CVE-2026-47657: HumHub Authorization Bypass Vulnerability

CVE-2026-47657 Overview

CVE-2026-47657 is a missing authorization vulnerability in HumHub, an open source enterprise social network platform. Versions 1.13.0 through 1.18.2 fail to validate user permissions in the Space member management controller. Any authenticated user can trigger the removal of all members from any Space, regardless of their role or membership status. The flaw maps to [CWE-862: Missing Authorization]. HumHub released version 1.18.3 to address the issue.

Critical Impact
Any authenticated user can wipe the entire membership of any Space in the HumHub instance, causing loss of collaboration state and disrupting organizational communication.

Affected Products

HumHub versions 1.13.0 through 1.18.2
HumHub Open Source Enterprise Social Network
Self-hosted HumHub deployments across all editions in the affected version range

Discovery Timeline

2026-07-21 - CVE-2026-47657 published to the National Vulnerability Database (NVD)
2026-07-23 - Last updated in NVD database

Technical Details for CVE-2026-47657

Vulnerability Analysis

The vulnerability resides in the Space member management controller within HumHub. This controller exposes an action that removes all members from a target Space. The controller does not verify whether the requesting user holds administrative permissions over the Space, nor does it verify Space membership. An authenticated user with the lowest privilege level can invoke the endpoint and clear every member from any Space in the instance.

The impact is scoped to integrity of Space membership data. Confidentiality and availability of the underlying HumHub instance remain intact, but affected Spaces lose their collaboration state until administrators restore membership manually or from backups.

Root Cause

The root cause is a missing authorization check ([CWE-862]) in the controller action responsible for bulk member removal. Standard HumHub controllers enforce Space-level role checks such as owner or administrator before performing destructive operations. The affected action omitted this check, treating authentication alone as sufficient authorization. The upstream fix in pull request #8163 adds the missing access control validation before executing the removal logic.

Attack Vector

Exploitation requires network access to the HumHub web interface and a valid authenticated session. No user interaction from the victim is required. An attacker with any low-privileged account crafts a request to the vulnerable member management endpoint, supplying the target Space identifier. The controller processes the request and removes every member from the specified Space. Attackers can iterate across Space identifiers to disrupt multiple Spaces in sequence.

No verified public exploit code is available. Refer to the HumHub Security Advisory GHSA-hj67-5q6h-j7c2 for authoritative technical details.

Detection Methods for CVE-2026-47657

Indicators of Compromise

Unexpected bulk removal events in HumHub Space membership logs affecting multiple or all members simultaneously
Space membership audit entries showing member removals initiated by user accounts without administrative privileges on the target Space
User complaints reporting sudden loss of access to Spaces they were previously members of

Detection Strategies

Review HumHub application and database logs for Space member deletion events grouped by short time windows and correlate the acting user against the Space's administrator list
Query the space_membership audit trail for removal operations where the initiating user is not the Space owner or administrator
Enable verbose logging on the Space member management controller to capture request source IP, session identifier, and target Space ID

Monitoring Recommendations

Alert on any request to Space member management endpoints that removes more than a threshold number of members in a single operation
Monitor web server access logs for repeated POST requests to member management URLs originating from a single authenticated session
Track anomalous drops in Space membership counts across the platform and correlate with the acting user account

How to Mitigate CVE-2026-47657

Immediate Actions Required

Upgrade HumHub to version 1.18.3 or later without delay, as this release contains the authorization fix
Audit recent Space membership changes across all Spaces to identify unauthorized bulk removals that may predate the upgrade
Restrict network access to the HumHub instance to trusted users until the patch is applied

Patch Information

The vulnerability is fixed in HumHub version 1.18.3. The upstream fix was merged via HumHub Pull Request #8163, which adds the missing authorization check to the Space member management controller. Administrators should follow the standard HumHub upgrade procedure and verify the running version after deployment. See the HumHub Security Advisory GHSA-hj67-5q6h-j7c2 for the vendor's guidance.

Workarounds

No known workaround is available according to the vendor advisory; upgrading to 1.18.3 or later is the only supported remediation
Where immediate upgrade is not possible, limit account creation and reduce the population of authenticated users to minimize the attacker pool
Maintain frequent backups of Space membership data to allow rapid restoration if bulk removal occurs

bash

# Upgrade HumHub to the patched release
cd /path/to/humhub
git fetch --tags
git checkout v1.18.3
php protected/yii migrate/up --includeModuleMigrations=1