The vulnerability lies in Zebra’s handling of version 6 transactions that include an older consensus branch ID. During the construction of an unmined transaction, the code assumes that re-serialization of the Orchard bundle will never fail. When it does fail, an internal expect aborts the zebra daemon. This failure causes the node to terminate, resulting in a denial of service.

ZcashFoundation Zebra versions prior to 6.4.2, specifically those in the 6.4.0 series, are affected. The vulnerability is referenced by the Zcash Foundation’s advisories and affects all deployments running these zebra binaries.

Unauthenticated peers can trigger the crash by sending a single malformed pre‑handshake transaction, and they can repeat the attack after each node restart. The CVSS score of 8.7 indicates high severity. EPSS data is not available, and the vulnerability is not listed in CISA’s KEV catalog, but the absence of exploit data does not reduce the risk of an attacker exploiting the remote denial-of-service flaw using the described technique.