CVE-2026-42772 Potential CPU DoS via O(n^2) Fragment Reassembly in QUIC
Remote attackers can cause CPU exhaustion and denial of service in OpenSSL QUIC implementations by sending out-of-order stream frames.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-42772?
CVE-2026-42772 is a medium-severity denial of service vulnerability in Openssl Openssl, published on 29 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
Issue summary: The QUIC stream reassembly algorithm performance deteriorates progressively as packets are arriving out of order. The worst case has a quadratic complexity proportional to the number of stream frames kept in the buffer for the received stream data.
Impact summary: A remote QUIC peer that completes the handshake can create a connection-scoped CPU pressure and potentially a Denial of Service using compliant STREAM frames inside the advertised receive window, with low attacker bandwidth.
CWE: CWE-407: Inefficient Algorithmic Complexity
Description: OpenSSL manages received QUIC stream fragments using a doubly-linked list. While it optimizes for append operations (at the end of the list), it falls back to a head-to-tail linear search for any fragment that does not immediately follow the current `tail`.
By manipulating the sequence of offsets, an attacker can force the server to perform O(n^2) operations, consuming excessive CPU time for the QUIC process.
FIPS impact: no The FIPS module is not affected as the QUIC implementation is outside of the OpenSSL FIPS module boundary.
Weakness: CWE-407
Which versions are affected by CVE-2026-42772?
It affects 1 product.
Products include Openssl Openssl.
How do I fix CVE-2026-42772?
Apply the vendor's patch.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-42772 being exploited?
There is no known exploitation of CVE-2026-42772 in the wild and no public exploit code.
Other vulnerabilities in Openssl Openssl
Sources
Also known as AZL-105456, AZL-105525, AZL-105579, AZL-105630, AZL-105828, AZL-105876 and 6 more.