Summary
s2n-tls's mTLS API ordering may skip client authentication
Workarounds
Applications can workaround this issue by calling s2n_connection_set_config() after calling s2n_connection_set_client_auth_type(), or by enabling client authentication on the config with s2n_config_set_client_auth_type().
If you have any questions or comments about this advisory we ask that you contact AWS/Amazon Security via our vulnerability reporting page [2] or directly via email to [email protected]. Please do not create a public GitHub issue.
Impact
An API ordering issue in s2n-tls can cause client authentication to unexpectedly not be enabled on the server when it otherwise appears to be. Server applications are impacted if client authentication is enabled by calling s2n_connection_set_config() before calling s2n_connection_set_client_auth_type().
Applications are not impacted if these APIs are called in the opposite order, or if client authentication is enabled on the config with s2n_config_set_client_auth_type(). s2n-tls clients verifying server certificates are not impacted.
Impacted versions: < v1.5.0.
The application does not adequately verify the identity of a user, device, or process before granting access. Typical impact: unauthorized access to functions or data reserved for authenticated parties.
GHSA-857Q-XMPH-P2V5 has a CVSS score of 4.8 (Medium). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (0.3.0); upgrading removes the vulnerable code path.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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The patch is included in v1.5.0 [1].
Frequently Asked Questions
- What is GHSA-857Q-XMPH-P2V5? GHSA-857Q-XMPH-P2V5 is a medium-severity improper authentication vulnerability in s2n-tls (rust), affecting versions < 0.3.0. It is fixed in 0.3.0. The application does not adequately verify the identity of a user, device, or process before granting access.
- How severe is GHSA-857Q-XMPH-P2V5? GHSA-857Q-XMPH-P2V5 has a CVSS score of 4.8 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
- Which versions of s2n-tls are affected by GHSA-857Q-XMPH-P2V5? s2n-tls (rust) versions < 0.3.0 is affected.
- Is there a fix for GHSA-857Q-XMPH-P2V5? Yes. GHSA-857Q-XMPH-P2V5 is fixed in 0.3.0. Upgrade to this version or later.
- Is GHSA-857Q-XMPH-P2V5 exploitable, and should I be worried? Whether GHSA-857Q-XMPH-P2V5 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether GHSA-857Q-XMPH-P2V5 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix GHSA-857Q-XMPH-P2V5? Upgrade
s2n-tlsto 0.3.0 or later.