CVE-2026-52736: ZcashFoundation Zebra block suppression via same-header body poisoning

CVE-2026-52736 · Severity: high · CVSS 4 · Published 2026-08-18

Zebra, a Zcash node implementation, is vulnerable to a denial-of-service attack that can permanently stall a node at a specific block height. By exploiting how the software handles block validation, a remote attacker can trick a node into rejecting legitimate new blocks, causing it to fall behind the rest of the network. This affects the reliability of services relying on the node, such as wallets, block explorers, and mining infrastructure.

Technologies: zebra-state (crates.io), zebrad (crates.io). Vendors: crates.io.

Quick answers

Is CVE-2026-52736 exploited in the wild?
No. Junglewise Threat Intelligence has no report of CVE-2026-52736 being exploited in the wild.
How severe is CVE-2026-52736?
High severity, with a CVSS score of 4, published 18 August 2026.
Which products and versions are affected?
zebra-state (crates.io) <= 6.0.0, SEMVER:introduced=0,fixed=7.0.0; zebrad (crates.io) <= 4.4.1, SEMVER:introduced=0,fixed=4.5.0.
Is there a fix for CVE-2026-52736?
Yes. zebra-state (crates.io): upgrade to 7.0.0 or later; zebrad (crates.io): upgrade to 4.5.0 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2026-52736 attacked?
It is attacked over the network, in a software library.
Am I affected by CVE-2026-52736?
Check whether you run zebra-state (crates.io) or zebrad (crates.io) 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

  • zebra-state (crates.io): upgrade to 7.0.0 or later
    cargo update -p zebra-state
  • zebrad (crates.io): upgrade to 4.5.0 or later
    cargo update -p zebrad

Technical details

A vulnerability in Zebra's block processing logic allows for block suppression through a 'same-header body poisoning' attack. Zebra records a block hash in its internal cache before contextual validation is complete; if validation fails, the hash is not removed. An attacker can exploit ZIP-244 transaction malleability to construct a poisoned block body that shares the same header hash as a valid block. By winning a propagation race and delivering the poisoned body first, the attacker causes Zebra to cache the hash and reject the subsequent valid block as a duplicate. This stalls the node at the current height. The issue is fixed in Zebra 4.4.2 and zebra-state 7.0.0 by ensuring stale entries are removed from the cache upon validation failure.

Affected products

  • ZcashFoundation zebrad <= 4.4.1
  • ZcashFoundation zebra-state <= 6.0.0

Identifiers

  • CVE-2026-52736
  • GHSA-4m69-67m6-prqp

Timeline

  • 2026-05-29: disclosed: Reported to ZcashFoundation
  • 2026-07-02: advisory: GitHub Advisory published

References

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