CVE-2026-16756: Smithy-RS Remote Code Execution Vulnerability

HIGH
Advisory Identifier: GHSA-jvxp-qmx7-gjpx
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CVSS 7.5
CWE-770
Published
Advisory Summary

CVE-2026-16756 is a HIGH (CVSS 7.5) remote code execution vulnerability (CWE-770: Allocation of Resources Without Limits or Throttling) affecting Smithy-RS libraries in the crates.io ecosystem. The issue involves allocation of resources without limits in the default aws-smithy-http-server serve() path allows unauthenticated slowloris denial of service. Remediation is available by upgrading affected packages to version 0.66.5.

CVE-2026-16756 at a Glance

CVE Identifier CVE-2026-16756
GHSA Identifier GHSA-jvxp-qmx7-gjpx
Severity HIGH
CVSS v3.1 Base Score 7.5
CWE Classification CWE-770: Allocation of Resources Without Limits or Throttling
Affected Product Smithy-RS
Package Ecosystem crates.io
Published Date
Last Updated

Security Impact

CVSS: 7.5

The security impact metrics below are parsed directly from the CVSS v3.1 vector string (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H).

Attack Vector Network (AV:N)
Attack Complexity Low (AC:L)
Privileges Required None (PR:N)
User Interaction None (UI:N)
Scope Unchanged (S:U)
Confidentiality None (C:N)
Integrity None (I:N)
Availability High (A:H)

How to Fix CVE-2026-16756

To remediate this vulnerability, upgrade all affected Smithy-RS dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.

aws-smithy-http-server fixed: 0.66.5 
Upgrade aws-smithy-http-server to 0.66.5
Verify Direct and Transitive Dependencies

Run the following command in your project directory to verify that all resolved dependencies use the patched release: 

inspect dependencies for aws-smithy-http-server

How to Check if You Are Affected

To determine whether your application is affected by CVE-2026-16756, inspect your project dependencies for Smithy-RS:

inspect dependencies for aws-smithy-http-server

Analyze the terminal output to locate any version of Smithy-RS in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 0.66.5), your application is affected.

Note: Verify declared build manifests and deployed runtime container environments.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-770: Allocation of Resources Without Limits or Throttling, where the product allocates a reusable resource or group of resources on behalf of an actor without imposing any intended restrictions on the size or number of resources that can be allocated. In Smithy-RS, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.

Source Advisory Statement

## 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 where, under certain circumstances, allocation of resources without limits in the default aws-smithy-http-server serve() path allows unauthenticated Slowloris denial of service. ## 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 ## Patches 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. ## 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](https://aws.amazon.com/security/vulnerability-reporting) or directly via email to [aws-security@amazon.com](mailto:aws-security@amazon.com). Please do not create a public GitHub issue.

CVE-2026-16756 Affected Smithy-RS Versions

1 component(s)
Fixed Versions:
0.66.5
Product / Package Ecosystem Affected Versions Fixed Version
aws-smithy-http-server
 crates.io
< 0.66.5
0.66.5

References

GitHub Advisory / Wiki ADVISORY
https://github.com/smithy-lang/smithy-rs/security/advisories/GHSA-jvxp-qmx7-gjpx
NVD — CVE-2026-16756 NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-16756
Smithy-RS Security Information SECURITY
https://aws.amazon.com/security/security-bulletins/2026-064-aws
crates.io/crates/aws-smithy-h... WEB
https://crates.io/crates/aws-smithy-http-server/0.66.5
Smithy-RS Source Repository REPOSITORY
https://github.com/smithy-lang/smithy-rs

Frequently Asked Questions

What is CVE-2026-16756?
CVE-2026-16756 is a security vulnerability in Smithy-RS involving Allocation of resources without limits in the default aws-smithy-http-server serve() path allows unauthenticated Slowloris denial of service under CWE-770: Allocation of Resources Without Limits or Throttling.
Which Smithy-RS versions are affected?
Affected versions include releases prior to 0.66.5 across affected packages: aws-smithy-http-server.
What version fixes CVE-2026-16756?
Upgrading to 0.66.5 (or the latest patched release for your respective branch) resolves the vulnerability.
Is aws-smithy-http-server affected?
Yes, aws-smithy-http-server is affected in releases prior to 0.66.5. Upgrade your dependency to 0.66.5 or later.
What is the CVSS score of CVE-2026-16756?
CVE-2026-16756 has a CVSS v3.1 base score of 7.5 (HIGH) with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H.
What CWE is associated with CVE-2026-16756?
CVE-2026-16756 is classified under CWE-770: Allocation of Resources Without Limits or Throttling (The product allocates a reusable resource or group of resources on behalf of an actor without imposing any intended restrictions on the size or number of resources that can be allocated.).
How can I check crates.io dependencies for CVE-2026-16756?
Run the dependency tree command: 'inspect dependencies for aws-smithy-http-server'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.
Machine-readable OSV JSON OSV v1.5 Schema
Normalized schema output
View Raw JSON 
{
  "schema_version" : "1.4.0",
  "id" : "GHSA-jvxp-qmx7-gjpx",
  "modified" : "2026-07-24T22:37:39Z",
  "published" : "2026-07-24T22:37:39Z",
  "aliases" : [ "CVE-2026-16756" ],
  "summary" : "Smithy-RS: Allocation of resources without limits in the default aws-smithy-http-server serve() path allows unauthenticated Slowloris denial of service",
  "details" : "## Summary\nSmithy-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. \n\n## Impact\nMissing 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.\n\nImpacted versions: aws-smithy-http-server <= 0.66.4\n\n## Patches\nThis 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.\n\n## Workarounds\nThere is no workaround besides updating to the patched version.\n\n## Contact\nIf you have any questions or comments about this advisory, AWS asks that you contact AWS Security via the [vulnerability reporting page](https://aws.amazon.com/security/vulnerability-reporting) or directly via email to [aws-security@amazon.com](mailto:aws-security@amazon.com). Please do not create a public GitHub issue.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H"
  }, {
    "type" : "CVSS_V4",
    "score" : "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "crates.io",
      "name" : "aws-smithy-http-server"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "0.66.5"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 0.66.4"
    }
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/smithy-lang/smithy-rs/security/advisories/GHSA-jvxp-qmx7-gjpx"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-16756"
  }, {
    "type" : "WEB",
    "url" : "https://aws.amazon.com/security/security-bulletins/2026-064-aws"
  }, {
    "type" : "WEB",
    "url" : "https://crates.io/crates/aws-smithy-http-server/0.66.5"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/smithy-lang/smithy-rs"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-770" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-07-24T22:37:39Z",
    "nvd_published_at" : "2026-07-23T19:16:53Z"
  }
}