Horizon Alert
Summary of the vulnerability and why it matters
A vulnerability has been identified within Zimbra Collaboration Suite's Classic Web Client. This flaw stems from how the system handles HTML content within ICS files, specifically an insufficient sanitization process. When a user interacts with an email containing a specially crafted ICS entry, a weakness in the handling of the `ontoggle` event within a `<details>` tag allows for the execution of arbitrary JavaScript. This can lead to unauthorized actions performed within the victim's session.
- Vulnerable component: Zimbra Classic Web Client
- Core weakness: Insufficient HTML sanitization in ICS files
- Main business impact: Unauthorized account actions, data exfiltration
Attack Path
How an attacker could exploit the issue
The attack path involves an attacker exploiting a stored cross-site scripting vulnerability within the Zimbra Collaboration Suite's Classic Web Client. This vulnerability arises from inadequate sanitization of HTML content found in calendar invitation (ICS) files. By embedding malicious JavaScript within an ICS file, an attacker can trick a user into opening an email containing this entry. When the user views this malicious ICS entry, the embedded JavaScript executes, allowing the attacker to gain control over actions within the victim's session. This can lead to unauthorized modifications, such as setting up email filters to redirect messages.
- External access to the email system.
- Malicious ICS file sent via email.
- User views email; JavaScript executes.
- Attacker performs unauthorized actions.
Live Threat
Current exploitation, exposure, and threat context
A stored cross-site scripting vulnerability has been identified in Zimbra Collaboration Suite. This vulnerability allows for the execution of arbitrary JavaScript within a user's session when they view a specially crafted email. Attackers can leverage this to perform unauthorized actions on a victim's account, such as redirecting emails or exfiltrating data. The potential for unauthorized actions on user accounts indicates a significant business risk.
- Likely attacker skill level: Low
- Required access or conditions: Authenticated user, user interaction
- Business risk or urgency: High
Priority actions
Operational Fix
Recommended remediation, mitigation, and detection steps
This vulnerability in Zimbra Collaboration Suite could allow an attacker to execute arbitrary JavaScript within a user's session, potentially leading to unauthorized actions such as redirecting emails or exfiltrating data. The risk arises from the insufficient sanitization of HTML content within ICS files, which can be triggered when a user views a malicious email. This could impact affected organizations by compromising user accounts and sensitive information.
- Identify exposed Zimbra Collaboration assets.
- Mitigate exposure or isolate affected systems.
- Apply vendor fixes and validate.
- Monitor for related malicious activity.
