# CVE-2026-40880: zebra-consensus — Fixed in 5.0.2 🦀 crates.io Not in CISA KEV # CVE-2026-40880 — zebra-consensus CVE-2026-40880 is a CWE-1025 vulnerability in zebra-consensus. A fix is available for zebra-consensus — see the affected versions and patch details below. Zebra: Cached Mempool Verification Bypasses Consensus Rules for Ahead-of-Tip Blocks Also known as[GHSA-xvj8-ph7x-65gf](/vulnerability/GHSA-xvj8-ph7x-65gf) Published Apr 21, 2026 Updated Oct 28, 2026 Affected 2 pkgs Patched 2 / 2 Exploits None indexed Exploitation data as of Nov 7, 2026 · OSV.dev, NVD, FIRST.org (EPSS) ## Exploitation Status ### No confirmed exploitation observed yet - CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment. Exploitation and automatability from CISA’s SSVC triage for CVE-2026-40880. ## EPSS Exploitation Probability [via FIRST.org ↗](https://www.first.org/epss/) 0.3%probability of exploitation in next 30 days Lower Risk0.00% Lower risk than most CVEs18th percentile — riskier than 18% of all scored CVEsHighest risk 0.00%0.31%0.63%0.94%0.0%0.3%May 26Sep 26Nov 26 Probability of exploitation in the next 30 days, from [FIRST.org EPSS](https://www.first.org/epss/). ## Real-World Exposure 2 pkgs affected 🦀`zebra-consensus`🦀`zebrad` Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects crates.io packages — download data is not available via public APIs for these ecosystems. ## Description ## CVE-2026-40880: Cached Mempool Verification Bypasses Consensus Rules for Ahead-of-Tip Blocks ### 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. ### Severity High - This is a Consensus Vulnerability that could allow a malicious miner to induce network partitioning, service disruption, and potential double-spend attacks against affected nodes. ### Affected Versions All Zebra versions prior to version 4.3.1. (Some older versions are not affected but are no longer supported by the network) ### Description The vulnerability exists due to a performance optimization whose goal is to improve performance of transaction validation if the transaction was previously accepted into the mempool (and thus was verified as valid). That however did not take into account that a transaction can be valid for a specific height, but invalid at higher heights; for example, it can contain an expiry height, a lock time, and it is always bound to a network upgrade, all of which are height-dependant. An attacker (specifically a malicious miner) could exploit this by (e.g. in the expiry height case): - Submitting a transaction with expiry height `H+1` (where `H` is the height of the current tip) - Mining a block `H+1`, and a block `H+2` that contains that same transaction, and submitting block `H+2` before `H+1` - Zebra nodes would accept `H+2` as valid (pending contextual verification) and wait for block `H+1`; when it arrives, Zebra would commit both blocks even if `H+2` contains an expired transaction - Other nodes (like `zcashd` or `zebrad` nodes without that transaction in their mempool) reject the block, resulting in a chain fork where the poisoned Zebra node is isolated. ### Impact **Consensus Failure** **Attack Vector**: Network (specifically via a malicious miner). **Effect**: Network partition/consensus split. **Scope**: Any Zebra node utilizing the transaction verification cache optimization for V5 transactions. ### Fixed Versions This issue is fixed in **Zebra 4.3.1**. We removed the performance optimization altogether, since we deemed it too risky. The fix ensures that verification is only skipped if the transaction's full integrity—including authorization data—is validated against the mempool entry. ### Mitigation Users should upgrade to Zebra 4.3.0 or later immediately. There are no known workarounds for this issue. Immediate upgrade is the only way to ensure the node remains on the correct consensus path and is protected against malicious chain forks. ### Credits Thanks to @sangsoo-osec for a thorough advisory submission that noticed the lock time issue, and to @shieldedonly with an also thorough advisory (that was submitted while we were working on the first one) who noticed that the issue applied to other aspects of the transaction validation. ## Affected Packages 2 total 2 fixed Ecosystem Package Vulnerable range Fix 🦀crates.io `zebra-consensus` all versions 5.0.2`cargo update -p zebra-consensus --precise 5.0.2` 🦀crates.io `zebrad` all versions 4.3.1`cargo update -p zebrad --precise 4.3.1` ## Affected Products 2 products · 2 configurations Application `zebra-consensus`zfnd < 5.0.2 range Application `zebrad`zfnd < 4.3.1 range ## Detection & mitigation playbook Open-source dependency 1. ### Detect Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for zebra-consensus, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version. 2. ### Fix Update zebra-consensus to 5.0.2 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-40880 is resolved across your whole dependency graph. 3. ### Workarounds If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands. ## Frequently Asked Questions \# CVE-2026-40880: Cached Mempool Verification Bypasses Consensus Rules for Ahead-of-Tip Blocks ## 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. ## Severity High - This is a Consensus Vulnerability that could allow a malicious miner O3 Security · Impact-Aware SCA ### Is CVE-2026-40880 in your dependencies? Find it across crates.io, including transitive dependencies. [Scan my dependencies](/book-demo) [How O3 SCA works](/impact-aware-sca)