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

> Remote attackers can inject code during the build process of the Bedrock AgentCore Starter Toolkit, leading to code execution in the runtime.

- **Severity:** Medium 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`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** A user has to click or open something
- **Fix available:** Yes
- **Published:** 16 Mar 2026
- **Updated:** 16 Mar 2026
- **Also known as:** GHSA-xfhr-q72q-jcrj, PYSEC-2026-2396

## What is CVE-2026-4269?

CVE-2026-4269 is a medium-severity vulnerability in AWS Bedrock AgentCore Starter Toolkit, published on 16 Mar 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.

### Official 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.

Weakness: CWE-340 (Generation of Predictable Numbers or Identifiers), CWE-283 (Unverified Ownership)

## Which versions are affected by CVE-2026-4269?

3 open source packages ship an affected version, including bedrock-agentcore-starter-toolkit. It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `bedrock-agentcore-starter-toolkit` | PyPI | All versions | 0.1.13 |
| `bedrock-agentcore-starter-toolkit` | PyPI | All versions | 0.1.13 |
| `bedrock-agentcore-starter-toolkit` | PyPI | All versions | 0.1.13 |

Products: Amazon Bedrock Agentcore Starter Toolkit.

## How do I fix CVE-2026-4269?

Upgrade bedrock-agentcore-starter-toolkit to 0.1.13 or later.

## Is CVE-2026-4269 being exploited?

There is no known exploitation of CVE-2026-4269 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-4269 and fix it if it is affected.

What it is: CVE-2026-4269 is a medium-severity vulnerability in AWS Bedrock AgentCore Starter Toolkit, published on 16 Mar 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Exploitation: There is no known exploitation of CVE-2026-4269 in the wild and no public exploit code.

Affected packages and fixed versions:
- bedrock-agentcore-starter-toolkit (PyPI): affected all versions; fixed in 0.1.13
- bedrock-agentcore-starter-toolkit (PyPI): affected all versions; fixed in 0.1.13
- bedrock-agentcore-starter-toolkit (PyPI): affected all versions; fixed in 0.1.13

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-4269/ (Markdown: https://insights.sbomify.com/CVE-2026-4269/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-4269
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-4269
- OSV: https://osv.dev/vulnerability/CVE-2026-4269

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-4269/
Summaries are generated and may contain mistakes; the official description above is the record.