CVE-2026-103503

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.

CVSS 4.0

5.9CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:A/VC:H/VI:L/VA:N/SC:N/SI:N/SA:N

EPSS

0.2% chance of exploitation in the next 30 days; higher than 10% of CVEs (scores of 2026-10-25)

CWE

CWE-295

Published

2026-10-12

Modified

2026-10-16

Record from

the NVD, synced 2026-10-19

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

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