CVE-2023-22487: Flarum is a forum software for building communities. Using the mentions feature provided by the flarum/mentions extension, users can mention any post ...

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.

Metrics

CVSS 3.1

4.3/10

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N

EPSS Probability

0.66%

47.1th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

CWE-284

Affected Software

Vendor	Product	Versions
Flarum	Flarum	< 1.6.3

References

https://github.com/flarum/framework/commit/ab1c868b978e8b0d09a5d682c54665dae17d0985Patch, Third Party Advisory
https://github.com/flarum/framework/security/advisories/GHSA-22m9-m3ww-53h3Exploit, Mitigation, Third Party Advisory
https://github.com/flarum/framework/commit/ab1c868b978e8b0d09a5d682c54665dae17d0985Patch, Third Party Advisory
https://github.com/flarum/framework/security/advisories/GHSA-22m9-m3ww-53h3Exploit, Mitigation, Third Party Advisory

Timeline

Published: Jan 11, 2023
Last Modified: Jun 17, 2026
Status: Modified

Frequently Asked Questions

What is CVE-2023-22487?

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.

How severe is CVE-2023-22487?

CVE-2023-22487 has a CVSS score of 4.3/10 (MEDIUM severity). The EPSS model estimates a 0.66% probability of exploitation in the next 30 days.

How do I fix CVE-2023-22487?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.