CVE-2026-18140: Uncontrolled recursion in the aws-smithy-json unknown-key skip path allows unauthenticated remote denial of service in smithy-rs generated servers
Summary Smithy-RS is a Rust code generation and runtime framework that generates HTTP clients and servers from Smithy interface definitions, powering the AWS SDK for Rust and custom service implementations. An issue exists which allows uncontrolled recursion in the unknown-key skip path of the Amazon aws-smithy-json runtime crate in versions 0.62.6 and earlier.
Impact Uncontrolled recursion in the unknown-key skip path of the aws-smithy-json runtime crate before 0.62.7, which the smithy-rs code generator invokes from every generated struct deserializer, might allow remote unauthenticated users to cause a denial of service (process abort via stack exhaustion) via a single small HTTP request containing deeply nested JSON to a smithy-rs generated server.
Impacted versions: aws-smithy-json <= 0.62.6
Patches This issue has been addressed in aws-smithy-json version 0.62.7. We recommend upgrading to the latest version and ensuring any forked or derivative code is patched to incorporate the new fixes.
Workarounds There are no workarounds besides updating to the patched version.
References If you have any questions or comments about this advisory, AWS asks that you contact [AWS/Amazon] Security via their vulnerability reporting page or directly via email to aws-security@amazon.com. Please do not create a public GitHub issue.
Other sources
Uncontrolled recursion in the unknown-key skip path of the aws-smithy-json runtime crate before 0.62.7, which the smithy-rs code generator invokes from every generated struct deserializer, might allow remote unauthenticated users to cause a denial of service (process abort via stack exhaustion) via a single small HTTP request containing deeply nested JSON to a smithy-rs generated server.
To remediate this issue, users should upgrade to aws-smithy-json 0.62.7 or later and rebuild.
— MITRE
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade
rust/aws-smithy-jsonto a version that resolves this vulnerability.Fixed in 0.62.7 - Upgrade
Upgrade
aws-smithy-jsonto a version that resolves this vulnerability.Fixed in 0.62.7 - Operational
Rebuild after upgrading aws-smithy-json to 0.62.7 or later.
Event History
Frequently Asked Questions
What is the severity of CVE-2026-18140?
CVE-2026-18140 has a high severity rating of 7.5.
How do I fix CVE-2026-18140?
To fix CVE-2026-18140, update the aws-smithy-json crate to version 0.62.7 or later.
What type of attack does CVE-2026-18140 allow?
CVE-2026-18140 allows unauthenticated remote denial of service via uncontrolled recursion.
Which software components are affected by CVE-2026-18140?
The affected components include aws-smithy-json and aws-smithy-rs generated servers.
When was CVE-2026-18140 published?
CVE-2026-18140 was published on July 30, 2026.