What is CVE-2026-16756?

CVE-2026-16756 is a high-severity allocation of resources without limits or throttling vulnerability in aws-smithy-http-server (rust), affecting versions <= 0.66.4. It is fixed in 0.66.5. The application allocates resources such as memory, threads, or file descriptors based on untrusted input without enforcing a cap.

How severe is CVE-2026-16756?

CVE-2026-16756 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-http-server are affected by CVE-2026-16756?

aws-smithy-http-server (rust) versions <= 0.66.4 is affected.

Is there a fix for CVE-2026-16756?

Yes. CVE-2026-16756 is fixed in 0.66.5. Upgrade to this version or later.

Is CVE-2026-16756 exploitable, and should I be worried?

Whether CVE-2026-16756 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-2026-16756 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-2026-16756?

Upgrade aws-smithy-http-server to 0.66.5 or later.

CVE-2026-16756 in aws-smithy-http-server

Q: How severe is CVE-2026-16756?

CVE-2026-16756 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-http-server are affected by CVE-2026-16756?

aws-smithy-http-server (rust) versions <= 0.66.4 is affected.

Q: Is there a fix for CVE-2026-16756?

Yes. CVE-2026-16756 is fixed in 0.66.5. Upgrade to this version or later.

Q: Is CVE-2026-16756 exploitable, and should I be worried?

Whether CVE-2026-16756 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-2026-16756 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-2026-16756?

Upgrade aws-smithy-http-server to 0.66.5 or later.

Summary

Smithy-RS: Allocation of resources without limits in the default aws-smithy-http-server serve() path allows unauthenticated Slowloris denial of service

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 where, under certain circumstances, allocation of resources without limits in the default aws-smithy-http-server serve() path allows unauthenticated Slowloris denial of service.

Workarounds

There is no workaround besides updating to the patched version.

Contact

If you have any questions or comments about this advisory, AWS asks that you contact AWS Security via the vulnerability reporting page or directly via email to [email protected]. Please do not create a public GitHub issue.

Impact

Missing connection and header-read timeouts and the absence of a concurrent-connection cap in the default serve() path of Amazon aws-smithy-http-server might allow remote attackers to cause a denial of service by opening many connections and sending partial requests that are never completed, exhausting server sockets and tasks.

Impacted versions: aws-smithy-http-server <= 0.66.4

The application allocates resources such as memory, threads, or file descriptors based on untrusted input without enforcing a cap. Typical impact: resource exhaustion leading to denial of service.

CVE-2026-16756 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 (0.66.5); upgrading removes the vulnerable code path.

Affected versions

aws-smithy-http-server (<= 0.66.4)

Security releases

aws-smithy-http-server → 0.66.5 (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-http-server version 0.66.5. AWS recommends 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-2026-16756? CVE-2026-16756 is a high-severity allocation of resources without limits or throttling vulnerability in aws-smithy-http-server (rust), affecting versions <= 0.66.4. It is fixed in 0.66.5. The application allocates resources such as memory, threads, or file descriptors based on untrusted input without enforcing a cap.
How severe is CVE-2026-16756? CVE-2026-16756 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-http-server are affected by CVE-2026-16756? aws-smithy-http-server (rust) versions <= 0.66.4 is affected.
Is there a fix for CVE-2026-16756? Yes. CVE-2026-16756 is fixed in 0.66.5. Upgrade to this version or later.
Is CVE-2026-16756 exploitable, and should I be worried? Whether CVE-2026-16756 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-2026-16756 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-2026-16756? Upgrade aws-smithy-http-server to 0.66.5 or later.