CVE-2026-29186
Description
A flaw was found in Backstage. The backstage/plugin-techdocs-node package uses an allowlist to filter dangerous MkDocs configuration keys during the documentation build process. A gap in this allowlist allows attackers to craft an mkdocs.yml file that causes arbitrary Python code execution.
Statement
To exploit this issue, an attacker needs commit access to a repository that Backstage is configured to track and build in order to introduce a malicious mkdocs.yml file into the TechDocs build pipeline. Additionally, an attacker can execute arbitrary Python code but the payload is confined by the permissions granted to the TechDocs build process which is typically a restricted service account, limiting the impact of this vulnerability. Due to these reasons, this vulnerability has been rated with an important severity.
Mitigation
To mitigate this issue, enable docker isolation by updating the Backstage configuration to use 'runIn: docker' instead of 'runIn: local', confining the arbitrary Python code execution to a containerized environment. Additionally, limit commit access to repositories tracked by Backstage to trusted contributors only, and enforce mandatory pull request (PR) reviews for any modifications made to the mkdocs.yml file.
Common Vulnerability Scoring System (CVSS) Score Details
Info alert:Important note
CVSS scores for open source components depend on vendor-specific factors (e.g. version or build chain). Therefore, Red Hat's score and impact rating can be different from NVD and other vendors. Red Hat remains the authoritative CVE Naming Authority (CNA) source for its products and services (see Red Hat classifications).
CVSS v3 Score Breakdown
| Red Hat | NVD | cve.org | |
|---|---|---|---|
| Base Score | 9.1 | 9.8 | 9.1 |
| Attack Vector | Network | Network | Network |
| Attack Complexity | Low | Low | Low |
| Privileges Required | Low | None | Low |
| User Interaction | None | None | None |
| Scope | Changed | Unchanged | Changed |
| Confidentiality | High | High | High |
| Integrity Impact | Low | High | Low |
| Availability Impact | Low | High | Low |
Vector
Red Hat: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:L/A:L
NVD: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
cve.org: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:L/A:L
Understanding the Weakness (CWE)
Integrity
Technical Impact: Unexpected State
Frequently Asked Questions
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