Issues with s2n-tls: an open-source implementation of the TLS/SSL protocols

Bulletin ID: 2026-062-AWS Scope: AWS Content Type: Important (requires attention) Publication Date: 07/21/2026 13:00 PM PDT Description: s2n-tls is an open source C99 implementation of the TLS/SSL protocol. We have identified two distinct issues: CVE-2026-16317 : 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 drop 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. All TLS 1.3 connections are affected. Both TLS clients and servers are affected. TLS 1.2 and QUIC connections are not affected. CVE-2026-16318 : QUIC Transport Parameters Memory Leak During HelloRetryRequest in s2n-tls Incorrect use of s2n_alloc instead of s2n_realloc in the QUIC transport parameters extension handler in s2n-tls causes one memory allocation to be leaked each time a QUIC-enabled TLS 1.3 connection goes through a HelloRetryRequest. This can occur during normal handshakes when a client offers a key share group the server does not prefer, and can lead to increased memory consumption on long-running server processes. Only QUIC-enabled deployments are affected. Impacted versions:   Resolution: These issues have been addressed in s2n-tls version v1.7.6 . We recommend upgrading to the latest version and ensuring any forked or derivative code is patched to incorporate the new fixes. Workarounds: For CVE-2026-16317 (Silent Drop of TLS 1.3 Encrypted Records), there is no workaround that fully mitigates this issue. Configuring s2n-tls to use only TLS 1.2 security policies would avoid the affected code path, but this is not recommended as it removes the security benefits of TLS 1.3. For CVE-2026-16318 (QUIC Transport Parameters Memory Leak During HelloRetryRequest), deployments that do not enable QUIC are not affected and do not require any action. For QUIC-enabled deployments, restarting server processes periodically can reclaim the unreachable memory as a temporary mitigation. References: CVE-2026-16317 CVE-2026-16318 GHSA-cr7x-863j-xrc7 GHSA-684c-v35q-fvx7 Please email aws-security@amazon.com with any security questions or concerns. "},"metadata":{"tags":[]}},{"fields":{"patternBoolean2":"false","id":"ams#rt-rich-textc2#pattern-data"},"metadata":{"tags":[{"name":"pattern-data","description":"Default pattern data","id":"ams#rt-rich-textc2#pattern-data","namespaceId":"rt-rich-text"}]}}]},"metadata":{"auth":{},"testAttributes":{}},"context":{"page":{"pageUrl":"https://aws.amazon.com/security/security-bulletins/2026-062-aws/"},"contentType":"page","environment":{"stage":"prod","region":"us-west-2"},"sdkVersion":"2.0.27"},"refMap":{"manifest.js":"cda3e8d042","rt-rich-text.js":"5043b0a87f","rt-rich-text.rtl.css":"6a04028f86","rt-rich-text.css":"98f5a6aee4","rt-rich-text.css.js":"3d619cc2e1","rt-rich-text.rtl.css.js":"ccdb945d3e"},"settings":{"templateMappings":{"patternHeading":"patternHeading","patternSubheading":"patternSubheading","patternDark":"patternBoolean2","title":"itemHeading","bodyText":"itemLongLoc"}}} CVE-2026-16317 and CVE-2026-16318: Issues with s2n-tls: an open-source implementation of the TLS/SSL protocols Bulletin ID: 2026-062-AWS Scope: AWS Content Type: Important (requires attention) Publication Date: 07/21/2026 13:00 PM PDT Description: s2n-tls is an open source C99 implementation of the TLS/SSL protocol. We have identified two distinct issues: CVE-2026-16317 : 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

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CVE-2026-16318

• aws.amazon.com/security/security-bulletins/rss/2026-062-aws/
• www.cve.org/CVERecord?id=CVE-2026-16317
• www.cve.org/CVERecord?id=CVE-2026-16318