CVE-2022-27924: Zimbra Collaboration Suite RCE Vulnerability

CVE-2022-27924 Overview

CVE-2022-27924 is a command injection vulnerability affecting Zimbra Collaboration Suite (ZCS) versions 8.8.15 and 9.0. This vulnerability allows an unauthenticated attacker to inject arbitrary memcache commands into a targeted Zimbra instance. The injected commands become unescaped during processing, enabling attackers to overwrite arbitrary cached entries within the memcached service. This can lead to serious security implications including credential theft and unauthorized access to user accounts.

Critical Impact

Unauthenticated attackers can poison the memcache to steal user credentials and hijack email sessions without any prior authentication, making this vulnerability particularly dangerous for internet-facing Zimbra deployments.

Affected Products

• Zimbra Collaboration Suite 8.8.15 (all patch levels through p31)
• Zimbra Collaboration Suite 9.0.0 (all patch levels through p23)
• Synacor Zimbra Collaboration Suite

Discovery Timeline

• April 21, 2022 - CVE-2022-27924 published to NVD
• October 31, 2025 - Last updated in NVD database

Technical Details for CVE-2022-27924

Vulnerability Analysis

This vulnerability exists in how Zimbra Collaboration Suite handles user input when constructing memcache commands. The core issue stems from improper neutralization of special elements used in commands (CWE-74: Injection). When a user attempts to access their mailbox, Zimbra queries the memcached service to retrieve cached routing information. The vulnerability allows an attacker to inject CRLF (Carriage Return Line Feed) sequences and additional memcache commands through specially crafted HTTP requests.

The memcached service in Zimbra stores critical information including user session data and authentication tokens. By successfully exploiting this vulnerability, an attacker can manipulate cached entries to redirect authentication flows, potentially capturing plaintext credentials when users attempt to authenticate.

Root Cause

The root cause is insufficient input validation and lack of proper escaping when user-controlled data is incorporated into memcache protocol commands. The application fails to sanitize special characters, particularly CRLF sequences, before passing them to the memcached backend. This allows attackers to terminate the intended command and inject additional malicious memcache operations.

Attack Vector

The attack is network-based and requires no authentication, making it accessible to any attacker who can reach the Zimbra web interface. An attacker sends a specially crafted HTTP request containing memcache protocol commands embedded within user-controlled parameters. The payload typically includes CRLF injection to break out of the legitimate memcache command context.

The attacker can then set arbitrary key-value pairs in the cache. By poisoning the routing cache entries for a target user, the attacker can redirect the victim's IMAP/POP3 connection to a malicious server they control. When the victim subsequently authenticates, their credentials are sent to the attacker's server in plaintext.

Detection Methods for CVE-2022-27924

Indicators of Compromise

• Unusual HTTP requests containing CRLF sequences (%0d%0a or \r\n) in URL parameters or headers
• Unexpected modifications to memcached entries, particularly routing information
• Authentication failures followed by successful logins from unusual IP addresses
• Network connections from Zimbra servers to unknown external IMAP/POP3 servers

Detection Strategies

• Monitor web server access logs for requests containing encoded CRLF characters in URL parameters
• Implement network monitoring to detect memcache protocol commands in HTTP traffic
• Configure intrusion detection systems to alert on memcache injection patterns
• Audit memcached contents periodically for unauthorized or suspicious entries

Monitoring Recommendations

• Enable verbose logging on the Zimbra proxy and memcached services
• Deploy network-based detection for anomalous memcache traffic patterns
• Monitor for unusual outbound connections from mail infrastructure
• Implement SIEM rules to correlate authentication anomalies with suspicious HTTP requests

How to Mitigate CVE-2022-27924

Immediate Actions Required

• Update Zimbra Collaboration Suite to version 8.8.15 Patch 32 or later, or 9.0.0 Patch 24 or later immediately
• Review memcached access logs for signs of exploitation
• Restrict network access to memcached service to only necessary internal hosts
• Force password resets for users if exploitation is suspected

Patch Information

Zimbra has released security patches addressing this vulnerability. Organizations running affected versions should upgrade immediately. Patch information is available in the Zimbra Release Notes for 9.0.0 P24. Additional security guidance can be found at the Zimbra Security Center and the Zimbra Security Advisories page. Note that this vulnerability is listed in the CISA Known Exploited Vulnerabilities Catalog, indicating active exploitation in the wild.

Workarounds

• Configure firewall rules to restrict access to the memcached port (default 11211) from untrusted networks
• Implement a web application firewall (WAF) rule to block requests containing CRLF injection patterns
• Consider placing Zimbra behind a reverse proxy with strict input validation
• Monitor and audit all external access to Zimbra services until patching is complete

# Configuration example - Restrict memcached access via iptables
# Only allow connections from localhost and trusted Zimbra components
iptables -A INPUT -p tcp --dport 11211 -s 127.0.0.1 -j ACCEPT
iptables -A INPUT -p tcp --dport 11211 -s <trusted_zimbra_ip> -j ACCEPT
iptables -A INPUT -p tcp --dport 11211 -j DROP