Memory overallocation in aws-kms-tls-auth
Low3.7Published Mar 2, 2026
### 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-a...
Affected versions
| Package | Affected | Fixed in |
|---|---|---|
| aws-kms-tls-auth crates.io | < 0.0.3 | 0.0.3 |
Details and references
### 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 We 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 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 [aws-security@amazon.com](mailto:aws-security@amazon.com). 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
- CVSS 3.1
- CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L
- Severity from
- GitHub (reviewed advisory)
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