CVE-2026-103503

5.9Medium

Published 12 Oct 2026 · NVD status: Deferred · AI triage by gemini-3.8-flash

5.9Medium

Attack vector: Network
Complexity: High
Privileges needed: None
User interaction: Active
Impact: High impact on confidentiality
Weakness: CWE-295

Impact

A machine-in-the-middle attacker holding a valid certificate from Hex's bundled CAs can impersonate a Hex host even if you explicitly excluded that CA via a custom CA store. The attacker requires network interception capabilities and a certificate matching the target host.

Root cause

Hex always builds its partial_chain validation callback using the bundled CA bundle, causing it to trust bundled CA certificates even when overridden with cacerts_path.

Affected systems

hex from 0.20.2 before 2.5.2

CVSS v4.0 · CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:A/VC:H/VI:L/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

Fix & remediation

Upgrade hex to version 2.5.2 or later. No interim mitigation is documented if you rely on cacerts_path to restrict CAs, so prioritize the upgrade.

shell

$ mix local.hex --force

AI-suggested. Run it in staging first and check it against the vendor advisory. Why?

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NVD description

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.

References

Source: nvd.nist.gov/vuln/detail/CVE-2026-103503