CVE-2026-16318

Received Received - Intake

Memory Leak in s2n-tls QUIC Transport Parameters

Publication date: 2026-07-21

Last updated on: 2026-07-21

Assigner: AMZN

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

CVSS Scores

EPSS Scores

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Meta Information

Published

2026-07-21

Last Modified

2026-07-21

Generated

2026-07-22

AI Q&A

2026-07-22

EPSS Evaluated

N/A

NVD

CVE-2026-16318

Affected Vendors & Products

Vendor	Product	Version / Range
aws	s2n-tls	v1.7.6

Helpful Resources

Exploitability

CWE

KEV

CWE ID	Description
CWE-401	The product does not sufficiently track and release allocated memory after it has been used, making the memory unavailable for reallocation and reuse.

Attack-Flow Graph

Executive Summary

This vulnerability involves a memory leak in the QUIC transport parameters extension handler of s2n-tls. When a TLS 1.3 connection undergoes a HelloRetryRequest, the handler is called twice. The second call uses s2n_alloc, which zeroes the existing memory allocation before creating a new one, causing the first allocation to be leaked. An attacker can force HelloRetryRequests to amplify this issue, leading to up to 64 KB of unreachable memory per handshake. This increases memory consumption on long-running server processes until a restart reclaims the memory.

Detection Guidance

This vulnerability is specific to s2n-tls QUIC server deployments and may not have direct detection commands. Monitor memory usage on QUIC-enabled servers for gradual increases, which could indicate memory leaks. Check s2n-tls version with 's2n-tls --version' to confirm if you're running a vulnerable version.

Impact Analysis

If you run a server using s2n-tls with QUIC enabled, this vulnerability can cause increased memory usage over time. This may lead to degraded performance or crashes due to memory exhaustion. The impact is limited to QUIC-enabled server deployments; non-QUIC TLS connections are unaffected.

Mitigation Strategies

Upgrade s2n-tls to version v1.7.6 or later immediately. Restart affected QUIC server processes to reclaim leaked memory. Disable QUIC temporarily if an upgrade isn't immediately possible, though this may impact services.

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