OpenSSL QUIC: a peer withholding acknowledgements makes ACK-only metadata accumulate for the connection's life

Impact

OpenSSL stores transmit metadata for ACK-only packets even though the QUIC protocol never requires a peer to acknowledge them. A peer that completes a handshake, forces a stream of ACK-only responses by sending PING frames, and then withholds acknowledgements for ack-eliciting data causes that metadata to be retained for the lifetime of the connection. Growth is connection-scoped, so a single association is survivable; the risk is a client opening many concurrent QUIC connections and driving all of them the same way until the server exhausts memory. On a fleet the concern is a QUIC-fronted gateway or storage endpoint whose OOM kill lands on a shared node rather than on the abusive client.

Who can reach it

A remote peer that can complete a QUIC handshake with the OpenSSL endpoint. Protocol-level handshake completion is required, but no application-level credential; effect scales with the number of connections the attacker is allowed to open.

What to do

Upgrade to the fixed OpenSSL release named in the 2026-08-25 advisory and restart QUIC-serving processes. Only the OpenSSL QUIC stack is affected. Until then, per-source connection limits and idle timeouts on the QUIC listener bound how much memory one client can pin, and a memory cgroup limit on the service keeps an OOM from taking neighbours with it. The record does not name a fixed version for this CVE.

References

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