CVE-2026-4269 — bedrock-agentcore-starter…
CVE-2026-4269 is a CWE-283 vulnerability in bedrock-agentcore-starter-toolkit. A fix is available for bedrock-agentcore-starter-toolkit — see the affected versions and patch details below.
Improper S3 ownership verification in Bedrock AgentCore Starter Toolkit
Exploitation Status
No confirmed exploitation observed yet
- A successful exploit gives an attacker total control of the affected component, not partial access.
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for CVE-2026-4269.
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
Real-World Exposure
bedrock-agentcore-starter-toolkitReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects PyPI packages — download data is not available via public APIs for these ecosystems.
Description
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 the new fixes.
Workarounds
N/A
References
If you have any questions or comments about this advisory, contact [AWS/Amazon] Security via our vulnerability reporting page or directly via email to [email protected]. Please do not create a public GitHub issue.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐍PyPI | bedrock-agentcore-starter-toolkit | all versions | 0.1.13pip install --upgrade 'bedrock-agentcore-starter-toolkit==0.1.13' |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for bedrock-agentcore-starter-toolkit, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update bedrock-agentcore-starter-toolkit to 0.1.13 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-4269 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2026-4269 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2026-4269. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2026-4269 in your dependencies?
O3 Security finds CVE-2026-4269 across PyPI dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.