OpenSSL QUIC ACK-only Packet Memory Leak Leading to DoS
CVE-2026-63075 Published on August 25, 2026

QUIC ACK-only Packet Retention Can Cause Memory Exhaustion
Issue summary: When OpenSSL processes QUIC traffic from a peer that repeatedly sends ack-eliciting packets while not acknowledging ACK-only responses, the QUIC stack can retain ACK-only packet metadata for the lifetime of the connection. Impact summary: A remote peer that can complete a QUIC handshake can cause connection-scoped memory growth which may lead to Denial of Service through memory exhaustion, especially with sustained traffic or many concurrent QUIC connections. CWE: CWE-770: Allocation of Resources Without Limits or Throttling Description: When the OpenSSL QUIC stack sends an ACK-only packet, there is no requirement by the QUIC protocol that the peer will acknowledge that ACK-only packet (i.e. it is itself not ack-eliciting). However, the OpenSSL implementation stores the metadata about the ACK frames regardless. In and of itself that's ok, but if a malicious peer establishes a connection, and then drives the connection such that ACK-only packets are forced from the OpenSSL implementation peer (i.e., by sending numerous PING frames), and then withholding any subsequent acks for ack-eliciting data, like legitimate data, said malicious peer can force inappropriate memory growth on the OpenSSL peer, potentially leading to a Denial of Service. The fix is to ensure that we account for the transmission of the ACK-only packet in the packet histories high and low watermark without actually storing the ACK-only packet metadata itself. FIPS impact: no The OpenSSL FIPS module is not affected as the QUIC code is outside the FIPS module boundary.

Vendor Advisory NVD

Vulnerability Analysis

CVE-2026-63075 can be exploited with network access, and does not require authorization privileges or user interaction. This vulnerability is considered to have a low attack complexity. The potential impact of an exploit of this vulnerability is considered to have no impact on confidentiality and integrity, and a high impact on availability.

Attack Vector:
NETWORK
Attack Complexity:
LOW
Privileges Required:
NONE
User Interaction:
NONE
Scope:
UNCHANGED
Confidentiality Impact:
NONE
Integrity Impact:
NONE
Availability Impact:
HIGH

Weakness Type

Allocation of Resources Without Limits or Throttling

The software allocates a reusable resource or group of resources on behalf of an actor without imposing any restrictions on the size or number of resources that can be allocated, in violation of the intended security policy for that actor.


Products Associated with CVE-2026-63075

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OpenSSL
 

Affected Versions

OpenSSL: