What is CVE-2026-18140?

CVE-2026-18140 is a high-severity security vulnerability in aws-smithy-json (rust), affecting versions <= 0.62.6. It is fixed in 0.62.7.

How severe is CVE-2026-18140?

CVE-2026-18140 has a CVSS score of 7.5 (High). 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-smithy-json are affected by CVE-2026-18140?

aws-smithy-json (rust) versions <= 0.62.6 is affected.

Is there a fix for CVE-2026-18140?

Yes. CVE-2026-18140 is fixed in 0.62.7. Upgrade to this version or later.

Is CVE-2026-18140 exploitable, and should I be worried?

Whether CVE-2026-18140 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.

What actually determines whether CVE-2026-18140 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 CVE-2026-18140?

Upgrade aws-smithy-json to 0.62.7 or later.

CVE-2026-18140 in aws-smithy-json

Q: How severe is CVE-2026-18140?

CVE-2026-18140 has a CVSS score of 7.5 (High). 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.

Q: Which versions of aws-smithy-json are affected by CVE-2026-18140?

aws-smithy-json (rust) versions <= 0.62.6 is affected.

Q: Is there a fix for CVE-2026-18140?

Yes. CVE-2026-18140 is fixed in 0.62.7. Upgrade to this version or later.

Q: Is CVE-2026-18140 exploitable, and should I be worried?

Whether CVE-2026-18140 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.

Q: What actually determines whether CVE-2026-18140 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.

Q: How do I fix CVE-2026-18140?

Upgrade aws-smithy-json to 0.62.7 or later.

Summary

aws-smithy-json: Uncontrolled recursion in the aws-smithy-json unknown-key skip path allows unauthenticated remote denial of service in smithy-rs generated servers

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.

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 [email protected]. Please do not create a public GitHub issue.

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

CVE-2026-18140 has a CVSS score of 7.5 (High). 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 (0.62.7); upgrading removes the vulnerable code path.

Affected versions

aws-smithy-json (<= 0.62.6)

Security releases

aws-smithy-json → 0.62.7 (rust)

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.

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Remediation advice

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.

Frequently Asked Questions

What is CVE-2026-18140? CVE-2026-18140 is a high-severity security vulnerability in aws-smithy-json (rust), affecting versions <= 0.62.6. It is fixed in 0.62.7.
How severe is CVE-2026-18140? CVE-2026-18140 has a CVSS score of 7.5 (High). 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-smithy-json are affected by CVE-2026-18140? aws-smithy-json (rust) versions <= 0.62.6 is affected.
Is there a fix for CVE-2026-18140? Yes. CVE-2026-18140 is fixed in 0.62.7. Upgrade to this version or later.
Is CVE-2026-18140 exploitable, and should I be worried? Whether CVE-2026-18140 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 CVE-2026-18140 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 CVE-2026-18140? Upgrade aws-smithy-json to 0.62.7 or later.