Always-Incorrect Control Flow Implementation in Zcash - #VU137469
Published: July 14, 2026
Vulnerability identifier: #VU137469
CSH Severity: Medium
CVSS v4: 8.2 [CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N]
CVE-ID: N/A
CWE-ID: CWE-670
Exploitation vector: Remote access
Exploit availability:
No public exploit available
Vulnerability details
The vulnerability allows a remote attacker to cause a denial of service.
The vulnerability exists due to improper validity status handling in AcceptBlock() and CheckBlock() when processing a mutated NU5 block body that exceeds MAX_BLOCK_SIGOPS before auth commitment validation runs. A remote attacker can send a specially crafted block body to cause a denial of service.
The issue affects NU5-active networks and requires the poisoned block body to be delivered before the genuine body for the same header.
Affected software
Zcash
Remediation
Install security update from vendor's website.
Zcash - update to 6.20.0