Auth bypass in Flarum
CVE-2023-22489
Flarum is a discussion platform for websites. If the first post of a discussion is permanently deleted but the discussion stays visible, any actor who can view the discussion is able to create a new reply via the REST API, no matter the reply permission or lock status. This includes users that don't have a validated email. Guests cannot successfully create a reply because the API will fail with a 500 error when the user ID 0 is inserted into the database. This happens because when the first post of a discussion is permanently deleted, the `first_post_id` attribute of the discussion becomes `null` which causes access control to be skipped for all new replies. Flarum automatically makes discussions with zero comments invisible so an additional condition for this vulnerability is that the discussion must have at least one approved reply so that `discussions.comment_count` is still above zero after the post deletion. This can open the discussion to uncontrolled spam or just unintentional replies if users still had their tab open before the vulnerable discussion was locked and then post a reply when they shouldn't be able to. In combination with the email notification settings, this could also be used as a way to send unsolicited emails. Versions between `v1.3.0` and `v1.6.3` are impacted. The vulnerability has been fixed and published as flarum/core v1.6.3. All communities running Flarum should upgrade as soon as possible. There are no known workarounds.
Vulnerability class: Broken Access Control
Published · last modified .
CVSS v3 metric
CVSS v3 base score 3.5 (Low). Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:N/I:L/A:N.
EPSS exploit prediction
EPSS: 0.006 (44.1th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 44th percentile — 44.1% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.006 · newest: 0.006 · change: 0.000
Affected products
- Flarum
- Flarum Framework — versions >= 1.3.0, < 1.6.3
Weakness classification (CWE)
References
- github.com/flarum/framework/security/advisories/GHSA-hph3-hv3c-7725 (Third Party Advisory, Mitigation)
- github.com/flarum/framework/commit/12f14112a0ecd1484d97330b82beb2a145919015 (Patch, Third Party Advisory)
- github.com/flarum/framework/releases/tag/v1.6.3 (Third Party Advisory, Release Notes)
Frequently asked questions
- What is CVE-2023-22489?
- CVE-2023-22489 is a low-severity vulnerability in Flarum, classified under Missing Authorization. CVSS score: 3.5/10. Published 2023-01-13.
- How severe is CVE-2023-22489?
- Low severity. CVSS v3 base score is 3.5 out of 10.