CVE-2026-84784: OpenSSL QUIC denial of service via NEW_CONNECTION_ID frame flooding

CVE-2026-84784 · Severity: high · CVSS 7.5 · Published 2026-09-29

OpenSSL's QUIC implementation, which enables encrypted communication for modern applications, contains a flaw that allows a remote attacker to exhaust server memory by flooding it with connection ID management frames. An attacker can force the server to allocate up to 400MB of memory that cannot be released without first acknowledging the attacker's traffic, creating a denial of service condition that could crash the server or make it unavailable to legitimate users.

Technologies: OpenSSL. Vendors: OpenSSL.

Quick answers

Is CVE-2026-84784 exploited in the wild?
No. Junglewise Threat Intelligence has no report of CVE-2026-84784 being exploited in the wild.
How severe is CVE-2026-84784?
High severity, with a CVSS score of 7.5, published 29 September 2026.
Which products and versions are affected?
OpenSSL OpenSSL.
Is there a fix for CVE-2026-84784?
No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.
How is CVE-2026-84784 attacked?
It is attacked over the network, in a software library.
Am I affected by CVE-2026-84784?
Check whether you run OpenSSL. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

Technical details

The vulnerability is a resource exhaustion issue (CWE-770) in QUIC connection ID handling. A remote peer sends NEW_CONNECTION_ID frames which trigger the local stack to generate RETIRE_CONNECTION_ID frames queued in the Control Frame Queue; if the attacker withholds ACKs, these frames accumulate without being freed. The flaw stems from the OpenSSL QUIC stack retiring destination CIDs upon frame receipt rather than waiting for ACK confirmation, bypassing the limit on connection IDs per RFC 9000.

Affected products

  • OpenSSL OpenSSL

Timeline

  • 2026-09-29: disclosed

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