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8.6
CVE-2026-16317: s2n-tls can silently drop TLS 1.3 data records
CVE-2026-16317 · published 3 months ago
Summary
The Amazon s2n‑tls library that handles TLS 1.3 traffic may allow a man‑in‑the‑middle to discard individual encrypted messages without either side noticing. This can cause missing web requests or unnoticed data loss in applications that rely on TLS 1.3. Upgrade s2n‑tls to version 1.7.6 to fix the issue.
What to do
The CVE record does not list a fixed version. Check the vendor's site or the advisory links below - a fix may already be released.
Affected software
| Vendor | Product | Affected versions |
|---|---|---|
| aws | s2n-tls | <= 1.7.5 |
Original advisory text
Silent Drop of TLS 1.3 Encrypted Records in s2n-tls
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
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
References
- https://aws.amazon.com/security/security-bulletins/2026-062-aws/ Vendor Advisory
- https://github.com/aws/s2n-tls/releases/tag/v1.7.6 Patch
- https://github.com/aws/s2n-tls/security/advisories/GHSA-684c-v35q-fvx7 Vendor Advisory
- https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/16xxx/CVE-2026-16317... Vendor Advisory
- https://nvd.nist.gov/vuln/detail/CVE-2026-16317 Vendor Advisory
Internet-facing
60 days
Internal
At next upgrade
- Not known to be exploited
- Needs hands-on effort to exploit
- Gives an attacker partial control
Type
CWE-354Improper Validation of Integrity Check Value
Timeline
Published21 Jul 2026
Updated4 Nov 2026
First seen21 Jul 2026
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