Executive brief
OpenSSL is a widely used security library that provides encrypted communications for websites and applications. A flaw in its QUIC protocol implementation allows a remote attacker to crash a server or client by flooding it with specific network requests. This results in a denial-of-service, potentially taking affected services offline.
Technical details
A vulnerability exists in the OpenSSL QUIC stack due to improper management of PATH_RESPONSE frames. When a local QUIC stack receives a PATH_CHALLENGE frame, it allocates a corresponding PATH_RESPONSE frame. These allocations are only freed upon receipt of an acknowledgment from the remote peer. A malicious actor can flood the target with PATH_CHALLENGE frames while withholding acknowledgments, leading to unbounded heap memory growth and eventual process termination (Denial of Service). The issue affects OpenSSL versions 3.4 through 4.0; FIPS modules are not impacted as the QUIC stack resides outside the FIPS boundary. Users should upgrade to versions 4.0.1, 3.6.3, 3.5.7, or 3.4.6.
Affected products
- OpenSSL Foundation OpenSSL 4.0, 3.6, 3.5, 3.4
Timeline
- 2026-03-18: disclosed: Reported by Abhinav Agarwal
- 2026-06-09: advisory: Official OpenSSL Security Advisory published
References
- https://github.com/openssl/security/commit/5b306efb0b3779dfdd0803b4afc9d08c91f11517
- https://github.com/openssl/security/commit/7d06955ebe0ecf8adfd4c1e92018586da47ef9ac
- https://github.com/openssl/security/commit/d2e9efbe4900a373227deb136e8665401404ffac
- https://github.com/openssl/security/commit/fbaa83859c01ad64f497b757aaf51be7d05ed9eb
- https://openssl-library.org/news/secadv/20260609.txt