CVE-2026-16317

Received Received - Intake

Record Tampering in s2n-tls TLS 1.3 Implementation

Publication date: 2026-07-21

Last updated on: 2026-07-21

Assigner: AMZN

Description

Missing validation of the outer content_type byte on TLS 1.3 encrypted records in s2n-tls allows an active man-in-the-middle to silently discard individual application data records without either endpoint detecting the modification. RFC 8446 Section 5.2 requires that the outer content_type of all encrypted TLS 1.3 records must be application_data (0x17). The s2n-tls AEAD implementation hardcodes this value in the additional authenticated data rather than using the actual wire byte, so the outer content_type is not covered by the authentication tag. This enables selective suppression of application data. In HTTP pipelining scenarios, dropping a TLS record containing an HTTP request can cause request/response desynchronization, where subsequent responses are delivered to the wrong requests. In write-heavy workloads, a dropped record containing a write request can result in undetectable data loss when the client interprets a subsequent success response as confirmation of the dropped write. All TLS 1.3 connections are affected. Both TLS clients and servers are affected. TLS 1.2 and QUIC 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-2026-16317

Affected Vendors & Products

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

Helpful Resources

Exploitability

CWE

KEV

CWE ID	Description
CWE-354	The product does not validate or incorrectly validates the integrity check values or "checksums" of a message. This may prevent it from detecting if the data has been modified or corrupted in transmission.

Attack-Flow Graph

Executive Summary

This vulnerability involves missing validation of the outer content_type byte on TLS 1.3 encrypted records in s2n-tls. An attacker can silently discard application data records without detection by manipulating the outer content_type byte. The s2n-tls AEAD implementation does not authenticate this byte, allowing selective suppression of data.

Detection Guidance

This vulnerability cannot be reliably detected through standard network or system commands due to its nature as a protocol-level issue in TLS 1.3 implementation. The flaw involves missing validation of the outer content_type byte, which is not exposed in typical logs or monitoring tools. Detection would require specialized TLS inspection tools or custom monitoring of TLS 1.3 record handling.

Impact Analysis

This vulnerability can cause request/response desynchronization in HTTP pipelining, leading to wrong responses being delivered. In write-heavy workloads, it may result in undetectable data loss as clients assume dropped records were successfully processed.

Mitigation Strategies

Upgrade s2n-tls to version v1.7.6 or later immediately. This version includes the fix for the missing validation of the outer content_type byte in TLS 1.3 encrypted records. No other mitigation steps are recommended as the issue requires a code-level fix in the TLS library.

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