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Unbounded Memory Growth in the QUIC PATH_CHALLENGE Handler

Unbounded Memory Growth in the QUIC PATH_CHALLENGE Handler (CVE-2026-34183)
Severity: Moderate

Issue summary: Remote peer may exhaust heap memory of the QUIC
server or client by flooding it with packets containing PATH_CHALLENGE
frames.

Impact summary: A malicious remote peer can cause an unbounded
memory allocation which can lead to an abnormal termination of the
application acting as a QUIC client or server and a Denial of Service.

A remote peer may exhaust heap memory by flooding the local
QUIC stack with PATH_CHALLENGE frames. The local QUIC stack
allocates a PATH_RESPONSE frame for every PATH_CHALLENGE it receives.
The allocated PATH_RESPONSE frame gets freed only when the remote
peer acknowledges reception of the PATH_RESPONSE frame which will
not be done by a malicious peer.

The FIPS modules in 4.0, 3.6, 3.5, 3.4, and 3.0 are not affected by
this issue. The QUIC stack is outside of OpenSSL FIPS module
boundary.

OpenSSL 3.4, 3.5, 3.6 and 4.0 are vulnerable to this issue.

OpenSSL 3.0, 1.1.1 and 1.0.2 are not affected by this issue.

OpenSSL 4.0 users should upgrade to OpenSSL 4.0.1
OpenSSL 3.6 users should upgrade to OpenSSL 3.6.3
OpenSSL 3.5 users should upgrade to OpenSSL 3.5.7
OpenSSL 3.4 users should upgrade to OpenSSL 3.4.6

The issue was reported by Abhinav Agarwal on 18th March 2026.

Fix suggested by Abhinav Agarwal, adapted by Alexandr Nedvedicky.