# 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

Advisory record · `GHSA-8ffr-xgwf-xj56`

- **Identifiers:** `GHSA-8ffr-xgwf-xj56` · `CVE-2026-18140`
- **State:** Confirmed
- **Severity:** CVSS 8.7 High
- **Critical:** No
- **Weakness (CWE):** [CWE-674](https://cwe.mitre.org/data/definitions/674.html)
- **Tags:** [Denial of service](https://agentprime.io/advisories/tag/dos.md)
- **Published:** 2 Oct 2026
- **Updated:** 2 Oct 2026
- **Reviewed by a person:** No

Published by the GitHub Advisory Database at 2 Oct 2026, 22:44 UTC. agentprime has not analysed this yet, so whether it affects any app is not known.

## Affected packages

- `aws-smithy-json` (crates.io): affected `<0.62.7`; fixed in `0.62.7`

## Machine-written summary

Summary written by Claude Haiku from the source advisory. Not reviewed by a person.

> The aws-smithy-json crate, versions before 0.62.7, has uncontrolled recursion in its unknown-key skip path. An unauthenticated remote attacker can send a single small HTTP request containing deeply nested JSON to a server generated by smithy-rs, causing stack exhaustion and a process abort. Upgrade aws-smithy-json to version 0.62.7 or later. No workarounds are listed.

Written 3 Nov 2026.

## Not analysed yet

We haven’t published our analysis of this Advisory yet. Once a person has reviewed it, this page will say what’s vulnerable, what has to be true for your app to be affected, and how to check.

## Severity and exploitation

- 8.7 High, CVSS 4.0: `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`, from CNA (AMZN)

- **CISA KEV:** Not listed.
- **EPSS:** 0.0078, the 56th percentile, on 6 Nov 2026: FIRST’s estimate of the chance of exploitation in the next 30 days.

## Timeline

- 31 Oct 2026, 14:24 UTC: First seen by agentprime
- 31 Oct 2026, 14:24 UTC: [Confirmed by OSV](https://osv.dev/vulnerability/GHSA-8ffr-xgwf-xj56)

## Sources

- [GitHub Advisory Database: GHSA-8ffr-xgwf-xj56](https://github.com/advisories/GHSA-8ffr-xgwf-xj56)
- [OSV: GHSA-8ffr-xgwf-xj56](https://osv.dev/vulnerability/GHSA-8ffr-xgwf-xj56)
- <https://github.com/smithy-lang/smithy-rs/security/advisories/GHSA-8ffr-xgwf-xj56>
- <https://nvd.nist.gov/vuln/detail/CVE-2026-18140>
- <https://github.com/smithy-lang/smithy-rs/pull/4685>
- <https://github.com/smithy-lang/smithy-rs/commit/8f0882046c467981ba5b4fd91a10befa96bd262f>
- <https://aws.amazon.com/security/security-bulletins/2026-067-aws>
- <https://crates.io/crates/aws-smithy-json/0.62.7>
- <https://github.com/smithy-lang/smithy-rs>

Facts on this page come from the GitHub Advisory Database (CC-BY 4.0), OSV and the other sources listed, as published. We don’t reproduce full advisory descriptions, which can contain exploit code.

## Check whether this affects you

A Match means an installed version is in the affected range above. Most don’t affect the app; agentprime hasn’t analysed this one yet.

- With the agentprime MCP server (<https://api.agentprime.io/mcp>), ask your agent to check the project: `check_lockfile` sends a lockfile, `check_packages` a list of installed packages, and both return the Matches and the upgrades that clear them. `get_advisory` returns this record. Setup: <https://agentprime.io/mcp.md>
- In a browser: <https://agentprime.io/check/> reads your lockfile in the browser, never uploading it.
- Whether it touches your code, with file and line: the Claude Code plugin, <https://agentprime.io/plugin.md>
- As JSON: <https://api.agentprime.io/v1/advisories/GHSA-8ffr-xgwf-xj56>, or `POST https://api.agentprime.io/v1/match` with your packages (<https://agentprime.io/api.md>)

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The web page: <https://agentprime.io/advisories/GHSA-8ffr-xgwf-xj56/>. Everything for agents: <https://agentprime.io/llms.txt>.