Summary
aws-kms-tls-auth vulnerable to memory overallocation
aws-kms-tls-auth is an optional utility for s2n-tls that enables customers to use AWS KMS keys as part of the PSK extension field in a TLS 1.3 handshake. An issue exists in this library that can lead to overallocation of memory potentially resulting in a denial of service.
Workarounds
There is no workaround. Applications using aws-kms-tls-auth should upgrade to the most recent release.
Acknowledgement
s2n-tls would like to thank Joshua Rogers (https://joshua.hu/) of AISLE Research Team (https://aisle.com/) for collaborating on this issue through the coordinated disclosure process.
If there are any questions or comments about this advisory, contact AWS/Amazon Security via the vulnerability reporting page [2] or directly via email to [email protected]. Please do not create a public GitHub issue.
[1] https://crates.io/crates/aws-kms-tls-auth/0.0.3
[2] Vulnerability reporting page: https://aws.amazon.com/security/vulnerability-reporting
Impact
The PSK extension field in TLS 1.3 uses length-prefixed lists to encode variable-length data. aws-kms-tls-auth interprets the length prefix incorrectly resulting in additional memory allocation.
s2n-tls limits ClientHello messages to 64 KB. Due to this issue, the server may allocate up to 10× the received size, meaning a single message could trigger an allocation of up to 640 KB. Repeated allocations of this size could exhaust server resources and lead to a denial-of-service.
No AWS services are affected. Applications should continue to follow best practices by limiting the number of in-flight handshakes and concurrent connections. Applications using the aws-kms-tls-auth crate should upgrade to version 0.0.3.
Impacted versions: < 0.0.3
GHSA-5WHH-4Q9J-7V28 has a CVSS score of 3.7 (Low). 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 (0.0.3); 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.
Already deployed Kodem?
See it in your environmentNew to Kodem? Get a demo →Remediation advice
This issue has been addressed in aws-kms-tls-auth v0.0.3 [1].
Frequently Asked Questions
- What is GHSA-5WHH-4Q9J-7V28? GHSA-5WHH-4Q9J-7V28 is a low-severity security vulnerability in aws-kms-tls-auth (rust), affecting versions < 0.0.3. It is fixed in 0.0.3.
- How severe is GHSA-5WHH-4Q9J-7V28? GHSA-5WHH-4Q9J-7V28 has a CVSS score of 3.7 (Low). 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 aws-kms-tls-auth are affected by GHSA-5WHH-4Q9J-7V28? aws-kms-tls-auth (rust) versions < 0.0.3 is affected.
- Is there a fix for GHSA-5WHH-4Q9J-7V28? Yes. GHSA-5WHH-4Q9J-7V28 is fixed in 0.0.3. Upgrade to this version or later.
- Is GHSA-5WHH-4Q9J-7V28 exploitable, and should I be worried? Whether GHSA-5WHH-4Q9J-7V28 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-5WHH-4Q9J-7V28 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-5WHH-4Q9J-7V28? Upgrade
aws-kms-tls-authto 0.0.3 or later.