CVE-2026-56864 in Google
Summary
by MITRE • 08/14/2026
A malicious GOSUMDB was capable of serving arbitrary module content not contained within the transparency log. This attack allows for a coordinating GOPROXY and GOSUMDB to serve a client malicious module content that cannot be detected by evaluating the transparency log. In order to determine if you have been affected: rm -r go.sum go.work.sum vendor/ && go mod tidy
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Analysis
by VulDB Data Team • 08/14/2026
The vulnerability involves a critical security flaw in the go module system that undermines the integrity verification mechanisms designed to protect against malicious package content. This issue stems from the interaction between goproxy and gosumdb services where an attacker can coordinate these components to deliver unauthorized module content that bypasses the transparency log validation process. The attack exploits the trust model inherent in go modules by allowing malicious actors to inject arbitrary code into dependency chains without detection, effectively compromising the entire supply chain security posture.
The technical flaw resides in the fundamental architecture of go's module verification system where gosumdb serves as a transparency log for verifying module integrity but can be subverted through malicious proxy coordination. When a client fetches modules through a compromised goproxy, it can receive content that is then validated against a manipulated gosumdb which fails to detect the malicious substitution because the verification process does not adequately cross-check the actual content against the expected checksums stored in the transparency log. This creates a dangerous gap where attackers can serve modified packages that pass all integrity checks while appearing legitimate within the system.
The operational impact of this vulnerability is severe as it allows for undetectable supply chain attacks that can compromise entire applications and systems. The attack vector enables malicious actors to inject backdoors, trojan horses, or other harmful code into dependency chains that would otherwise be considered trustworthy due to the golang module verification system. Organizations using go modules are at risk of having their applications compromised through seemingly legitimate dependencies, potentially leading to data breaches, system compromise, or unauthorized access to sensitive information.
Mitigation strategies must include immediate removal of existing module caches and reinitialization of the dependency management system through the recommended command sequence that clears all cached content and forces a complete rebuild of the module graph. System administrators should implement additional verification measures such as manual checksum validation, code review of critical dependencies, and monitoring for unusual network activity. Organizations should also consider implementing network-level controls to restrict access to known good goproxy endpoints and establish more robust verification processes that go beyond the basic transparency log checks. The vulnerability highlights the importance of defense in depth strategies and continuous monitoring for supply chain security breaches. This attack pattern aligns with common tactics used in software supply chain attacks and represents a significant concern for organizations relying on automated dependency management systems.