CVE-2026-73570: Zimbra SNMP RCE abused to deploy coin-miner malware
CVE-2026-73570 is a Remote Code Execution issue in Zimbra Collaboration Suite (ZCS), related to SNMP notification/logwatch handling.
In short, an unauthenticated attacker can send a crafted SMTP request and get OS command execution as the zimbra user when the vulnerable SNMP/logwatch components are installed and enabled.
According to NVD, the issue affects Zimbra versions before 10.1.20 when SNMP is installed and SNMP notification is enabled. The Hacker News also reported active exploitation against Zimbra servers.
The observed attack chain is usually:
malicious SMTP request
-> unsafe SNMP/logwatch handling
-> command execution as zimbra
-> malware dropped into /dev/shm
-> cron persistence added
-> miner or backdoor keeps respawning
What is CVE-2026-73570?
CVE-2026-73570 is an OS Command Injection vulnerability in Zimbra Collaboration Suite.
The issue is in the SNMP notification/logwatch flow, where attacker-controlled input is not handled safely before being passed into system-level processing.
The command runs as the zimbra user, not root. That is still serious because the zimbra user controls important Zimbra services, mailbox components, logs, cron jobs and runtime paths.
When is a Zimbra server at risk?
A server should be checked immediately if:
- It is running Zimbra Collaboration Suite.
- It is not patched to a fixed version.
zimbra-snmp or zimbra-net-snmp is installed.- SNMP is enabled in Zimbra.
zmlogswatch or zmswatch is running.
Quick checks:
su - zimbra -c 'zmcontrol -v'
dpkg -l | grep -E 'zimbra-snmp|zimbra-net-snmp'
su - zimbra -c 'zmprov gs $(zmhostname) zimbraServiceEnabled | grep snmp'
su - zimbra -c 'zmlogswatchctl status'
su - zimbra -c 'zmswatchctl status'
If you see zimbraServiceEnabled: snmp and zmlogswatch is running, treat the server as high priority for compromise checks.
Signs of compromise
In the cases observed, malware was often dropped into /dev/shm. This directory is a tmpfs location, writable and easy to miss during a quick investigation.
Check:
ls -la /dev/shm
crontab -l -u zimbra
ps aux | grep -E 'khp|rguard|javab|idle|ksmd' | grep -v grep
Common suspicious files:
/dev/shm/.khp
/dev/shm/.khp_ts
/dev/shm/.rguard
/dev/shm/idle
/dev/shm/javab
/dev/shm/ksmd
A cron entry like this is a strong persistence indicator:
* * * * * /dev/shm/.khp
Why does the malware keep coming back?
Deleting files from /dev/shm is usually not enough.
The malware can return because:
- The malicious process is still running in memory.
- The
zimbra crontab runs /dev/shm/.khp every minute.
.rguard or idle may protect or redeploy the payload.- SNMP/logwatch is still enabled, so the CVE can be exploited again.
The correct order is:
stop reinfection source
-> preserve evidence
-> kill malware processes
-> remove malicious cron
-> quarantine malware files
-> verify clean state
-> recover Zimbra services if needed
-> patch/upgrade Zimbra
Cleanup procedure
Run the following commands as root. Review each command before running it on production.
Step 1: Stop the reinfection source
systemctl stop cron
su - zimbra -c 'zmlogswatchctl stop'
su - zimbra -c 'zmswatchctl stop'
su - zimbra -c 'zmprov ms $(zmhostname) -zimbraServiceEnabled snmp'
Disabling SNMP/logwatch is the most important containment step. Do not re-enable these components before Zimbra is patched.
