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0xCERT Security Advisory 0xCERT-2026-0226
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Advisory-ID:  0xCERT-2026-0226
Severity:     High
Published:    2026-04-18T00:41:54.000Z
Updated:      2026-10-08T22:48:28.412Z
Chains:       n/a
URL:          https://www.0xcert.com/advisory/0xCERT-2026-0226

Title: Zebra: Cached Mempool Verification Bypasses Consensus Rules for Ahead-of-Tip Blocks

Summary
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Zebra: Cached Mempool Verification Bypasses Consensus Rules for Ahead-of-Tip Blocks. A logic error in Zebra's transaction verification cache could allow a malicious miner to induce a consensus split. By carefully submitting a transaction that is valid for height H+1 but invalid for H+2 and then mining that transaction in a block at height H+2, a miner could cause vulnerable Zebra nodes to accept an invalid block, leading to a consensus split from the rest of the Zcash network.

Details
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Summary
A logic error in Zebra's transaction verification cache could allow a malicious miner to induce a consensus split. By carefully submitting a transaction that is valid for height H+1 but invalid for H+2 and then mining that transaction in a block at height H+2, a miner could cause vulnerable Zebra nodes to accept an invalid block, leading to a consensus split from the rest of the Zcash network.

Affected
- - zebra-consensus (rust) < 5.0.2 — fixed in 5.0.2
- - zebrad (rust) < 4.3.1 — fixed in 4.3.1

Severity
High (CVSS 7.2), as rated by the upstream advisory.

Recommended actions
- - Upgrade zebra-consensus to 5.0.2 or later
- - Upgrade zebrad to 4.3.1 or later

Source & attribution
This 0xCERT advisory summarises GHSA-xvj8-ph7x-65gf / CVE-2026-40880 from the GitHub Advisory Database, credited upstream to sangsoo-osec, conradoplg, mpguerra: https://github.com/advisories/GHSA-xvj8-ph7x-65gf. Details may change; refer to the original source for the authoritative record.

References
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- - https://github.com/advisories/GHSA-xvj8-ph7x-65gf
- - CVE-2026-40880
- - https://github.com/ZcashFoundation/zebra/security/advisories/GHSA-xvj8-ph7x-65gf
- - https://nvd.nist.gov/vuln/detail/CVE-2026-40880

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