CVE-2026-34183: Unbounded Memory Growth in the QUIC PATH_CHALLENGE Handler

Severity: high (CVSS 7.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 1.0% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-06-09 · updated 2026-07-23
Weakness: CWE-1325

Description

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.

Affected products

OpenSSL: from 3.4.0 before 3.4.6; from 3.5.0 before 3.5.7; from 3.6.0 before 3.6.3; 4.0.0 — fixed in 3.4.6, 3.5.7, 3.6.3

How to fix

Upgrade to a fixed version: OpenSSL 3.4.6, 3.5.7, 3.6.3. Check the vendor advisory for mitigations.

References

Get alerted when CVE-2026-34183 or the next vulnerability affects your stack