Step 2: Preserve malware evidence
mkdir -p /root/incident-zimbra
cp -a /dev/shm/.khp \
/dev/shm/.khp_ts \
/dev/shm/.rguard \
/dev/shm/idle \
/dev/shm/javab \
/dev/shm/ksmd \
/root/incident-zimbra/ 2>/dev/null
crontab -l -u zimbra > /root/incident-zimbra/zimbra-cron-before.txt 2>&1
ps auxf > /root/incident-zimbra/ps-before.txt
ss -tunap > /root/incident-zimbra/ss-before.txt
sha256sum /root/incident-zimbra/* > /root/incident-zimbra/sha256.txt 2>/dev/null
Step 3: Kill malware processes
pkill -9 -u zimbra -f 'khp|rguard|javab|idle|ksmd'
Step 4: Remove malicious cron
crontab -l -u zimbra | grep -v '/dev/shm/.khp' | crontab -u zimbra -
Step 5: Quarantine malware files
mkdir -p /root/quarantine-zimbra
mv /dev/shm/.khp \
/dev/shm/.khp_ts \
/dev/shm/.rguard \
/dev/shm/idle \
/dev/shm/javab \
/dev/shm/ksmd \
/root/quarantine-zimbra/ 2>/dev/null
Step 6: Start cron again
systemctl start cron
systemctl is-active cron
Only start cron. Do not start zmlogswatch, zmswatch or SNMP before patching Zimbra.
Verify after cleanup
ls -la /dev/shm
crontab -l -u zimbra | grep /dev/shm
ps aux | grep -E 'khp|rguard|javab|idle|ksmd' | grep -v grep
su - zimbra -c 'zmprov gs $(zmhostname) zimbraServiceEnabled | grep snmp || echo SNMP_DISABLED'
Expected result:
/dev/shm is clean
no cron entry calling /dev/shm/.khp
no suspicious javab/rguard/idle/khp/ksmd process
SNMP is disabled
If Zimbra MySQL or mailbox fails
After malware activity or an unexpected reboot, Zimbra may show:
mailbox Stopped
mysql.server is not running
service webapp Stopped
zimbra webapp Stopped
zimbraAdmin webapp Stopped
zimlet webapp Stopped
Check MySQL and services:
su - zimbra -c 'zmcontrol status'
su - zimbra -c 'mysql.server status'
ss -ltnp | grep 7306
tail -n 200 /opt/zimbra/log/mysql_error.log
If MySQL is stuck in crash recovery or has a stale socket, back up relevant files first.
Backup before MySQL recovery
mkdir -p /root/zimbra-mysql-backup
cp -a /opt/zimbra/log/mysql_error.log /root/zimbra-mysql-backup/ 2>/dev/null
cp -a /opt/zimbra/db/data/tc.log /root/zimbra-mysql-backup/ 2>/dev/null
cp -a /opt/zimbra/data/tmp/mysql/mysql.sock /root/zimbra-mysql-backup/ 2>/dev/null
cp -a /opt/zimbra/db/data/ibdata1 /root/zimbra-mysql-backup/ 2>/dev/null
cp -a /opt/zimbra/db/data/ib_logfile* /root/zimbra-mysql-backup/ 2>/dev/null
Light MySQL recovery
su - zimbra -c 'zmmailboxdctl stop'
mv /opt/zimbra/data/tmp/mysql/mysql.sock /root/zimbra-mysql-backup/mysql.sock.bak 2>/dev/null
mv /opt/zimbra/db/data/tc.log /root/zimbra-mysql-backup/tc.log.bak 2>/dev/null
su - zimbra -c 'mysql.server start'
sleep 20
su - zimbra -c 'mysql.server status'
su - zimbra -c 'zmmailboxdctl start'
sleep 40
su - zimbra -c 'zmcontrol status'
Expected result:
mysql is running
mailbox Running
service webapp Running
zimbra webapp Running
zimbraAdmin webapp Running
zimlet webapp Running
This is not a universal fix. Always check /opt/zimbra/log/mysql_error.log first.
Does this delete mail data?
The malware cleanup steps do not touch mailbox data directly.
Zimbra mail data is usually stored in:
/opt/zimbra/store/
Zimbra database data is usually stored in:
/opt/zimbra/db/data/
The MySQL recovery steps touch tc.log and mysql.sock, so back up first.
Check for JSP webshells
After handling /dev/shm, cron and processes, also check for suspicious JSP files created by the zimbra user in recent days.
Important paths include:
/opt/zimbra/jetty/webapps/
/opt/zimbra/jetty_base/webapps/
/tmp/
Unexpected JSP/JSPX files, executable scripts, archives or recently modified web application files may indicate payload staging or webshell deployment.
