backstage: Unrestricted Upload of File with Dangerous Type
CVE-2026-29186 is a critical-severity unrestricted upload of file with dangerous type vulnerability in backstage, with a CVSS 3.1 base score of 9.8 out of 10. It can be exploited remotely over the network by an unauthenticated attacker, without any action from a user. Affected backstage versions: < 1.14.3. The record does not name a fixed version, so check the vendor advisory. There is no confirmed exploitation so far. EPSS estimates a 0.87% chance of exploitation within 30 days, higher than 59% of scored CVEs.
Critical severity: a successful attack would have severe impact.
What to do
- Update Backstage Plugin-techdocs-node to 1.14.3 or a later version.
- Read the advisory on github.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.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Backstage | backstage | < 1.14.3 | Not stated |
| Red Hat | Red Hat Developer Hub 1.8 | Not specified in the record | Not stated |
| Red Hat | Red Hat Developer Hub 1.9 | Not specified in the record | Not stated |
| Red Hat | Self-service automation portal 2 | Not specified in the record | Not stated |
| Linux Foundation | Backstage Plugin-techdocs-node | before 1.14.3 | 1.14.3 |
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
- LowNo special conditions are needed; the attack works reliably.
- Privileges required
- NoneNo account or login is needed.
- User interaction
- NoneNo action by a victim is required.
- 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:L/PR:N/UI:N/S:U/C:H/I:H/A:H. Scored by NVD.
| Scoring system | Score | Severity | Scored by |
|---|---|---|---|
| CVSS 3.1 | 7.7 | High | CNA (github.com) |
| CVSS 3.1 | 9.8 | Critical | NVD |
| CVSS 3.1 | 9.1 | Critical | CNA |
Official description
Backstage is an open framework for building developer portals. Prior to version 1.14.3, this is a configuration bypass vulnerability that enables arbitrary code execution. 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 that causes arbitrary Python code execution, completely bypassing TechDocs' security controls. This issue has been patched in version 1.14.3.
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: Unrestricted Upload of File with Dangerous Type
The product allows the upload or transfer of dangerous file types that are automatically processed within its environment.
How developers prevent this class of flaw
- Generate a new, unique filename for an uploaded file instead of using the user-supplied filename, so that no external input is used at all.
- When the set of acceptable objects, such as filenames or URLs, is limited or known, create a mapping from a set of fixed input values (such as numeric IDs) to the actual filenames or URLs, and reject all other inputs.
- Consider storing the uploaded files outside of the web document root entirely. Then, use other mechanisms to deliver the files dynamically.
More Unrestricted Upload of File with Dangerous Type vulnerabilities (CWE-434)
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
Other references
Other vulnerabilities in backstage
- 7.7 High severity
- 8.8 High severity
- 7.7 High severity
- 7.7 High severity
- 8.8 High severity
- 8.5 High severity
Recent Unrestricted Upload of File with Dangerous Type vulnerabilities
- 9.8 Critical severity
- 8.8 High severity
- 8.8 High severity
- 8.1 High severity
- 8.5 High severity
- 9.1 Critical severity
Spotted an error? Tell us.