CVE-2026-18140: aws-smithy-json Denial of Service Vulnerability

HIGH
Advisory Identifier: GHSA-8ffr-xgwf-xj56
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CVSS 7.5
CWE-674
Published
Advisory Summary

CVE-2026-18140 is a HIGH (CVSS 7.5) denial of service vulnerability (CWE-674: Uncontrolled Recursion) affecting aws-smithy-json libraries in the crates.io ecosystem. The issue involves uncontrolled recursion in the aws-smithy-json unknown-key skip path allows unauthenticated remote denial of service in smithy-rs generated servers. Remediation is available by upgrading affected packages to version 0.62.7.

CVE-2026-18140 at a Glance

CVE Identifier CVE-2026-18140
GHSA Identifier GHSA-8ffr-xgwf-xj56
Severity HIGH
CVSS v3.1 Base Score 7.5
CWE Classification CWE-674: Uncontrolled Recursion
Affected Product aws-smithy-json
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-2026-18140

To remediate this vulnerability, upgrade all affected aws-smithy-json 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-json fixed: 0.62.7 
Upgrade aws-smithy-json to 0.62.7
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-json

How to Check if You Are Affected

To determine whether your application is affected by CVE-2026-18140, inspect your project dependencies for aws-smithy-json:

inspect dependencies for aws-smithy-json

Analyze the terminal output to locate any version of aws-smithy-json in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 0.62.7), 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-674: Uncontrolled Recursion, where the product does not properly control the amount of recursion that takes place, consuming excessive resources, such as allocated memory or the program stack. In aws-smithy-json, 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 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](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-2026-18140 Affected aws-smithy-json Versions

1 component(s)
Fixed Versions:
0.62.7
Product / Package Ecosystem Affected Versions Fixed Version
aws-smithy-json
 crates.io
< 0.62.7
0.62.7

References

aws-smithy-json Security Information SECURITY
https://aws.amazon.com/security/security-bulletins/2026-067-aws
crates.io/crates/aws-smithy-j... WEB
https://crates.io/crates/aws-smithy-json/0.62.7
aws-smithy-json Source Repository REPOSITORY
https://github.com/smithy-lang/smithy-rs
GitHub Advisory / Wiki ADVISORY
https://github.com/smithy-lang/smithy-rs/security/advisories/GHSA-8ffr-xgwf-xj56
NVD — CVE-2026-18140 NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-18140
aws-smithy-json Source Repository REPOSITORY
https://github.com/smithy-lang/smithy-rs/pull/4685
Security Fix Commit FIX COMMIT
https://github.com/smithy-lang/smithy-rs/commit/8f0882046c467981ba5b4fd91a10befa96bd262f

Frequently Asked Questions

What is CVE-2026-18140?
CVE-2026-18140 is a security vulnerability in aws-smithy-json involving Uncontrolled recursion in the aws-smithy-json unknown-key skip path allows unauthenticated remote denial of service in smithy-rs generated servers under CWE-674: Uncontrolled Recursion.
Which aws-smithy-json versions are affected?
Affected versions include releases prior to 0.62.7 across affected packages: aws-smithy-json.
What version fixes CVE-2026-18140?
Upgrading to 0.62.7 (or the latest patched release for your respective branch) resolves the vulnerability.
Is aws-smithy-json affected?
Yes, aws-smithy-json is affected in releases prior to 0.62.7. Upgrade your dependency to 0.62.7 or later.
What is the CVSS score of CVE-2026-18140?
CVE-2026-18140 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-2026-18140?
CVE-2026-18140 is classified under CWE-674: Uncontrolled Recursion (The product does not properly control the amount of recursion that takes place, consuming excessive resources, such as allocated memory or the program stack.).
How can I check crates.io dependencies for CVE-2026-18140?
Run the dependency tree command: 'inspect dependencies for aws-smithy-json'. 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-8ffr-xgwf-xj56",
  "modified" : "2026-10-02T22:44:52Z",
  "published" : "2026-10-02T22:44:52Z",
  "aliases" : [ "CVE-2026-18140" ],
  "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",
  "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 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.\n\n### Impact\nUncontrolled 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.\n\nImpacted versions: aws-smithy-json <= 0.62.6\n\n### Patches\nThis 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.\n\n### Workarounds\nThere are no workarounds besides updating to the patched version.\n\n### References\nIf you have any questions or comments about this advisory, AWS asks that you contact [AWS/Amazon] Security via their [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-json"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "0.62.7"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 0.62.6"
    }
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/smithy-lang/smithy-rs/security/advisories/GHSA-8ffr-xgwf-xj56"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-18140"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/smithy-lang/smithy-rs/pull/4685"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/smithy-lang/smithy-rs/commit/8f0882046c467981ba5b4fd91a10befa96bd262f"
  }, {
    "type" : "WEB",
    "url" : "https://aws.amazon.com/security/security-bulletins/2026-067-aws"
  }, {
    "type" : "WEB",
    "url" : "https://crates.io/crates/aws-smithy-json/0.62.7"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/smithy-lang/smithy-rs"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-674" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-10-02T22:44:52Z",
    "nvd_published_at" : "2026-07-30T19:17:26Z"
  }
}