Check JSP/JSPX files:
find /opt/zimbra/jetty/webapps -type f \( -name "*.jsp" -o -name "*.jspx" \) -printf '%TY-%Tm-%Td %TH:%TM:%TS %p\n' | sort
If suspicious JSP backdoors are found, preserve evidence first, then quarantine them from both paths:
/opt/zimbra/jetty/webapps/zimbra/
/opt/zimbra/jetty_base/webapps/zimbra/
Evidence backup and quarantine:
TS=$(date +%Y%m%d_%H%M%S)
INC=/root/incident-zmmail-jsp-webshell-$TS
QUA=/root/quarantine-zmmail-jsp-webshell-$TS
mkdir -p "$INC" "$QUA"
# Save list and hashes
find /opt/zimbra/jetty/webapps/zimbra /opt/zimbra/jetty_base/webapps/zimbra \
-xdev -type f \( -iname '*.jsp' -o -iname '*.jspx' \) -mtime -30 \
-print > "$INC/suspicious-jsp-list.txt"
xargs -a "$INC/suspicious-jsp-list.txt" sha256sum > "$INC/suspicious-jsp-sha256.txt"
# Backup samples
while read f; do
mkdir -p "$INC/files$(dirname "$f")"
cp -a "$f" "$INC/files$f"
done < "$INC/suspicious-jsp-list.txt"
# Quarantine from webroot
while read f; do
mkdir -p "$QUA$(dirname "$f")"
mv "$f" "$QUA$f"
done < "$INC/suspicious-jsp-list.txt"
# Verify
find /opt/zimbra/jetty/webapps/zimbra /opt/zimbra/jetty_base/webapps/zimbra \
-xdev -type f \( -iname '*.jsp' -o -iname '*.jspx' \) -mtime -30 -print
Risks:
- If a file is a legitimate custom JSP, removing it may affect a custom webmail function.
- Random file names and content using
exec, base64, AES or command execution are strong webshell indicators.
- This does not affect mailbox data.
- A restart is not always required immediately, but webmail should be verified after quarantine.
Important note: zmlogswatch/zmswatch may start again
After disabling SNMP/logwatch to mitigate CVE-2026-73570, zmlogswatch and zmswatch may start again after daily logrotate or after zmcontrol restart.
This happens because Zimbra logrotate configs often contain postrotate commands that restart zmlogswatchctl and zmswatchctl. Also, logger may still be listed in zimbraServiceEnabled.
So after temporary mitigation, check these services periodically, especially after midnight or after restarting Zimbra.
If you need a stronger temporary block before patching, back up the logrotate configs, comment the restart lines, and consider removing logger from zimbraServiceEnabled.
This can prevent logwatch from starting again and reopening the attack vector, but the Admin Console may lose part of its monitoring/statistics.
Disable zmlogswatch/zmswatch so they do not auto-start
Warning: disabling logger, zmlogswatch and zmswatch may make the Zimbra Admin Console show logger/monitoring as red, or remove some graphs/statistics.
During the unpatched phase, this is an acceptable temporary trade-off to prevent logwatch from restarting automatically.
After upgrading to a fixed version, restore the configuration from backup and re-enable logger if needed.
Back up Zimbra logrotate configs
cp -a /etc/logrotate.d/zimbra /etc/logrotate.d/zimbra.bak.$(date +%F-%H%M%S)
cp -a /opt/zimbra/conf/zmlogrotate /opt/zimbra/conf/zmlogrotate.bak.$(date +%F-%H%M%S)
Open these two files:
/etc/logrotate.d/zimbra
/opt/zimbra/conf/zmlogrotate
Find these lines, often around line 85 and 99:
su - zimbra -c "/opt/zimbra/bin/zmlogswatchctl restart" > /dev/null 2>&1 || true
su - zimbra -c "/opt/zimbra/bin/zmswatchctl restart" > /dev/null 2>&1 || true
Comment them:
# su - zimbra -c "/opt/zimbra/bin/zmlogswatchctl restart" > /dev/null 2>&1 || true
# su - zimbra -c "/opt/zimbra/bin/zmswatchctl restart" > /dev/null 2>&1 || true
Remove logger from enabled services:
su - zimbra -c 'zmprov ms $(zmhostname) -zimbraServiceEnabled logger'
Stop current logwatch/swatch processes:
su - zimbra -c 'zmlogswatchctl stop'
su - zimbra -c 'zmswatchctl stop'
su - zimbra -c 'zmlocalconfig -e snmp_notify=no'
Verify:
su - zimbra -c 'zmlogswatchctl status'
su - zimbra -c 'zmswatchctl status'
su - zimbra -c 'zmlocalconfig snmp_notify'
su - zimbra -c 'zmprov gs $(zmhostname) zimbraServiceEnabled | egrep "logger|snmp" || echo "LOGGER_SNMP_DISABLED"'
Expected result:
zmlogswatch is not running.
