Summary
s2n-tls has a potentially observable differences in RSA premaster secret handling
When receiving a message from a client that sent an invalid RSA premaster secret, an issue in s2n-tls results in the server performing additional processing when the premaster secret contains an incorrect client hello version. While no practical attack on s2n-tls has been demonstrated, this causes a small timing difference which could theoretically be used as described in the Marvin Attack [1].
We would like to thank Hubert Kario [2] for reporting this issue.
Workarounds
Applications can work around this issue by using an s2n-tls security policy that disallows RSA key exchange.
If you have any questions or comments about this advisory we ask that you contact AWS/Amazon Security via our vulnerability reporting page [4] or directly via email to [email protected]. Please do not create a public GitHub issue.
[1] https://people.redhat.com/~hkario/marvin/
[2] https://github.com/tomato42
[3] https://github.com/aws/s2n-tls/releases/tag/v1.4.16
[4] https://aws.amazon.com/security/vulnerability-reporting
Impact
The extent of this issue is a timing difference. No practical attack on s2n-tls has been demonstrated.
This issue affects server applications that permit RSA key exchange. Applications that use the default, built-in blinding feature or properly implement self-service blinding are not affected.
Impacted versions: <= v1.4.15.
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 v1.4.16 [3].
Frequently Asked Questions
- What is GHSA-52XF-5P2M-9WRV? GHSA-52XF-5P2M-9WRV is a low-severity security vulnerability in s2n-tls (rust), affecting versions <= 0.2.6. It is fixed in 0.2.7.
- Which versions of s2n-tls are affected by GHSA-52XF-5P2M-9WRV? s2n-tls (rust) versions <= 0.2.6 is affected.
- Is there a fix for GHSA-52XF-5P2M-9WRV? Yes. GHSA-52XF-5P2M-9WRV is fixed in 0.2.7. Upgrade to this version or later.
- Is GHSA-52XF-5P2M-9WRV exploitable, and should I be worried? Whether GHSA-52XF-5P2M-9WRV 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-52XF-5P2M-9WRV 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-52XF-5P2M-9WRV? Upgrade
s2n-tlsto 0.2.7 or later.