Medium · published September 29, 2026
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.
| Product | Versions | Fixed in |
|---|---|---|
| openssl/openssl | ≥ 3.4.0, < 3.4.8 | 3.4.8 |
| openssl/openssl | ≥ 3.5.0, < 3.5.9 | 3.5.9 |
| openssl/openssl | ≥ 3.6.0, < 3.6.5 | 3.6.5 |
| openssl/openssl | ≥ 4.0.0, < 4.0.3 | 4.0.3 |