How severe is CVE-2026-18140?

CVE-2026-18140 has a CVSS score of 7.5/10, rated HIGH. Immediate patching is strongly recommended.

Which packages are affected by CVE-2026-18140?

CVE-2026-18140 affects the following packages: aws-smithy-json (crates.io). Ecosystems affected: crates.io.

How do I fix CVE-2026-18140?

Update aws-smithy-json to 0.62.7 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-18140 is resolved across your whole dependency graph.

How do I detect CVE-2026-18140 in my crates.io dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for aws-smithy-json, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate CVE-2026-18140 if there is no patch (or I can't update yet)?

Do not deserialise data from untrusted sources: where the format allows it, restrict deserialisation to an explicit allowlist of expected types, and prefer a data-only format (JSON, Protobuf) over one that can reconstruct arbitrary objects until you can upgrade.

Is CVE-2026-18140 actively exploited in the wild?

No public exploit code has been indexed for CVE-2026-18140 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for CVE-2026-18140?

CVE-2026-18140 has an EPSS (Exploit Prediction Scoring System) score of 0.4%, placing it in the 36th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is CVE-2026-18140?

CVE-2026-18140 is classified as CWE-674 (CWE-674). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2026-18140 published, and has it been updated?

CVE-2026-18140 was published on October 2, 2026 and was last updated on October 2, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

🦀

🦀 crates.io

Not in CISA KEV

HIGH severity

CVE-2026-18140 — aws-smithy-json

HIGHFix: smithy-lang/smithy-rs#4685

CVE-2026-18140 is a high-severity (CVSS 7.5) CWE-674 vulnerability in aws-smithy-json. A fix is available for aws-smithy-json — see the affected versions and patch details below.

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

Published

Oct 2, 2026

Updated

Oct 2, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

None indexed

Exploitation data as of Oct 21, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

No confirmed exploitation observed yet

CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.

Exploitation and automatability from CISA’s SSVC triage for CVE-2026-18140.

EPSS Exploitation Probability

via FIRST.org ↗

0.4%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs36th percentile — riskier than 36% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

CVE-2026-18140 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.

Where this sits among everything scored

Of 394,415 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.

Real-World Exposure

1 pkg affected

🦀aws-smithy-json

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects crates.io packages — download data is not available via public APIs for these ecosystems.

Description

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

Affected Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
🦀crates.io	`aws-smithy-json`	all versions	0.62.7`cargo update -p aws-smithy-json --precise 0.62.7`

Affected Products

1 product · 1 configurations

Application

aws-smithy-jsonamazon

< 0.62.7

range

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for aws-smithy-json, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update aws-smithy-json to 0.62.7 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-18140 is resolved across your whole dependency graph.
Workarounds
Do not deserialise data from untrusted sources: where the format allows it, restrict deserialisation to an explicit allowlist of expected types, and prefer a data-only format (JSON, Protobuf) over one that can reconstruct arbitrary objects until you can upgrade.

Fixing This On Your OS

If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.

Red HatImportant

This flaw in the `aws-smithy-json` runtime crate allows a remote unauthenticated attacker to trigger a denial of service by sending a crafted HTTP request with deeply nested JSON. Red Hat products utilizing `smithy-rs` generated servers, such as components in Red Hat Enterprise Linux and Red Hat Trusted Artifact…

Workaround published by Red Hat

Restrict network access to services that process JSON input using the `aws-smithy-json` runtime. Configure firewalls to limit incoming connections to trusted sources, thereby reducing the exposure to remote unauthenticated denial of service attacks. If the service is reloaded or restarted, ensure firewall rules persist.

Source: Red Hat security advisory for CVE-2026-18140 (CC BY 4.0)

Product	Fixed in	Advisory
Red Hat Enterprise Linux 10	`goose-0:1.38.0-1.el10_2`	RHSA-2026:67593
Red Hat Enterprise Linux 9	`goose-0:1.38.0-1.el9_8`	RHSA-2026:67595
Logging Subsystem for Red Hat OpenShift 6.0	`openshift-logging/vector-rhel9:1791777198`	RHSA-2026:83013
Logging Subsystem for Red Hat OpenShift 6.2	`openshift-logging/vector-rhel9:1789050538`	RHSA-2026:68349
Logging Subsystem for Red Hat OpenShift 6.5	`openshift-logging/vector-rhel9:1789659541`	RHSA-2026:70870
Logging Subsystem for Red Hat OpenShift 6.6	`openshift-logging/vector-rhel9:1788439747`	RHSA-2026:66521
Red Hat Trusted Artifact Signer 1.4	`rhtas/tuffer-rhel9:1791809629`	RHSA-2026:83603

Frequently Asked Questions

### 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 unauthentica