CVE-2021-21283 Detail

Current Description

Flarum is an open source discussion platform for websites. The "Flarum Sticky" extension versions 0.1.0-beta.14 and 0.1.0-beta.15 has a cross-site scripting vulnerability. A change in release beta 14 of the Sticky extension caused the plain text content of the first post of a pinned discussion to be injected as HTML on the discussion list. The issue was discovered following an internal audit. Any HTML would be injected through the m.trust() helper. This resulted in an HTML injection where <script> tags would not be executed. However it was possible to run javascript from other HTML attributes, enabling a cross-site scripting (XSS) attack to be performed. Since the exploit only happens with the first post of a pinned discussion, an attacker would need the ability to pin their own discussion, or be able to edit a discussion that was previously pinned. On forums where all pinned posts are authored by your staff, you can be relatively certain the vulnerability has not been exploited. Forums where some user-created discussions were pinned can look at the first post edit date to find whether the vulnerability might have been exploited. Because Flarum doesn't store the post content history, you cannot be certain if a malicious edit was reverted. The fix will be available in version v0.1.0-beta.16 with Flarum beta 16. The fix has already been back-ported to Flarum beta 15 as version v0.1.0-beta.15.1 of the Sticky extension. Forum administrators can disable the Sticky extension until they are able to apply the update. The vulnerability cannot be exploited while the extension is disabled.


View Analysis Description

Severity



CVSS 3.x Severity and Metrics:

NIST CVSS score matches with CNA score
CNA:  GitHub, Inc.
Base Score:  5.4 MEDIUM
Vector:  CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N


NVD Analysts use publicly available information to associate vector strings and CVSS scores. We also display any CVSS information provided within the CVE List from the CNA.

Note: The NVD and the CNA have provided the same score. When this occurs only the CNA information is displayed, but the Acceptance Level icon for the CNA is given a checkmark to signify NVD concurrence.

References to Advisories, Solutions, and Tools

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Hyperlink Resource
https://discuss.flarum.org/d/26042-security-update-to-flarum-sticky-010-beta151) Mitigation  Vendor Advisory 
https://github.com/flarum/sticky/commit/7ebd30462bd405c4c0570b93a6d48710e6c3db19 Patch  Third Party Advisory 
https://github.com/flarum/sticky/pull/24 Patch  Third Party Advisory 
https://github.com/flarum/sticky/security/advisories/GHSA-h3gg-7wx2-cq3h Third Party Advisory 

Weakness Enumeration

CWE-ID CWE Name Source
CWE-79 Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') Provider acceptance level GitHub, Inc.  

Known Affected Software Configurations Switch to CPE 2.2

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Change History

1 change records found show changes

Quick Info

CVE Dictionary Entry:
CVE-2021-21283
NVD Published Date:
01/26/2021
NVD Last Modified:
02/04/2021
Source:
GitHub, Inc.