Bug 2549700 (CVE-2026-103503)

Summary: CVE-2026-103503 hex: hex: Host impersonation via improper CA certificate store validation
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
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Version: unspecifiedKeywords: Security
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OS: Linux   
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A flaw was found in hex. When a custom Certificate Authority (CA) store is configured to restrict trusted authorities, hex inadvertently continues to validate certificate chains against its bundled CA certificates. An attacker capable of intercepting network traffic and holding a certificate issued by a bundled CA can impersonate a trusted host to the client. This issue can result in unauthorized data disclosure or tampering.
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Description OSIDB Bzimport 2026-10-12 15:33:14 UTC 
Improper Certificate Validation vulnerability in hexpm hex allows an attacker who can intercept HTTPS connections, and holds a certificate for a Hex host issued by a CA in Hex's bundled CA store, to impersonate that host to users who set cacerts_path to a CA store that leaves that CA out.

cacerts_path (HEX_CACERTS_PATH) is documented as the path to the CA certificate store, used instead of the CA bundle that ships with Hex. Hex.HTTP.SSL.ssl_opts/1 passes the configured store as the cacerts option, but builds the partial_chain callback from the bundled store whether cacerts_path is set or not. Hex.HTTP.SSL.partial_chain/2 accepts a server chain when any certificate in it has the same public key as a bundled CA certificate, so a chain that leads to a bundled CA passes verification although the configured store doesn't contain that CA. Hostname verification still applies.

This issue affects hex: from 0.20.2 before 2.5.2.