CVE-2026-16317 and CVE-2026-16318: Issues with s2n-tls: an open-source implementation of the TLS/SSL protocols
Two vulnerabilities have been identified in s2n-tls, an open-source TLS/SSL implementation. CVE-2026-16317 allows a man-in-the-middle to silently drop TLS 1.3 application data records without detection due to missing validation of the outer content_type byte. CVE-2026-16318 causes a memory leak in QUIC-enabled TLS 1.3 connections during HelloRetryRequest due to incorrect memory allocation handling. Both issues affect s2n-tls versions up to and including v1.7.5 and have been fixed in version v1.7.6.
AI Analysis
Technical Summary
CVE-2026-16317 involves s2n-tls failing to validate the outer content_type byte on TLS 1.3 encrypted records, allowing an active man-in-the-middle to silently drop individual application data records without detection. This is because the AEAD implementation hardcodes the content_type in the additional authenticated data rather than using the actual wire byte, leaving the outer content_type unauthenticated. All TLS 1.3 clients and servers using s2n-tls are affected; TLS 1.2 and QUIC are not affected by this issue. CVE-2026-16318 is a memory leak in the QUIC transport parameters extension handler caused by using s2n_alloc instead of s2n_realloc during HelloRetryRequest in TLS 1.3 connections with QUIC enabled. This leak occurs each time a QUIC-enabled TLS 1.3 connection undergoes HelloRetryRequest, potentially increasing memory consumption on long-running servers. Only QUIC-enabled deployments are affected. Both vulnerabilities affect s2n-tls versions up to and including v1.7.5 and have been addressed in version v1.7.6.
Potential Impact
CVE-2026-16317 allows an active man-in-the-middle attacker to silently drop TLS 1.3 application data records without detection by either endpoint, potentially disrupting communication without alerting the parties. CVE-2026-16318 causes a memory leak in QUIC-enabled TLS 1.3 connections during HelloRetryRequest, which can lead to increased memory consumption and potential resource exhaustion on long-running server processes. There is no indication of remote code execution or data disclosure from these vulnerabilities. TLS 1.2 and non-QUIC deployments are not affected by CVE-2026-16317 and CVE-2026-16318 respectively.
Mitigation Recommendations
A fixed version, s2n-tls v1.7.6, is available and addresses both vulnerabilities. It is recommended to upgrade to this version or later and ensure any forks or derivative code are patched accordingly. For CVE-2026-16317, no full workaround exists; configuring s2n-tls to use only TLS 1.2 avoids the affected code path but is not recommended due to loss of TLS 1.3 security benefits. For CVE-2026-16318, deployments not enabling QUIC are unaffected and require no action. QUIC-enabled deployments can temporarily mitigate memory leaks by periodically restarting server processes to reclaim leaked memory.
CVE-2026-16317 and CVE-2026-16318: Issues with s2n-tls: an open-source implementation of the TLS/SSL protocols
Description
Two vulnerabilities have been identified in s2n-tls, an open-source TLS/SSL implementation. CVE-2026-16317 allows a man-in-the-middle to silently drop TLS 1.3 application data records without detection due to missing validation of the outer content_type byte. CVE-2026-16318 causes a memory leak in QUIC-enabled TLS 1.3 connections during HelloRetryRequest due to incorrect memory allocation handling. Both issues affect s2n-tls versions up to and including v1.7.5 and have been fixed in version v1.7.6.
Affected software
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AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
CVE-2026-16317 involves s2n-tls failing to validate the outer content_type byte on TLS 1.3 encrypted records, allowing an active man-in-the-middle to silently drop individual application data records without detection. This is because the AEAD implementation hardcodes the content_type in the additional authenticated data rather than using the actual wire byte, leaving the outer content_type unauthenticated. All TLS 1.3 clients and servers using s2n-tls are affected; TLS 1.2 and QUIC are not affected by this issue. CVE-2026-16318 is a memory leak in the QUIC transport parameters extension handler caused by using s2n_alloc instead of s2n_realloc during HelloRetryRequest in TLS 1.3 connections with QUIC enabled. This leak occurs each time a QUIC-enabled TLS 1.3 connection undergoes HelloRetryRequest, potentially increasing memory consumption on long-running servers. Only QUIC-enabled deployments are affected. Both vulnerabilities affect s2n-tls versions up to and including v1.7.5 and have been addressed in version v1.7.6.
Potential Impact
CVE-2026-16317 allows an active man-in-the-middle attacker to silently drop TLS 1.3 application data records without detection by either endpoint, potentially disrupting communication without alerting the parties. CVE-2026-16318 causes a memory leak in QUIC-enabled TLS 1.3 connections during HelloRetryRequest, which can lead to increased memory consumption and potential resource exhaustion on long-running server processes. There is no indication of remote code execution or data disclosure from these vulnerabilities. TLS 1.2 and non-QUIC deployments are not affected by CVE-2026-16317 and CVE-2026-16318 respectively.
Mitigation Recommendations
A fixed version, s2n-tls v1.7.6, is available and addresses both vulnerabilities. It is recommended to upgrade to this version or later and ensure any forks or derivative code are patched accordingly. For CVE-2026-16317, no full workaround exists; configuring s2n-tls to use only TLS 1.2 avoids the affected code path but is not recommended due to loss of TLS 1.3 security benefits. For CVE-2026-16318, deployments not enabling QUIC are unaffected and require no action. QUIC-enabled deployments can temporarily mitigate memory leaks by periodically restarting server processes to reclaim leaked memory.
Technical Details
- Article Source
- {"url":"https://aws.amazon.com/security/security-bulletins/rss/2026-062-aws/","fetched":true,"fetchedAt":"2026-07-21T20:27:43.693Z","wordCount":378}
Threat ID: 6a5fd63f1010f89cc2274ba4
Added to database: 07/21/2026, 20:27:43 UTC
Last enriched: 07/21/2026, 20:27:56 UTC
Last updated: 07/21/2026, 21:06:36 UTC
Views: 17
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