# CVE-2026-16317: Silent Drop of TLS 1.3 Encrypted Records in s2n-tls


- **Severity:** High 8.3 (`CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:H/VA:L/SC:N/SI:L/SA:N`)
- **Exploited in the wild:** Not known
- **Fix available:** Yes
- **Published:** 21 Jul 2026
- **Updated:** 22 Jul 2026
- **Also known as:** GHSA-684c-v35q-fvx7

## What is CVE-2026-16317?

CVE-2026-16317 is a high-severity vulnerability in AWS s2n-tls, published on 21 Jul 2026. 

### Official 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. 

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

Weakness: CWE-354 (Improper Validation of Integrity Check Value)

## Which versions are affected by CVE-2026-16317?


## How do I fix CVE-2026-16317?

Upgrade to a fixed version.

## Is CVE-2026-16317 being exploited?

There is no known exploitation of CVE-2026-16317 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-16317 and fix it if it is affected.

What it is: CVE-2026-16317 is a high-severity vulnerability in AWS s2n-tls, published on 21 Jul 2026. 
Exploitation: There is no known exploitation of CVE-2026-16317 in the wild and no public exploit code.

Affected product: AWS s2n-tls. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-16317/ (Markdown: https://insights.sbomify.com/CVE-2026-16317/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-16317
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-16317
- OSV: https://osv.dev/vulnerability/CVE-2026-16317

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-16317/
Summaries are generated and may contain mistakes; the official description above is the record.