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Cross-site scripting (XSS) in the dynamic file uploads

Moderate severity GitHub Reviewed Published Feb 20, 2024 in decidim/decidim • Updated Feb 20, 2024

Package

bundler decidim (RubyGems)

Affected versions

>= 0.27.0, < 0.27.5

Patched versions

0.27.5
bundler decidim-core (RubyGems)
>= 0.27.0, < 0.27.5
0.27.5

Description

Impact

The dynamic file upload feature is subject to potential XSS attach in case the attacker manages to modify the file names of the records being uploaded to the server.

This appears in sections where the user controls the file upload dialogs themselves and has the technical knowledge to change the file names through the dynamic upload endpoint. Therefore I believe it would require the attacker to control the whole session of the particular user but in any case, this needs to be fixed.

Successful exploit of this vulneratibility would require the user to have successfully uploaded a file blob to the server with a malicious file name and then have the possibility to direct the other user to the edit page of the record where the attachment is attached.

The users are able to craft the direct upload requests themselves controlling the file name that gets stored to the database as shown here:
https://github.com/rails/rails/blob/a967d355c6fee9ad9b8bd115d43bc8b0fc207e7e/activestorage/app/controllers/active_storage/direct_uploads_controller.rb#L14

The attacker is able to change the filename e.g. to <svg onload=alert('XSS')> if they know how to craft these requests themselves. And then enter the returned blob ID to the form inputs manually by modifying the edit page source.

Therefore, anywhere we display these strings, we should properly escape them.

Patches

PR #11612 fixes this problem both for 0.28.dev and 0.27.x.

Workarounds

Disable dynamic uploads for the instance, e.g. from proposals.

References

OWASP ASVS v4.0.3-5.1.3

Credits

This issue was discovered in City of Helsinki's security audit against Decidim 0.27 done during September 2023. The security audit was implemented by Deloitte Finland.

References

@andreslucena andreslucena published to decidim/decidim Feb 20, 2024
Published by the National Vulnerability Database Feb 20, 2024
Published to the GitHub Advisory Database Feb 20, 2024
Reviewed Feb 20, 2024
Last updated Feb 20, 2024

Severity

Moderate

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v3 base metrics

Attack vector
Network
Attack complexity
Low
Privileges required
Low
User interaction
Required
Scope
Unchanged
Confidentiality
High
Integrity
Low
Availability
None

CVSS v3 base metrics

Attack vector: More severe the more the remote (logically and physically) an attacker can be in order to exploit the vulnerability.
Attack complexity: More severe for the least complex attacks.
Privileges required: More severe if no privileges are required.
User interaction: More severe when no user interaction is required.
Scope: More severe when a scope change occurs, e.g. one vulnerable component impacts resources in components beyond its security scope.
Confidentiality: More severe when loss of data confidentiality is highest, measuring the level of data access available to an unauthorized user.
Integrity: More severe when loss of data integrity is the highest, measuring the consequence of data modification possible by an unauthorized user.
Availability: More severe when the loss of impacted component availability is highest.
CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:H/I:L/A:N

EPSS score

0.044%
(11th percentile)

Weaknesses

CVE ID

CVE-2023-51447

GHSA ID

GHSA-9w99-78rj-hmxq

Source code

Credits

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