CVE-2026-16317
Severity CVSS v4.0:
HIGH
Type:
Unavailable / Other
Publication date:
21/07/2026
Last modified:
22/07/2026
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. <br />
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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.<br />
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All TLS 1.3 connections are affected. Both TLS clients and servers are affected. TLS 1.2 and QUIC connections are not affected.<br />
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We recommend you upgrade s2n-tls to version v1.7.6
Impact
Base Score 4.0
8.30
Severity 4.0
HIGH
Base Score 3.x
6.50
Severity 3.x
MEDIUM