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3.7
AWS KMS TLS Auth library may cause system crashes
GHSA-5whh-4q9j-7v28
Summary
A bug in the AWS KMS TLS Auth library can cause a server to run out of memory, leading to a system crash. This can happen when a malicious client sends a large message to the server. To fix this, update the library to the latest version, 0.0.3.
What to do
- Update aws-kms-tls-auth to version 0.0.3.
Affected software
| Vendor | Product | Affected versions | Fix available |
|---|---|---|---|
| – | aws-kms-tls-auth | <= 0.0.3 | 0.0.3 |
Original title
aws-kms-tls-auth vulnerable to memory overallocation
Original description
### Summary
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.
### 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
### Patches
This issue has been addressed in aws-kms-tls-auth v0.0.3 [1].
### 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]](mailto:[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
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.
### 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
### Patches
This issue has been addressed in aws-kms-tls-auth v0.0.3 [1].
### 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]](mailto:[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
ghsa CVSS3.1
3.7
Vulnerability type
CWE-119
Buffer Overflow
Published: 3 Mar 2026 · Updated: 7 Mar 2026 · First seen: 6 Mar 2026