Missing validation of the outer contenttype 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 contenttype of all encrypted TLS 1.3 records must be applicationdata (0x17). The s2n-tls AEAD implementation hardcodes this value in the additional authenticated data rather than using the actual wire byte, so the outer contenttype 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 QUIC transport parameters extension handler in s2n-tls incorrectly uses s2nalloc instead of s2nrealloc 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, s2nalloc 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