CVE-2026-111943

A flaw was found in Go's crypto/x509 package. The certificate verification process fails to block trust in intermediate certificates associated with a compromised Certificate Authority (CA). A remote attacker presenting a certificate signed by these intermediate authorities can impersonate legitimate servers during secure connections. This flaw can enable an attacker to conduct a man-in-the-middle (MitM) attack to intercept or alter confidential communications.

This vulnerability is rated Important because Go applications validating TLS certificates could accept unauthorized certificates issued by distrusted intermediate Certificate Authorities, potentially compromising the integrity and confidentiality of secure network communications. Any Go-based client or server relying on standard certificate verification may be exposed to man-in-the-middle attacks if an attacker intercepts traffic using certificates derived from these intermediate keys. Exploitation requires specific network positioning and certificates generated by the untrusted intermediate authorities, limiting opportunistic widespread abuse.

The CVSS score(s) listed for this vulnerability do not reflect the associated product's status, and are included for informational purposes to better understand the severity of this vulnerability.

See the security bulletin for a detailed mitigation procedure.