CVE-2026-53970 describes a missing integrity verification vulnerability in the Ruby compatibility shim of ZeroBrew version 0.3.1 and prior. The flaw allows an attacker who can intercept network traffic to replace or modify downloads for secondary resources or URL-based patches referenced in shim.rb. Because there is no checksum validation, malicious content injected by the attacker can execute arbitrary code during source builds initiated by the 'zb install --build-from-source' command. This vulnerability arises from the lack of integrity checks on downloaded components, enabling code execution without user warning.

An attacker capable of intercepting or modifying network traffic can inject malicious build steps or source modifications that execute during source builds. This leads to arbitrary code execution on the victim system without any integrity warning, potentially compromising the system running ZeroBrew. The CVSS 4.0 score of 7.5 (high severity) reflects the network attack vector, required user interaction, and high impact on confidentiality, integrity, and availability.

Patch status is not yet confirmed — check the vendor advisory for current remediation guidance. Until a fix is available, users should avoid using 'zb install --build-from-source' with untrusted sources or in untrusted network environments. Employing network-level protections such as TLS or VPNs to prevent interception may reduce risk.