CVE-2026-16318

QUIC Transport Parameters Memory Leak During HelloRetryRequest in s2n-tls

State: Published
Severity: 6.9 Medium
Published: Jul 21, 2026
Updated: Jul 22, 2026
Reserved: Jul 20, 2026

Description

The QUIC transport parameters extension handler in s2n-tls incorrectly uses s2n_alloc instead of s2n_realloc 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, s2n_alloc 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

Scores

CVSS	Score	Vector	Source
4.0	6.9 Medium	CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N	AMZN
3.1	5.3 Medium	CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L	AMZN

Weaknesses

CWE-401 Missing release of memory after effective lifetime

Affected Products

Product	Versions
s2n-tlsAmazon	v1.7.5 and earlierAffected

References

https://github.com/aws/s2n-tls/releases/tag/v1.7.6release-notespatch
https://staging.prod.website.marketing.aws.dev/security/security-bulletins/2026-062-aws/vendor-advisory
https://github.com/aws/s2n-tls/security/advisories/GHSA-cr7x-863j-xrc7release-notes

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