LibreSSL ocspcheck EUVD-2026-111549

Exploitation requires a precise combination: (1) a host actually using LibreSSL's ocspcheck utility (not merely linking libtls/libssl), (2) an OCSP responder URL that uses the https scheme but a TCP port other than 443 - this is the trigger, because url2host() discards the scheme and http_alloc() only enables TLS when port==443, so such requests go out as cleartext HTTP, and (3) an attacker with an on-path (man-in-the-middle/passive-tap) network position to read the traffic. Limiting factors: the https-on-non-443-port OCSP configuration is non-default and uncommon, the attacker cannot inject or modify (read-only metadata exposure), and only OCSP request fields (serial numbers, issuer hashes, nonces) leak - no credentials or key material. These constraints are reflected in the supplied AC:H and AT:P metrics.

This is a genuine but low-urgency information-disclosure issue, and the signals are internally consistent rather than conflicting. The supplied CVSS 4.0 vector (AV:N/AC:H/AT:P/PR:N/UI:N/VC:L/VI:N/VA:N) scores 6.3 (medium) and correctly reflects a flaw that is network-reachable but gated by both high attack complexity (AC:H) and a specific attack requirement (AT:P): the attacker must occupy an on-path position AND the victim's ocspcheck invocation must target an https OCSP responder URL on a non-443 port - the exact condition under which url2host() discards the scheme and http_alloc() fails to select TLS. Confidentiality impact is low (VC:L) and there is no integrity or availability impact (VI:N/VA:N), because only OCSP request metadata - certificate serial numbers, issuer name hashes, and nonces - leaks, not private keys or credentials. No EPSS score was supplied, so widespread-exploitation probability cannot be quantified from the input. KEV status is not listed (treat as not present): there is no confirmed active exploitation. The vuln.today decision label is 'this_month', which aligns with a patch-available, medium-severity, narrowly-conditioned bug rather than an emergency. Net: real and worth patching on a routine cycle, but the narrow trigger conditions and on-path requirement keep real-world risk well below the raw CVSS number's first impression.

An attacker already positioned on the network path (e.g., a malicious Wi-Fi gateway, compromised router, or ISP-level interceptor) waits for a host running LibreSSL ocspcheck to validate a certificate whose OCSP responder URL uses the https scheme on a non-443 port. Because ocspcheck sends the request in cleartext over plain HTTP in that case, the attacker passively reads the OCSP request and harvests the certificate serial number, issuer name hash, and nonce. No public exploit was identified at time of analysis, and the high attack complexity plus required on-path position make this an opportunistic metadata-disclosure rather than a reliable remote compromise.