GHSA-hph3-hv3c-7725
LOWAny Flarum user including unactivated can reply in public discussions whose first post was permanently deleted
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
Blast Radius
flarum/coreReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects Packagist packages — download data is not available via public APIs for these ecosystems.
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.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐘Packagist | flarum/core | ≥ 1.3.0&&< 1.6.3 | 1.6.3 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for flarum/core. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update flarum/core to 1.6.3 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-hph3-hv3c-7725 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 pinpoints whether GHSA-hph3-hv3c-7725 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to GHSA-hph3-hv3c-7725. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is GHSA-hph3-hv3c-7725 in your dependencies?
O3 detects GHSA-hph3-hv3c-7725 across Packagist dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.