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GHSA-5whh-4q9j-7v28
No affected components available
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 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
The vulnerability can be exploited over the network without needing physical access. It is difficult for an attacker to exploit this vulnerability and may require special conditions. An attacker does not need any special privileges or access rights. No user interaction is needed for the attacker to exploit this vulnerability. The impact is confined to the system where the vulnerability exists. There is a low impact on the availability of the system.
Limited exploitation activity has been observed. Close monitoring and planned remediation are recommended.
Probability that this vulnerability will be exploited in the wild within the next 30 days.
We did not find any exploit available. Neither in GitHub repositories nor in the Exploit-Database.
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