CVE-2026-61399 Overview
CVE-2026-61399 is an Improper Encoding or Escaping of Output vulnerability [CWE-116] in the Apache CloudStack user interface. The flaw resides in the Lock User functionality, where user-controlled input is rendered without adequate output encoding. An authenticated attacker with high privileges can inject content that executes in another administrator's browser session when the Lock User feature is used. The Apache CloudStack project has released fixed versions to address the flaw.
Critical Impact
Authenticated administrators can inject unescaped output that executes in privileged browser sessions, enabling limited confidentiality and integrity impact with a scope change across the CloudStack management UI.
Affected Products
- Apache CloudStack versions 4.20.0.0 through 4.20.3.0
- Apache CloudStack versions 4.21.0.0 through 4.22.1.0
- Fixed in Apache CloudStack 4.20.3.1 and 4.22.1.1
Discovery Timeline
- 2026-08-21 - CVE-2026-61399 published to NVD
- 2026-08-27 - Last updated in NVD database
Technical Details for CVE-2026-61399
Vulnerability Analysis
The vulnerability originates in the Apache CloudStack management UI when administrators invoke the Lock User functionality. User-supplied fields associated with a locked account are returned to the browser without proper HTML or JavaScript context encoding. When those fields are rendered in the UI, embedded markup or script content is interpreted by the browser instead of displayed as text.
Exploitation requires an authenticated attacker with high privileges and user interaction from a victim administrator. Because the scope changes from the vulnerable component to the surrounding UI, injected payloads can influence other portions of the CloudStack console. Successful exploitation grants attackers a limited ability to read and modify data accessible through the victim's session, including virtual machine, network, and account operations exposed by the CloudStack API.
Root Cause
The root cause is an output encoding defect [CWE-116]. Data associated with the Lock User workflow is written into the UI response without context-aware escaping, allowing attacker-controlled strings to break out of their intended textual context and execute as markup or script.
Attack Vector
The attack vector is network-based over the CloudStack management UI. An attacker who already holds a privileged CloudStack account seeds malicious content into a user record. When another administrator triggers the Lock User workflow and views the affected record, the payload executes in the victim's authenticated session. Refer to the Apache Mailing List Thread for the vendor advisory.
No public proof-of-concept exploit is available at this time. The EPSS probability is 0.282% (percentile 20.247) as of 2026-08-27.
Detection Methods for CVE-2026-61399
Indicators of Compromise
- Unexpected use of the Lock User API or UI action initiated by non-standard administrator accounts.
- User account fields (username, display name, notes) containing HTML tags, <script> fragments, or JavaScript URI schemes.
- CloudStack management server access logs showing unusual sequences of updateUser or lockUser API calls followed by administrator UI sessions.
Detection Strategies
- Inspect the CloudStack users table and API responses for values containing angle brackets, event handlers such as onerror=, or encoded script payloads.
- Correlate management-server audit logs with browser session activity to identify administrators who viewed user records shortly after modifications by other privileged accounts.
- Monitor for anomalous administrative API calls executed from the same session that opens the CloudStack UI, indicating potential session-riding through injected script.
Monitoring Recommendations
- Enable and centralize CloudStack management-server audit logging, forwarding events to a SIEM for correlation and retention.
- Alert on privilege changes, key regeneration, and user creation events performed shortly after Lock User actions.
- Track version banners exposed by the CloudStack management server to identify hosts still running affected releases.
How to Mitigate CVE-2026-61399
Immediate Actions Required
- Upgrade Apache CloudStack to version 4.20.3.1, 4.22.1.1, or later as directed by the vendor advisory.
- Audit all administrator and domain-admin accounts, revoking any that are unused or over-privileged.
- Review user records for suspicious content in text fields and sanitize or remove entries containing markup.
Patch Information
Apache has released fixed builds in Apache CloudStack 4.20.3.1 and 4.22.1.1. See the Apache Mailing List Thread for the official announcement and release notes. Operators running any 4.20.x release up to 4.20.3.0 or any 4.21.x through 4.22.1.0 release must upgrade.
Workarounds
- Restrict access to the CloudStack management UI to trusted networks using firewall or VPN controls until patches are applied.
- Limit the number of accounts with Admin or Domain Admin roles to reduce the pool of users who could inject or trigger the payload.
- Advise administrators to avoid the Lock User workflow on unpatched systems until the upgrade is complete.
# Example: verify installed CloudStack management-server version
rpm -q cloudstack-management || dpkg -l | grep cloudstack-management
# Example: restrict management UI exposure with iptables until patched
iptables -A INPUT -p tcp --dport 8080 -s 10.0.0.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 8080 -j DROP
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
