The s2n‑tls library fails to validate the outer content_type byte on TLS 1.3 encrypted records. Because the AEAD authentication tag covers only the payload, a malicious agent can change the outer content_type to a non‑application_data value. RFC 8446 demands that all outer content_type values be 0x17, so a modified record is still accepted by the peer, resulting in that record being silently discarded. This provides an active man‑in‑the‑middle with the ability to suppress one or more application data records, causing HTTP request/response desynchronization, corrupting write‑heavy workloads, and leading to undetectable data loss.

All versions of AWS s2n‑tls prior to v1.7.6 that support TLS 1.3 are impacted. The flaw exists in both client and server implementations. TLS 1.2 and QUIC connections are not affected, nor are other TLS libraries.

The vulnerability has a CVSS score of 8.3, indicating high severity for data integrity and availability. The EPSS score is below 1 %, showing a low likelihood of exploitation at present. The case is not listed in CISA KEV, implying no widespread known exploitation. An attacker requiring a man‑in‑the‑middle capable of tampering with TLS traffic can silently drop encrypted application data, but such conditions are relatively uncommon, keeping the overall risk moderate despite the high potential impact.