AWS s2n-tls up to 1.7.5 AEAD implementation outer content_type input validation

Summaryinfo

A vulnerability was found in AWS s2n-tls up to 1.7.5 and classified as problematic. This affects an unknown function of the component AEAD implementation. Executing a manipulation of the argument outer content_type can lead to input validation. This vulnerability is registered as CVE-2026-16317. It is possible to launch the attack remotely. No exploit is available.

Detailsinfo

A vulnerability classified as problematic was found in AWS s2n-tls up to 1.7.5. This vulnerability affects an unknown code of the component AEAD implementation. The manipulation of the argument outer content_type with an unknown input leads to a input validation vulnerability. The CWE definition for the vulnerability is CWE-20. The product receives input or data, but it does not validate or incorrectly validates that the input has the properties that are required to process the data safely and correctly. As an impact it is known to affect integrity, and availability. CVE summarizes:

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

The advisory is available at github.com. This vulnerability was named CVE-2026-16317 since 07/20/2026. The exploitation appears to be easy. The attack can be initiated remotely. Technical details are known, but there is no available exploit.

Upgrading to version 1.7.6 eliminates this vulnerability.

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Productinfo

Vendor

• AWS

Name

• s2n-tls

Version

• 1.7.0
• 1.7.1
• 1.7.2
• 1.7.3
• 1.7.4
• 1.7.5

Website

• Product: https://github.com/aws/s2n-tls/

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