N²) total work; a single malformed transaction forces quadratic hashing that blocks the Rayon thread pool used for block verification. An unauthenticated remote peer can relay such transactions repeatedly without spending funds or incurring penalties, since failed scripts are not properly scored for misbehavior.

## Affected products

- Zcash Foundation Zebra before 7.0.0

## Timeline

- 2026-10-22: disclosed
- 2026-11-08: advisory

## References

- [https://github.com/ZcashFoundation/zebra/security/advisories/GHSA-j4cw-58mj-7w6v](https://github.com/ZcashFoundation/zebra/security/advisories/GHSA-j4cw-58mj-7w6v)
- [https://www.vulncheck.com/advisories/zebra-before-7.0.0-denial-of-service-via-quadratic-sighash-computation](https://www.vulncheck.com/advisories/zebra-before-7.0.0-denial-of-service-via-quadratic-sighash-computation)

## Related threats

- [Zebra incomplete cleanup in checkpoint sync stalls initial sync](https://junglewise.ai/threats/cve-2026-123560-zebra-before-7-0-0-contains-an-incomplete-cleanup-vulnerability)
- [Zcash Foundation Zebra zebrad reachable assertion denial of service](https://junglewise.ai/threats/cve-2026-123557-zcashfoundation-zebra-zebrad-before-7-0-0-contains-a-reachable)
- [Zcash Foundation Zebra protection mechanism failure in mempool lock-time scoring](https://junglewise.ai/threats/cve-2026-123556-zcashfoundation-zebra-from-4-5-0-before-7-0-0-contains-a)
- [Zebra misbehavior scoring bypass via invalid script verification](https://junglewise.ai/threats/cve-2026-123555-zebra-from-2-3-0-before-7-0-0-contains-a-denial-of-service)
- [Zebra peer ban bypass via exact IP keying](https://junglewise.ai/threats/cve-2026-109364-zebra-2-3-0-before-6-4-0-contains-a-protection-mechanism-failure)