CVE-2023-22487 Post mentions can be used to read any post on the forum without access control

High 7.7 Published 11 Jan 2023 Updated 10 Mar 2025

Attackers can read private or restricted forum posts by mentioning their IDs, bypassing access controls in the mentions extension.

Exploited in the wild: Not known
Login needed: Any signed-in user
Attackable: Over the internet
Victim action needed: Not needed
Fix: Available

What is CVE-2023-22487?

CVE-2023-22487 is a high-severity missing authorization vulnerability in flarum framework, published on 11 Jan 2023. Any signed-in user can exploit it over the network, with no action from the victim.

Official description

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.

Weakness: CWE-284

Which versions are affected by CVE-2023-22487?

2 open source packages ship an affected version, including flarum/mentions. It affects 1 product.

Package	Affected	Fixed in
`flarum/mentions` Packagist	All versions	`1.6.3`
`flarum/mentions` Packagist	All versions	`1.6.3`

Products include Flarum Flarum.

How do I fix CVE-2023-22487?

Upgrade flarum/mentions to 1.6.3 or later.

Upgrade, and check permissions on every request on the server, not only in the interface. More about Missing authorization.

Is CVE-2023-22487 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2023-22487 exists.

Sources

Also known as GHSA-22m9-m3ww-53h3.