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 Hexs 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 doesnt contain that CA. Hostname verification still applies.
This issue affects hex: from 0.20.2 before 2.5.2.
Weakness
The product does not validate, or incorrectly validates, a certificate.
Potential Mitigations
Related Attack Patterns
References
- https://cna.erlef.org/cves/CVE-2026-103503.html
- https://github.com/hexpm/hex/commit/5f5a2136c7cf5991b6e8a30d645ca9f8e74b0785
- https://github.com/hexpm/hex/commit/6232a6498015e559743bec4f4fbec9138837cec8
- https://github.com/hexpm/hex/commit/c9b26a46928bfcd546773571e09c1d05f4cd9fb7
- https://github.com/hexpm/hex/security/advisories/GHSA-rw8q-hg7m-cxgr
- https://osv.dev/vulnerability/EEF-CVE-2026-103503