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Medium, CVSS 5.8amended

Improper S3 ownership verification in Bedrock AgentCore Starter Toolkit

CVE-2026-4269GHSA-xfhr-q72q-jcrj

What to do

Vendor fix available. Upgrade each affected package to the fixed version on its release line (bedrock-agentcore-starter-toolkit 0.1.13), redeploy, then verify what is actually installed.

This page has no inventory attached, so it cannot say whether you are affected. A vendor fix is not proof that your deployment is fixed.

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Affected packages

Sources

Severity and exploitation
Exploitation
No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.
CVSS 4.0
5.8 · CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:P/VC:N/VI:N/VA:N/SC:H/SI:H/SA:H · score source
EPSS
  • CVE-2026-4269: 0.26% estimated exploitation activity in the next 30 days; percentile 17.47 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.
Source description

As published by the source; long descriptions are shortened.

Summary An issue has been identified in the Bedrock AgentCore Starter Toolkit versions prior to v0.1.13 that may allow a remote actor to inject code during the build process, leading to code execution in the AgentCore Runtime. Impact A remote actor could inject code during the build process, leading to code execution in the AgentCore Runtime and a complete loss of confidentiality, integrity, and availability of the affected AgentCore resource. 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 date are not affected. Patches This issue has been addressed in version v0.1.13. AWS recommends upgrading to the latest version and ensuring any forked or derivative code is patched to incorporate…

Dates and revisions
Published by the source
Last modified by the source
Source last checked
  1. Revision 3 · amended ·

    Amended from ghsa record GHSA-xfhr-q72q-jcrj

  2. Revision 2 · amended ·

    Reviewed OSV alias/range/CVSS4 correction; package source scopes and original publication preserved. No customer finding resolved.

  3. Revision 1 · created ·

    Published from osv record GHSA-xfhr-q72q-jcrj

Agent brief

Preview the exact text before you copy it. Commands are read-only suggestions; review them before running anything.

# Patch Next advisory brief: CVE-2026-4269

Advisory: Improper S3 ownership verification in Bedrock AgentCore Starter Toolkit
IDs: CVE-2026-4269, GHSA-xfhr-q72q-jcrj
Record: https://patchnext.com/advisories/cve-2026-4269 (revision 3, source checked 26 Oct 2026, 13:37 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 5.8)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: bedrock-agentcore-starter-toolkit 0.1.13. A vendor fix does not mean a deployment is fixed.

## Affected components
- PyPI bedrock-agentcore-starter-toolkit: affected < 0.1.13; fixed in 0.1.13

## Suggested inspection (read-only)
- `python -m pip show bedrock-agentcore-starter-toolkit`: prints the installed version. Run with the environment that serves production active.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on bedrock-agentcore-starter-toolkit.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-xfhr-q72q-jcrj (OSV record GHSA-xfhr-q72q-jcrj lists affected ranges: PyPI bedrock-agentcore-starter-toolkit >=0 <0.1.13 (fixed))
- Verified: https://github.com/advisories/GHSA-xfhr-q72q-jcrj (GitHub-reviewed advisory GHSA-xfhr-q72q-jcrj lists affected ranges: PyPI bedrock-agentcore-starter-toolkit >=0 <0.1.13)

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