CVE-2026-40880

# Conceptual PoC for CVE-2026-40880 # This script demonstrates the logic to create a transaction valid at H+1 but invalid at H+2 def craft_malicious_tx(current_height): """ Constructs a transaction that is valid at current_height + 1 but expires or becomes invalid at current_height + 2. """ tx = { "version": 4, "locktime": current_height + 1, # Valid at H+1, technically expired/invalid logic at H+2 depending on implementation "inputs": [], "outputs": [] } # In a real scenario, specific Zcash consensus rules (e.g., expiry height) are manipulated return tx # Step 1: Attacker observes current height H height_H = get_current_block_height() # Step 2: Create transaction valid for H+1 malicious_tx = craft_malicious_tx(height_H) # Step 3: Broadcast transaction to vulnerable Zebra node broadcast_transaction(malicious_tx) # Step 4: Mine block at H+2 including this transaction # The vulnerable node accepts it due to cache bypass logic mine_block_at_height(height_H + 2, [malicious_tx])

{"cve": {"id": "CVE-2026-40880", "sourceIdentifier": "[email protected]", "published": "2026-04-21T20:17:01.687", "lastModified": "2026-04-27T18:26:19.257", "vulnStatus": "Analyzed", "cveTags": [], "descriptions": [{"lang": "en", "value": "ZEBRA is a Zcash node written entirely in Rust. Prior to zebrad version 4.3.1 and zebra-consensus version 5.0.2, 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. This vulnerability is fixed in zebrad version 4.3.1 and zebra-consensus version 5.0.2."}], "metrics": {"cvssMetricV40": [{"source": "[email protected]", "type": "Secondary", "cvssData": {"version": "4.0", "vectorString": "CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:N/VC:N/VI:H/VA:H/SC:N/SI:H/SA:H/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X", "baseScore": 7.2, "baseSeverity": "HIGH", "attackVector": "NETWORK", "attackComplexity": "LOW", "attackRequirements": "PRESENT", "privilegesRequired": "LOW", "userInteraction": "NONE", "vulnConfidentialityImpact": "NONE", "vulnIntegrityImpact": "HIGH", "vulnAvailabilityImpact": "HIGH", "subConfidentialityImpact": "NONE", "subIntegrityImpact": "HIGH", "subAvailabilityImpact": "HIGH", "exploitMaturity": "NOT_DEFINED", "confidentialityRequirement": "NOT_DEFINED", "integrityRequirement": "NOT_DEFINED", "availabilityRequirement": "NOT_DEFINED", "modifiedAttackVector": "NOT_DEFINED", "modifiedAttackComplexity": "NOT_DEFINED", "modifiedAttackRequirements": "NOT_DEFINED", "modifiedPrivilegesRequired": "NOT_DEFINED", "modifiedUserInteraction": "NOT_DEFINED", "modifiedVulnConfidentialityImpact": "NOT_DEFINED", "modifiedVulnIntegrityImpact": "NOT_DEFINED", "modifiedVulnAvailabilityImpact": "NOT_DEFINED", "modifiedSubConfidentialityImpact": "NOT_DEFINED", "modifiedSubIntegrityImpact": "NOT_DEFINED", "modifiedSubAvailabilityImpact": "NOT_DEFINED", "Safety": "NOT_DEFINED", "Automatable": "NOT_DEFINED", "Recovery": "NOT_DEFINED", "valueDensity": "NOT_DEFINED", "vulnerabilityResponseEffort": "NOT_DEFINED", "providerUrgency": "NOT_DEFINED"}}], "cvssMetricV31": [{"source": "[email protected]", "type": "Primary", "cvssData": {"version": "3.1", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:H", "baseScore": 8.1, "baseSeverity": "HIGH", "attackVector": "NETWORK", "attackComplexity": "LOW", "privilegesRequired": "LOW", "userInteraction": "NONE", "scope": "UNCHANGED", "confidentialityImpact": "NONE", "integrityImpact": "HIGH", "availabilityImpact": "HIGH"}, "exploitabilityScore": 2.8, "impactScore": 5.2}]}, "weaknesses": [{"source": "[email protected]", "type": "Primary", "description": [{"lang": "en", "value": "CWE-1025"}]}], "configurations": [{"nodes": [{"operator": "OR", "negate": false, "cpeMatch": [{"vulnerable": true, "criteria": "cpe:2.3:a:zfnd:zebra-consensus:*:*:*:*:*:rust:*:*", "versionEndExcluding": "5.0.2", "matchCriteriaId": "EA4CC734-BCB2-4864-A7CC-B5D093489379"}, {"vulnerable": true, "criteria": "cpe:2.3:a:zfnd:zebrad:*:*:*:*:*:rust:*:*", "versionEndExcluding": "4.3.1", "matchCriteriaId": "0D5F3C05-ECFC-43B1-9168-8E114125F6B7"}]}]}], "references": [{"url": "https://github.com/ZcashFoundation/zebra/security/advisories/GHSA-xvj8-ph7x-65gf", "source": "[email protected]", "tags": ["Vendor Advisory"]}]}}