Horizon Alert
Summary of the vulnerability and why it matters
This advisory concerns a critical vulnerability in Zimbra Classic that allows an unauthenticated attacker to potentially access mailbox data by tricking a user into clicking a malicious link. The vulnerability could enable an attacker to act on behalf of a victim, posing a significant risk to sensitive information.
- Forged email can steal user mailbox data.
- Impacts a widely used collaboration platform.
- Confirm relevance and potential exposure.
Attack Path
How an attacker could exploit the issue
An attacker can send a forged share notification to a Zimbra Classic user. When the recipient clicks on the "Accept Share" link within this notification, a stored cross-site scripting (XSS) vulnerability is triggered. This allows the attacker to potentially access the victim's mailbox data and perform actions on their behalf.
- Unauthenticated sender can send malicious notification.
- Recipient clicks "Accept Share" link.
- Attacker accesses mailbox and acts as victim.
Live Threat
Current exploitation, exposure, and threat context
An unauthenticated sender can trick a signed-in Zimbra Classic user into clicking a malicious link within a forged share notification. This action could allow an attacker to access the victim's mailbox data and perform actions as that user.
- Victim mailbox data
- Malicious link in forged notification
- Access mailbox data as victim
Operational Fix
Recommended remediation, mitigation, and detection steps
Action for this CVE likely falls to the Zimbra platform or infrastructure teams, with support from security operations for exposure analysis. The first practical step is to identify all deployed Zimbra Classic instances, confirm external reachability and business criticality, and then engage the accountable owner to plan remediation based on assessed risk.
- Platform or Infrastructure teams own resolution.
- Verify external reachability and business criticality.
- Plan remediation based on assessed risk.