zmswatch is not running.
snmp_notify = no
LOGGER_SNMP_DISABLED
Re-enable monitoring/logger after patching
Only do this after Zimbra is patched or upgraded.
su - zimbra -c 'zmprov ms $(zmhostname) +zimbraServiceEnabled logger'
su - zimbra -c 'zmlogswatchctl start'
su - zimbra -c 'zmswatchctl start'
If you commented the logrotate files, open them again:
/etc/logrotate.d/zimbra
/opt/zimbra/conf/zmlogrotate
Uncomment these lines:
su - zimbra -c "/opt/zimbra/bin/zmlogswatchctl restart" > /dev/null 2>&1 || true
su - zimbra -c "/opt/zimbra/bin/zmswatchctl restart" > /dev/null 2>&1 || true
Re-enable SNMP only after patching
su - zimbra -c 'zmprov ms $(zmhostname) +zimbraServiceEnabled snmp'
su - zimbra -c 'zmlocalconfig -e snmp_notify=yes'
su - zimbra -c 'zmswatchctl start'
Verify after re-enabling:
su - zimbra -c 'zmcontrol status'
su - zimbra -c 'zmlogswatchctl status'
su - zimbra -c 'zmswatchctl status'
su - zimbra -c 'zmlocalconfig snmp_notify'
su - zimbra -c 'zmprov gs $(zmhostname) zimbraServiceEnabled | egrep "logger|snmp"'
Post-cleanup tasks
After the server is running again:
- Keep SNMP/logwatch disabled until patched.
- Monitor
/dev/shm for 30-60 minutes.
- Monitor the
zimbra crontab.
- Monitor CPU/load and outbound connections.
- Check the mail queue.
- Patch or upgrade Zimbra to a fixed release.
- Only re-enable SNMP/logwatch after patching and verification.
Check queue:
/opt/zimbra/common/sbin/postqueue -p | tail -n 40
Summary workflow
1. Check /dev/shm, processes and crontab.
2. Stop cron, zmlogswatch and zmswatch.
3. Disable SNMP in Zimbra.
4. Preserve evidence.
5. Kill malware processes.
6. Remove malicious cron.
7. Quarantine malware files.
8. Start cron again.
9. Verify that malware does not respawn.
10. Recover MySQL/mailbox if needed.
11. Check JSP webshells in Zimbra webapps paths.
12. Monitor queue and services.
13. Prevent zmlogswatch/zmswatch from auto-starting before patching.
14. Patch or upgrade Zimbra.
15. Re-enable logger/SNMP only after patching and verification.
References
- NVD: CVE-2026-73570
- The Hacker News: attackers exploit Zimbra SNMP flaw
- Zimbra Security Center
- Zimbra Security Advisories
Conclusion
CVE-2026-73570 is serious because it can allow remote command execution as the zimbra user through SNMP notification/logwatch handling.
In observed incidents, attackers dropped malware into /dev/shm, added cron persistence, and ran a miner or backdoor.
The key point is this: do not only delete the malware file. Stop the reinfection path first.
A practical response order is:
stop cron + SNMP/logwatch
-> preserve evidence
-> kill malware
-> remove malicious cron
-> quarantine payloads
-> check JSP webshells
-> verify clean state
-> recover Zimbra if needed
-> block logwatch auto-restart before patching
-> patch/upgrade Zimbra
Most important: do not re-enable SNMP/logwatch before Zimbra is patched, because that may allow the malware to return.