Hex EUVD-2026-97497

Exploitation requires three concurrent conditions: (1) the attacker holds a man-in-the-middle position able to intercept the victim's HTTPS connection to a Hex host; (2) the attacker possesses a valid certificate for that Hex host issued by a CA that exists in Hex's bundled CA store; and (3) the victim has set cacerts_path (HEX_CACERTS_PATH) to a custom CA store that deliberately omits that bundled CA. The flaw is that Hex.HTTP.SSL.ssl_opts/1 builds the partial_chain callback from the bundled store regardless of cacerts_path, so a chain reaching any bundled CA is accepted even when the configured store excludes it. Limiting factors that reduce real-world risk: the custom cacerts_path setting is non-default and uncommon; a privileged network/MITM position is required; the attacker must obtain a certificate for the exact target host from an in-bundle CA; and hostname verification still applies, so the certificate must match the impersonated host's name.

This is a medium-severity (CVSS 4.0 base 5.9) improper certificate validation flaw (CWE-295) whose real-world risk is substantially constrained by its preconditions rather than its impact. The provided CVSS 4.0 vector (AV:N/AC:H/AT:P/PR:N/UI:A/VC:H/VI:L) encodes exactly why: although the attack is network-reachable and requires no privileges on the target, it carries High attack complexity, a Present attack requirement (AT:P), and active user interaction/condition (UI:A) - all signalling that exploitation is not opportunistic. The attacker must simultaneously (1) hold a man-in-the-middle position on the HTTPS connection, (2) possess a valid certificate for a Hex host issued by a CA that is in Hex's bundled store, and (3) rely on the victim having configured a custom cacerts_path/HEX_CACERTS_PATH store that omits that CA - a non-default, relatively uncommon hardening configuration. No EPSS score was supplied in the input, so exploitation probability cannot be quantified; there is no CISA KEV listing and no public exploit code referenced, so there is no evidence of active exploitation. No SSVC decision data was provided. The signals are internally consistent (no contradictions between vector and description), and collectively point to a targeted, narrow-impact issue rather than a widespread or urgent threat. The confidentiality impact is genuine (host impersonation on a trusted TLS channel), but the conjunction of MITM capability, a specifically-issued certificate, and a particular misconfiguration keeps real-world priority low-to-moderate; patch promptly where cacerts_path is used, but this is not a drop-everything issue.

A user hardens Hex by setting HEX_CACERTS_PATH to a trimmed CA store intended to exclude a particular public CA, expecting Hex to reject hosts whose chains lead to that CA. An attacker positioned to intercept the victim's HTTPS traffic (e.g. on a compromised network or via upstream routing control) presents a certificate for the Hex host that chains to a CA still present in Hex's bundled store; because the partial_chain callback is always built from the bundled store, validation succeeds and the attacker impersonates the host to serve malicious or tampered package data. No public exploit code was identified at time of analysis.