Zimbra Collaboration Suite (ZCS) Memcached Command Injection Vulnerability (CVE-2022-27924) Security Advisory
Executive & SecOps Summary
SECOPS ASSESSMENTZimbra Collaboration Suite (ZCS) versions 8.8.15 and 9.0.
Unauthenticated remote attackers can inject arbitrary Memcached commands, leading to cache poisoning, session hijacking, and credential theft.
Immediately apply the official Zimbra security patches (9.0.0 Patch 24 / 8.8.15 Patch 31 or higher).
Affected Products & Version Scope
Remediation & Live Workaround Commands
PATCH & WORKAROUND1. Official Patch & Version Upgrade Commands
Update the Zimbra repository metadata and upgrade the patch package to the latest secure version.
# For RedHat / CentOS systems
sudo yum clean all
sudo yum update zimbra-patch -y
sudo su - zimbra -c 'zmcontrol restart'
# For Ubuntu / Debian systems
sudo apt-get update
sudo apt-get install --only-upgrade zimbra-patch -y
sudo su - zimbra -c 'zmcontrol restart'2. Temporary Workaround & Hardening Configuration
If patching cannot be applied immediately, restrict Memcached access to the local loopback interface and block external access to port 11211.
# Restrict Memcached port 11211 to localhost using iptables
sudo iptables -A INPUT -p tcp -s 127.0.0.1 --dport 11211 -j ACCEPT
sudo iptables -A INPUT -p tcp --dport 11211 -j DROP3. Log Audit & IoC Verification Commands
Inspect the Zimbra proxy and web server logs for potential injection payloads containing CRLF characters.
# Scan nginx access logs for CRLF injection attempts
grep -Ei '(%0d|%0a|\x0d|\x0a)' /opt/zimbra/log/nginx.access.log
# Verify the currently running Zimbra version and patch level
su - zimbra -c 'zmcontrol -v'Block Exploits Instantly with Managed Virtual Patching Rules
Can't patch production immediately? Deploy managed WAF rules at the edge to intercept RCE, SQLi, and deserialization payloads before they hit your origin server.
Technical Root Cause & Exploitation Mechanics
1. Vulnerability Overview & Root Cause
This vulnerability (CVE-2022-27924) exists in Zimbra Collaboration Suite (ZCS) due to insufficient input validation when processing incoming mail client requests. ZCS utilizes Memcached to cache user sessions and routing metadata. When an attacker sends a crafted HTTP request containing CRLF sequences (\r\ ), these characters are passed unescaped to the Memcached daemon, resulting in a Memcached Command Injection vulnerability (CWE-74).
2. Exploitation Mechanics & Attack Scenario
An unauthenticated attacker targets specific ZCS endpoints and injects arbitrary Memcached commands (such as 'set') via HTTP headers or query parameters. Because the input is not properly escaped, the Memcached server processes the injected commands. This allows the attacker to overwrite cached routing lookups or session tokens, effectively redirecting legitimate user traffic and credentials to an attacker-controlled server during subsequent login attempts.
3. Infrastructure & Business Impact
As a CISA KEV-listed vulnerability with an EPSS score of over 93%, this flaw is actively exploited in the wild. Successful exploitation allows attackers to compromise corporate email communications, steal sensitive business data, and gain initial access to internal networks, posing a severe threat to organizational security and compliance.
Official Vendor Advisories & References
Zimbra Collaboration (aka ZCS) 8.8.15 and 9.0 allows an unauthenticated attacker to inject arbitrary memcache commands into a targeted instance. These memcache commands becomes unescaped, causing an overwrite of arbitrary cached entries.
Frequently Asked SecOps Questions (CVE-2022-27924)
FAQQ1. How critical is CVE-2022-27924 and is it actively exploited in the wild?
CVE-2022-27924 is rated CVSS 7.5 (HIGH) with a 30-day EPSS exploitation probability of 93.9%. It is listed in the CISA Known Exploited Vulnerabilities (KEV) catalog, requiring immediate emergency remediation.
Q2. Which vendors and products are affected by CVE-2022-27924?
Primary impacted vendors include zimbra across zimbra collaboration suite, zcs. Scope summary: Zimbra Collaboration Suite (ZCS) versions 8.8.15 and 9.0 (unpatched)
Q3. What temporary mitigations or workarounds exist for CVE-2022-27924 before patching?
[Mitigation] Immediately apply the official Zimbra security patches (9.0.0 Patch 24 / 8.8.15 Patch 31 or higher). Follow the CLI remediation commands and interactive SecOps checklist on this page to restrict exposure prior to your maintenance window.
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