OpenSSL CVE-2026-63075

The target must be running OpenSSL 3.4.0-3.4.6, 3.5.0-3.5.7, 3.6.0-3.6.3, or 4.0.0-4.0.1 with the QUIC stack actively in use - TLS-only deployments are not affected. The attacker must be able to reach the QUIC UDP port and successfully complete a QUIC handshake, meaning the endpoint must be network-accessible without connection-level authentication barriers prior to handshake completion. Post-handshake, no credentials or elevated session state are required. Impact scales with attack duration and concurrency: a single short-lived connection produces negligible memory growth, while sustained connections or high-concurrency scenarios are required to reach service-affecting exhaustion. Exploitation is limited to: (1) QUIC-enabled OpenSSL versions in the affected range, (2) UDP endpoints reachable by the attacker, and (3) sufficient connection persistence to accumulate meaningful memory pressure.

The CVSS 7.5 High vector (AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H) accurately characterizes a network-reachable, zero-authentication DoS with no confidentiality or integrity impact; these metrics align with the description's post-handshake trigger requiring no special privileges. SSVC rates the attack as automatable with partial technical impact and no current exploitation, which is internally consistent - the absence of KEV listing and POC confirms this is not yet weaponized but is mechanically straightforward to script. EPSS data is not available in the provided input and cannot be cited. Practical risk is significantly gated by QUIC adoption: OpenSSL's QUIC stack was introduced in 3.2 and real-world QUIC server deployments using OpenSSL (versus alternatives like quiche or msquic) are still maturing, reducing population-level blast radius compared to a TLS vulnerability. However, affected QUIC endpoints are directly exposed to exploitation without any user interaction or elevated privileges, and sustained or concurrent connections accelerate memory exhaustion, making this a genuine operational risk for environments actively serving QUIC traffic.

An attacker directs a script to open many concurrent QUIC connections to an OpenSSL-based server (e.g., a reverse proxy or application server with QUIC enabled), completing the handshake on each, then continuously transmitting PING frames to force ACK-only responses while deliberately withholding its own acknowledgments. Over time, each connection accumulates unreleased ACK-only packet metadata in the server's QUIC ACK manager, progressively consuming heap memory until the server process is terminated by the OS OOM killer or becomes unresponsive. No public exploit code exists at time of analysis, but the attack mechanism is mechanically straightforward to implement from the public description.