Skip to content

Any user including unactivated can reply in public discussions whose first post was permanently deleted

Low
SychO9 published GHSA-hph3-hv3c-7725 Jan 10, 2023

Package

composer flarum/core (Composer)

Affected versions

< 1.3.0

Patched versions

1.6.3

Description

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 should also be fixed to return the expected 401/403 status.

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.

Impact

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.

Patches

The vulnerability has been fixed and published as flarum/core v1.6.3. All communities running Flarum should upgrade as soon as possible to v1.6.3 using:

composer update --prefer-dist --no-dev -a -W

You can then confirm you run the latest version using:

composer show flarum/core

Workarounds

If you don't delete the first posts you are not affected. A workaround can be to delete the discussion itself, or amend the database to manually set a first_post_id.

For more information

For any questions or comments on this vulnerability please visit https://discuss.flarum.org/

For support questions create a discussion at https://discuss.flarum.org/t/support.

A reminder that if you ever become aware of a security issue in Flarum, please report it to us privately by emailing [email protected], and we will address it promptly.

Severity

Low

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v3 base metrics

Attack vector
Network
Attack complexity
Low
Privileges required
Low
User interaction
Required
Scope
Unchanged
Confidentiality
None
Integrity
Low
Availability
None

CVSS v3 base metrics

Attack vector: More severe the more the remote (logically and physically) an attacker can be in order to exploit the vulnerability.
Attack complexity: More severe for the least complex attacks.
Privileges required: More severe if no privileges are required.
User interaction: More severe when no user interaction is required.
Scope: More severe when a scope change occurs, e.g. one vulnerable component impacts resources in components beyond its security scope.
Confidentiality: More severe when loss of data confidentiality is highest, measuring the level of data access available to an unauthorized user.
Integrity: More severe when loss of data integrity is the highest, measuring the consequence of data modification possible by an unauthorized user.
Availability: More severe when the loss of impacted component availability is highest.
CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:N/I:L/A:N

CVE ID

CVE-2023-22489

Weaknesses

Credits