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

unknownCVE-2026-15957

Bulletin ID: 2026-061-AWS Scope: AWS Content Type: Important (requires attention) Publication Date: 07/21/2026 12:45 PM PDT 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. We identified CVE-2026-15957, where uncontrolled recursion in the JSON, CBOR, and XML deserializer functions emitted by Amazon smithy-rs code generation could allow a third party 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. Impacted versions: aws-sdk-rust crates < release-2026-06-0 Please refer to the article below for the most up-to-date and complete information related to this AWS Security Bulletin.

CSIRTS triage

vendor: AWS product: smithy-rs Denial of serviceaffected: aws-sdk-rust crates < release-2026-06-0

What: Uncontrolled recursion in deserializer functions can lead to denial of service via stack exhaustion.
Who is affected: Deployments using affected versions of smithy-rs for JSON, CBOR, and XML deserialization are at risk.
Urgency: Immediate action is required to prevent potential denial of service attacks.
Action: Upgrade to the latest version of aws-sdk-rust to mitigate the vulnerability.

AI-assisted analysis generated from the source advisory — verify against the original.

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Details

Source: AWS Security Bulletins (INTL · vendor-psirt · site)
Severity: unknown
Published: 2026-07-21
Exploitation: Not in CISA KEV at last sync

Original advisory: https://aws.amazon.com/security/security-bulletins/rss/2026-061-aws/

Exploitation outlook

EPSS (FIRST.org) estimates each CVE’s probability of exploitation in the next 30 days — here is the CSIRTS.com read on those numbers.

Low exploitation riskCVE-2026-159570.42% 30-day exploitation probability — currently an unlikely target, but scores change as exploit code circulates. Riskier than 34% of all scored CVEs.

Referenced CVEs

CVE	CSIRTS overview	External
CVE-2026-15957	coverage & exploitation status	NVD · CVE.org

Same CVEs, other sources

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highCVE-2026-15957: Smithy-RS is a Rust code generation and runtime framework that generates HTTP clients and serv…nvd

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