ZcashFoundation Zebra: Denial of service via malformed V6 transaction
Summary
Zebra, the Zcash full node software, versions 6.4.0 before 6.4.2 can be crashed by a single malformed version 6 transaction sent over the peer-to-peer network. The node parses the transaction under a pre-NU6.3 consensus branch ID, and a later size computation aborts the zebrad process. No authentication or completed handshake is required, and the attacker can repeat the crash after each restart. The impact is limited to availability; the vendor reports no effect on funds or consensus.
Affected
- ZcashFoundation Zebra (zebrad) 6.4.0 to before 6.4.2 (6.4.0 and 6.4.1)
Fixed in
- Upgrade to Zebra 6.4.2 (fixed in zebra-chain 13.0.1 as well)
Workaround
- Unknown. The vendor documents no mitigation other than upgrading.
Exploitation
- Exploited in the wild: Unknown; no evidence found in the sources checked.
- Public proof of concept: none found.
- CISA SSVC: exploitation none, automatable yes, technical impact partial.
- EPSS: 0.00432 (low).
Our recommendation
- Upgrade all Zebra nodes from 6.4.0 or 6.4.1 to 6.4.2 promptly, using only official ZcashFoundation releases or the official zfnd/zebra image.
- Verify that the node restarts cleanly after the upgrade and monitor for repeated crashes.
- Restrict exposure of the peer port where it is not required, and check whether the node is reachable from the internet.
- Relevance for typical SMEs is low; it applies mainly to businesses operating Zcash nodes.
Public exploits
PoC-in-GitHub, Metasploit and Exploit-DB list nothing for this CVE.
Research sources
- GitHub Security Advisory GHSA-h5rr-8pqv-grp9 github.com
- Fix commit 008abac github.com
- Zebra v6.4.2 release github.com
- VulnCheck advisory www.vulncheck.com
- OSV record CVE-2026-109363 osv.dev
- NVD record via Vulners vulners.com
Researched and written up in English and German by an AI (Claude by Anthropic) based on NVD, CISA, EPSS and the sources listed. The vendor information is authoritative. Researched on 1 Nov 2026, 04:46.
Original description (NVD)
ZcashFoundation Zebra 6.4.0 before 6.4.2 parses version 6 transactions carrying a pre-NU6.3 consensus branch ID, but the size computation during UnminedTx construction treats re-serialization of the Orchard bundle as infallible, so the resulting error trips an expect that aborts zebrad. Unauthenticated peers can send a single pre-handshake tx message to crash the node, and can repeat this after each restart.
Sources
The tracker combines official, freely usable data sources – updated continuously:
- NVD (NIST) – CVEs, rating (CVSS), affected products
- CISA KEV – vulnerabilities confirmed by CISA as actively exploited
- CISA Vulnrichment – CISA assessment (SSVC) in the official CVE record
- FIRST EPSS – probability of exploitation
- Microsoft MSRC – Patch Tuesday: vulnerabilities, severity, updates
- PoC-in-GitHub – public proof-of-concept repositories
- Metasploit (Rapid7) – modules of the Metasploit Framework
- Exploit-DB (OffSec) – archive of public exploits (links only)
- Patch days: official vendor pages (linked per vendor) (Vendor patch days)
This product uses data from the NVD API but is not endorsed or certified by the NVD. EPSS data © FIRST.org.
Affected? We can help.
We check whether your systems are affected, install updates and close the gap – continuously with the System Health Checker if you wish.