CVE-2026-61398 Overview
CVE-2026-61398 is an Improper Encoding or Escaping of Output vulnerability [CWE-116] in the Apache CloudStack web user interface. The flaw resides in the Instance Reset Password functionality, where output is rendered without proper encoding. An attacker can leverage this weakness to inject and execute arbitrary content in the context of the CloudStack UI over the network without authentication.
The vulnerability affects Apache CloudStack versions 4.15.1.0 through 4.20.3.0 and 4.21.0.0 through 4.22.1.0. The Apache CloudStack project has released fixed versions 4.20.3.1 and 4.22.1.1.
Critical Impact
Network-exploitable output escaping flaw in the CloudStack management UI that can compromise the confidentiality and integrity of hosted virtual infrastructure.
Affected Products
- Apache CloudStack 4.15.1.0 through 4.20.3.0
- Apache CloudStack 4.21.0.0 through 4.22.1.0
- Deployments exposing the CloudStack management UI to untrusted networks
Discovery Timeline
- 2026-08-21 - CVE-2026-61398 published to NVD
- 2026-08-27 - Last updated in NVD database
Technical Details for CVE-2026-61398
Vulnerability Analysis
Apache CloudStack is an open-source cloud orchestration platform used to manage large-scale virtualized infrastructure. The management UI provides administrative operations, including the Instance Reset Password workflow. This workflow returns instance-related data to the browser without applying proper output encoding or escaping.
Because the UI trusts the returned data during rendering, attacker-controlled input embedded in reset-password responses can break out of its intended context. The result is script or markup injection inside an authenticated administrative session. Successful exploitation can be used to steal session tokens, issue privileged CloudStack API calls, or alter tenant resources.
Root Cause
The root cause is a violation of [CWE-116]: Improper Encoding or Escaping of Output. Data returned to the UI during the Instance Reset Password flow is not consistently HTML-encoded before being rendered. Fields that should be treated as inert text are instead interpreted by the browser, enabling injection into the DOM.
Attack Vector
The vulnerability is exploitable over the network with low attack complexity and no privileges or user interaction required. An attacker who can influence the data returned by the Instance Reset Password functionality can trigger unsafe rendering in the UI of any operator or tenant user viewing the resulting page. The bug impacts confidentiality and integrity of the CloudStack control plane; availability is not directly affected.
No verified public proof-of-concept has been published for this issue. Refer to the Apache Mailing List Discussion for the vendor announcement and remediation guidance.
Detection Methods for CVE-2026-61398
Indicators of Compromise
- CloudStack UI responses under the Instance Reset Password workflow containing HTML tags, <script> fragments, or JavaScript event handlers inside instance metadata fields.
- Unexpected outbound requests from administrator browsers to unknown domains shortly after loading the CloudStack management console.
- Creation or modification of CloudStack API keys, users, or instances immediately following an administrator session interacting with reset-password views.
Detection Strategies
- Inspect CloudStack management-server.log and access logs for reset-password API calls that return payloads containing markup or script characters in instance name, display name, or template fields.
- Deploy web application firewall rules that flag responses from CloudStack UI endpoints containing unescaped <, >, or on*= attributes in JSON string values.
- Correlate administrator UI sessions with subsequent privileged CloudStack API activity originating from unexpected source addresses.
Monitoring Recommendations
- Enable verbose audit logging on the CloudStack management server and forward logs to a centralized analytics platform for retention and correlation.
- Alert on administrator account activity that occurs outside normal maintenance windows or from new user agents.
- Baseline the size and structure of Instance Reset Password responses to detect anomalous payloads consistent with injected content.
How to Mitigate CVE-2026-61398
Immediate Actions Required
- Upgrade Apache CloudStack to version 4.20.3.1, 4.22.1.1, or later as instructed by the Apache Mailing List Discussion.
- Restrict access to the CloudStack management UI to trusted administrative networks and VPN endpoints.
- Rotate CloudStack administrator credentials and API keys after patching to invalidate any sessions that may have been abused.
Patch Information
The Apache CloudStack project fixed CVE-2026-61398 in versions 4.20.3.1 and 4.22.1.1. Operators running any release in the 4.15.1.0–4.20.3.0 or 4.21.0.0–4.22.1.0 ranges must upgrade to a fixed release. No official configuration-only fix is provided by the vendor.
Workarounds
- Limit use of the Instance Reset Password feature until the management server is upgraded to a fixed version.
- Enforce a strict Content Security Policy on the CloudStack UI hostname to reduce the impact of injected script content.
- Require administrators to access the CloudStack UI through a reverse proxy that performs response inspection and blocks script content in JSON API responses.
# Verify installed Apache CloudStack management server version
rpm -q cloudstack-management 2>/dev/null || dpkg -l | grep cloudstack-management
# Example: upgrade path check against fixed releases
# Target versions: 4.20.3.1 or 4.22.1.1 or later
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
