CVE-2026-4269 - Improper S3 ownership verification in Bedrock AgentCore Starter Toolkit

unknownCVE-2026-4269

Bulletin ID: 2026-008-AWS Scope: AWS Content Type: Important (requires attention) Publication Date: 2026/03/16 11:15 AM PDT Description: A missing S3 ownership verification in the Bedrock AgentCore Starter Toolkit before version v0.1.13 may allow a remote actor to inject code during the build process, leading to code execution in the AgentCore Runtime. Impacted versions: All versions of Bedrock AgentCore Starter Toolkit versions before v0.1.13. This issue only affects users of the Bedrock AgentCore Starter Toolkit before version v0.1.13 who build the Toolkit after September 24, 2025. Any users on a version >=v0.1.13, and any users on previous versions who built the toolkit before September 24, 2025 are not affected. 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: Bedrock AgentCore Starter Toolkit Remote code executionOtheraffected: before v0.1.13

What: Missing S3 ownership verification may allow a remote actor to inject code during the build process.
Who is affected: Users of Bedrock AgentCore Starter Toolkit versions before v0.1.13 who build the Toolkit after September 24, 2025.
Urgency: Remediation is critical to prevent code injection during the build process.
Action: Upgrade to Bedrock AgentCore Starter Toolkit version v0.1.13 or later.

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: 2026-06-05
Exploitation: Not in CISA KEV at last sync

Original advisory: https://aws.amazon.com/security/security-bulletins/rss/2026-008-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-2026-42690.24% 30-day exploitation probability — currently an unlikely target, but scores change as exploit code circulates. Riskier than 15% of all scored CVEs.

Referenced CVEs

CVE	CSIRTS overview	External
CVE-2026-4269	coverage & exploitation status	NVD · CVE.org

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