CVE-2023-22487

What it is

Flarum is a forum software for building communities. Using the mentions feature provided by the flarum/mentions extension, users can mention any post ID on the forum with the special `@"<username>"#p<id>` syntax. The following behavior never changes no matter if the actor should be able to read the mentioned post or not: A URL to the mentioned post is inserted into the actor post HTML, leaking its discussion ID and post number. The `mentionsPosts` relationship included in the `POST /api/posts` and `PATCH /api/posts/<id>` JSON responses leaks the full JSON:API payload of all mentioned posts without any access control. This includes the content, date, number and attributes added by other extensions. An attacker only needs the ability to create new posts on the forum to exploit the vulnerability. This works even if new posts require approval. If they have the ability to edit posts, the attack can be performed even more discreetly by using a single post to scan any size of database and hiding the attack post content afterward. The attack allows the leaking of all posts in the forum database, including posts awaiting approval, posts in tags the user has no access to, and private discussions created by other extensions like FriendsOfFlarum Byobu. This also includes non-comment posts like tag changes or renaming events. The discussion payload is not leaked but using the mention HTML payload it's possible to extract the discussion ID of all posts and combine all posts back together into their original discussions even if the discussion title remains unknown. All Flarum versions prior to 1.6.3 are affected. The vulnerability has been fixed and published as flarum/core v1.6.3. As a workaround, user can disable the mentions extension.

At a glance

Exploitability

Can be exploited over the network with a low-privilege account. High risk of data exposure.

Exploit odds

0.7% chance of exploitation in the next 30 days (EPSS).

Fix

A patch, advisory or fixed version is referenced. Upgrade or apply it.

Timeline

1. 2023-01-11 20:15 UTC PublishedDisclosed publicly on CVE.org and NVD
2. 2026-06-17 05:35 UTC Last updatedMost recent change to the record

Why it ranks here

• Exploited in the wild: no, CISA does not list it.
• Exploit odds: 0.7% in the next 30 days (EPSS).
• Severity: 7.7 HIGH (CVSS).
• Fix: a patch or advisory is linked.

Details

Published

2023-01-11 20:15 UTC

Last modified

2026-06-17 05:35 UTC

Exploit probability

0.7% · EPSS, next 30 days

Weakness

CWE-284 · Improper access control

Record status

Modified

Affected

• Flarum < 1.6.3

Attack profile CVSS 3.1 · 7.7

Attack vector

Network

Complexity

Low

Privileges needed

Low

User interaction

None

Scope

Changed

Confidentiality

High

Integrity

None

Availability

None

Is it in your code?

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