Bedrock AgentCore Starter Toolkit: Unverified Ownership
CVE-2026-4269 is a high-severity unverified ownership vulnerability in Bedrock AgentCore Starter Toolkit from AWS, with a CVSS 3.1 base score of 7.5 out of 10. It can be exploited remotely over the network by an unauthenticated attacker, but only if a user takes part, for example by opening a link or file. The record lists version 0.1.13 as the first without the flaw, so updating Bedrock AgentCore Starter Toolkit to that release or later removes the exposure. There is no confirmed exploitation so far. EPSS estimates a 0.29% chance of exploitation within 30 days, which is low compared with other CVEs.
High severity with no evidence of exploitation so far.
What to do
- Update Bedrock AgentCore Starter Toolkit to 0.1.13 or a later version.
- Read the advisory on aws.amazon.com for workarounds and exact fixed builds.
- Until you can update, restrict network access to the affected service so it is not reachable from untrusted networks.
- Because the attack needs a user to take part, warn users about unexpected links and files related to this product until it is patched.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| AWS | Bedrock AgentCore Starter Toolkit | 0.1.0 up to, but not including, 0.1.13 | 0.1.13 |
Version data comes from the organisation that assigned the CVE. Confirm against the vendor advisory before deciding you are unaffected.
How the severity score breaks down
- Attack vector
- NetworkCan be exploited remotely over a network, including the internet.
- Attack complexity
- HighSuccess depends on conditions outside the attacker's control.
- Privileges required
- NoneNo account or login is needed.
- User interaction
- RequiredA user must take an action such as opening a file or link.
- Scope
- UnchangedImpact stays within the vulnerable component.
- Confidentiality
- HighAll data handled by the component can be read.
- Integrity
- HighData or code can be modified at will.
- Availability
- HighThe component can be taken down completely.
Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H. Scored by CNA.
| Scoring system | Score | Severity | Scored by |
|---|---|---|---|
| CVSS 4.0 | 5.8 | Medium | CNA |
| CVSS 3.1 | 7.5 | High | CNA |
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.
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: Unverified Ownership
The product does not properly verify that a critical resource is owned by the proper entity.
How developers prevent this class of flaw
- Very carefully manage the setting, management, and handling of privileges. Explicitly manage trust zones in the software.
- Consider following the principle of separation of privilege. Require multiple conditions to be met before permitting access to a system resource.
Timeline
- CVE record published.
- CISA published its SSVC assessment (exploitation: none, automatable: no, technical impact: total).
- Record last changed materially (score, affected products, status or references).
References
Patches and release notes
Other vulnerabilities in Bedrock AgentCore Starter Toolkit
- 9.0 Critical severity
Recent Unverified Ownership vulnerabilities
- 7.5 High severity
- 8.1 High severity
- 7.8 High severity
- 7.2 High severity
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