CVE-2026-16318: QUIC Transport Parameters Memory Leak During HelloRetryRequest in s2n-tls
The QUIC transport parameters extension handler in s2n-tls incorrectly uses s2nalloc instead of s2nrealloc to store the peer's transport parameters. When a TLS 1.3 connection goes through a HelloRetryRequest, the handler is called twice on the same connection. On the second call, s2nalloc zeroes the existing pointer before allocating new memory, causing the first allocation to be leaked.
This can occur during normal QUIC traffic when a client offers a key share group the server does not prefer. An unauthenticated user can amplify the issue by deliberately forcing HelloRetryRequests, causing up to approximately 64 KB of unreachable memory per handshake. Over time, this can lead to increased memory consumption on long-running server processes. The unreachable memory is only reclaimed when the process is restarted.
Only server-side QUIC-enabled deployments are affected. Non-QUIC TLS connections are not affected.
We recommend you upgrade s2n-tls to version v1.7.6
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade
s2n-tlsto a version that resolves this vulnerability.Fixed in v1.7.6Patch QUIC Transport Parameters Memory Leak During HelloRetryRequest in s2n-tls - Operational
Restart the long-running server process to reclaim the unreachable memory associated with the QUIC transport parameters memory leak (unreachable memory is only reclaimed when the process is restarted).
Event History
Frequently Asked Questions
What is the severity of CVE-2026-16318?
CVE-2026-16318 has a medium severity rating of 6.9.
How do I fix CVE-2026-16318?
To fix CVE-2026-16318, update to the latest version of AWS s2n-tls that addresses this vulnerability.
What is the risk associated with CVE-2026-16318?
The risk associated with CVE-2026-16318 is rated at 33, indicating a moderate level of concern.
What type of systems are affected by CVE-2026-16318?
CVE-2026-16318 affects AWS s2n-tls implementations handling QUIC transport parameters.
What vulnerability does CVE-2026-16318 describe?
CVE-2026-16318 describes a memory leak in the QUIC transport parameters extension handler during HelloRetryRequest in s2n-tls.