LibreSSL ocspcheck EUVD-2026-111550

Exploitation requires the victim to run ocspcheck to validate a certificate, AND the attacker to occupy one of two positions: (1) control of the OCSP responder specified in the certificate's AIA extension, or (2) an on-path/MITM position able to intercept and inject into plaintext HTTP OCSP (AIA) traffic - OCSP-over-HTTP is unencrypted, enabling the interception path. The attacker then streams unbounded HTTP response headers or body data into http_head_read()/http_body_read(), which (before the fix) buffered without a size limit. Limiting factors: impact is denial of service only (certificate status checks fail); the AT:P metric reflects the required responder-control or on-path precondition, so this is not a trigger-from-anywhere flaw against arbitrary Internet hosts; no authentication is required of the attacker, but the specific network position is.

Signals are mixed and point to moderate, conditional risk despite the 8.2 'High' headline. The only CVSS vector supplied is CVSS 4.0 (AV:N/AC:L/AT:P/PR:N/UI:N) and its impact is purely availability (VA:H; VC:N/VI:N/VA... C and I none) - this is a denial-of-service against certificate-status checking, not a compromise of confidentiality or integrity, and it affects the ocspcheck utility rather than LibreSSL's cryptographic library functions. Crucially, AT:P (attack requirements present) reflects that exploitation is not unconditional: the attacker must either control the OCSP responder named in a certificate's AIA or be on-path to intercept plaintext HTTP OCSP traffic. There is no EPSS score in the input, the CVE is NOT in CISA KEV, and no public exploit was identified, so exploitation is not demonstrated as widespread. The vendor/aggregator decision label is this_week (not act_now or emergency), consistent with a real-but-not-critical priority. Net: the 8.2 overstates practical urgency for typical deployments - this is a genuine availability bug worth patching on a normal cycle, not a high-CVSS issue masquerading as low risk, but also not an emergency. Note: no CVSS 3.1 vector was provided in the input, so 3.1 metrics below are independently assessed.

An attacker who operates the OCSP responder referenced in a target certificate's AIA field - or who can intercept the victim's plaintext HTTP OCSP request on-path - responds to ocspcheck with an endless stream of HTTP headers or body data. Because http_head_read() and http_body_read() buffered the response without any size cap, memory grows until the process is exhausted and the certificate status check fails. No public exploit code was identified, but the mechanism is confirmed by the fix, which adds a 64 KB header limit.