# Improper S3 ownership verification in Bedrock AgentCore Starter Toolkit

Advisory record · `GHSA-xfhr-q72q-jcrj`

- **Identifiers:** `GHSA-xfhr-q72q-jcrj` · `CVE-2026-4269` · `PYSEC-2026-2396`
- **State:** Confirmed
- **Severity:** CVSS 5.8 Medium
- **Critical:** No
- **Weakness (CWE):** [CWE-283](https://cwe.mitre.org/data/definitions/283.html) · [CWE-340](https://cwe.mitre.org/data/definitions/340.html)
- **Tags:** [CWE-283](https://agentprime.io/advisories/tag/cwe-283.md) · [CWE-340](https://agentprime.io/advisories/tag/cwe-340.md)
- **Published:** 17 Mar 2026
- **Updated:** 13 Jul 2026
- **Reviewed by a person:** No

Published by the GitHub Advisory Database at 17 Mar 2026, 20:34 UTC. agentprime has not analysed this yet, so whether it affects any app is not known.

## Affected packages

- `bedrock-agentcore-starter-toolkit` (PyPI): affected `<0.1.13`; fixed in `0.1.13`

## Not analysed yet

We haven’t published our analysis of this Advisory yet. Once a person has reviewed it, this page will say what’s vulnerable, what has to be true for your app to be affected, and how to check.

## Severity and exploitation

- 5.8 Medium, CVSS 4.0: `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`, from CNA (AMZN)

- **CISA KEV:** Not listed.
- **EPSS:** 0.0026, the 17th percentile, on 5 Nov 2026: FIRST’s estimate of the chance of exploitation in the next 30 days.

## Timeline

- 31 Oct 2026, 15:01 UTC: First seen by agentprime
- 31 Oct 2026, 15:01 UTC: [Confirmed by OSV](https://osv.dev/vulnerability/GHSA-xfhr-q72q-jcrj)

## Sources

- [GitHub Advisory Database: GHSA-xfhr-q72q-jcrj](https://github.com/advisories/GHSA-xfhr-q72q-jcrj)
- [OSV: GHSA-xfhr-q72q-jcrj](https://osv.dev/vulnerability/GHSA-xfhr-q72q-jcrj)
- <https://github.com/aws/bedrock-agentcore-starter-toolkit/security/advisories/GHSA-xfhr-q72q-jcrj>
- <https://nvd.nist.gov/vuln/detail/CVE-2026-4269>
- <https://aws.amazon.com/security/security-bulletins/2026-008-AWS>
- <https://github.com/aws/bedrock-agentcore-starter-toolkit>
- <https://github.com/aws/bedrock-agentcore-starter-toolkit/releases/tag/v0.1.13>

Facts on this page come from the GitHub Advisory Database (CC-BY 4.0), OSV and the other sources listed, as published. We don’t reproduce full advisory descriptions, which can contain exploit code.

## Check whether this affects you

A Match means an installed version is in the affected range above. Most don’t affect the app; agentprime hasn’t analysed this one yet.

- With the agentprime MCP server (<https://api.agentprime.io/mcp>), ask your agent to check the project: `check_lockfile` sends a lockfile, `check_packages` a list of installed packages, and both return the Matches and the upgrades that clear them. `get_advisory` returns this record. Setup: <https://agentprime.io/mcp.md>
- In a browser: <https://agentprime.io/check/> reads your lockfile in the browser, never uploading it.
- Whether it touches your code, with file and line: the Claude Code plugin, <https://agentprime.io/plugin.md>
- As JSON: <https://api.agentprime.io/v1/advisories/GHSA-xfhr-q72q-jcrj>, or `POST https://api.agentprime.io/v1/match` with your packages (<https://agentprime.io/api.md>)

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The web page: <https://agentprime.io/advisories/GHSA-xfhr-q72q-jcrj/>. Everything for agents: <https://agentprime.io/llms.txt>.