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s2n-tls CVE-2026-16318

| EUVDEUVD-2026-46402 MEDIUM
Memory Leak (CWE-401)
2026-07-21 AMZN
Information Disclosure Suse Amazon S2N Tls
6.9
CVSS 4.0 · Vendor: AMZN
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Severity by source

Vendor (AMZN) PRIMARY
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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
vuln.today AI
5.3 MEDIUM

Network vector and no privileges required confirmed; AC:L because forcing HRR needs only advertising unsupported key shares; availability impact is Low given slow, non-immediate exhaustion.

3.1 AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
4.0 AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N
SUSE
5.3 MEDIUM
AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

Primary rating from Vendor (AMZN).

CVSS VectorVendor: AMZN

Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
X

Lifecycle Timeline

3
CVSS changed
Jul 21, 2026 - 21:22 NVD
5.3 (MEDIUM) 6.9 (MEDIUM)
Source Code Evidence Fetched
Jul 21, 2026 - 21:08 vuln.today
Analysis Generated
Jul 21, 2026 - 21:08 vuln.today

DescriptionCVE.org

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

AnalysisAI

Memory leak in Amazon s2n-tls's QUIC transport parameters handler exposes server-side QUIC deployments to gradual heap exhaustion by unauthenticated remote clients. The flaw is rooted in incorrect allocator use during TLS 1.3 HelloRetryRequest (HRR) flows - a standard protocol exchange that can be deliberately forced by clients advertising key share groups the server will reject - causing up to approximately 64 KB of unreachable memory per handshake. No active exploitation or public exploit code has been identified; vendor-confirmed patch v1.7.6 is available.

Technical ContextAI

s2n-tls (CPE: cpe:2.3:a:amazon:s2n-tls:*:*:*:*:*:*:*:*) is Amazon's open-source TLS implementation used across AWS services and by downstream integrators. The QUIC transport parameters extension handler processes the quic_transport_parameters TLS extension negotiated during QUIC connection establishment. CWE-401 (Missing Release of Memory after Effective Lifetime) is the precise root cause: during a TLS 1.3 handshake that triggers a HelloRetryRequest, the handler is invoked twice on the same connection object. The first invocation allocates memory via s2n_alloc. The second invocation incorrectly calls s2n_alloc again rather than s2n_realloc; s2n_alloc zeroes the stored pointer before allocating fresh memory, silently orphaning the first allocation without freeing it. The leaked memory is unreachable until the process is restarted. Only the QUIC code path is affected - standard TLS connections that do not use the QUIC transport parameters extension are entirely immune.

RemediationAI

Upgrade s2n-tls to v1.7.6 or later; the patched release is available at https://github.com/aws/s2n-tls/releases/tag/v1.7.6 and documented in the AWS security bulletin at https://staging.prod.website.marketing.aws.dev/security/security-bulletins/2026-062-aws/ (note: this URL appears to be a staging endpoint - verify direct availability from the GitHub advisory). If immediate patching is not feasible, the most effective compensating control is to disable QUIC support on the affected server, reverting to TLS-only operation; this eliminates the vulnerable code path entirely but requires dropping HTTP/3 and QUIC-based traffic, impacting performance-sensitive applications that rely on QUIC's latency advantages. As a short-term operational measure for environments with scheduled maintenance windows, periodic process restarts will reclaim all accumulated leaked memory, though this does not prevent ongoing leakage between cycles and should not substitute for patching.

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Vendor StatusVendor

SUSE

Severity: Moderate
Product Status
openSUSE Leap 16.0 Fixed
SUSE Linux Enterprise High Performance Computing 12 Not-Affected
SUSE Linux Enterprise High Performance Computing 15 SP7 Affected
SUSE Linux Enterprise Module for Public Cloud 15 SP7 Affected
SUSE Linux Enterprise Server 15 SP7 Affected

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CVE-2026-16318 vulnerability details – vuln.today
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