Mirai worm exploits cPanel/WHM flaw for spike
JPCERT/CC's TSUBAME sensors saw a sharp Mirai-like scan surge on 23/TCP in early May 2026 linked to exploitation of a cPanel/WHM auth-bypass flaw (CVE-2026-41940).
Sourceblogs.jpcert.or.jp — open the original
What to check
- Applies to
- The 1 CVE named below. Whether you run an affected version is not assessed: check the versions the source lists.
- Exploitation
- CISA lists CVE-2026-41940 as exploited in the wild.
JPCERT/CC's quarterly TSUBAME internet threat monitoring report for April-June 2026 highlights a notable spike in Mirai-like packets targeting port 23/TCP beginning April 30, 2026, peaking in early May before gradually declining. Source IP analysis showed many originating from hosting-provider IP ranges running cPanel administration interfaces, suggesting server (not just IoT device) compromise. Correlating with external reporting from Censys and Japan's NICTER Analysis Team, JPCERT/CC assesses the surge was likely associated with Mirai or variant infection activity exploiting a cPanel/WHM authentication bypass vulnerability (CVE-2026-41940), which allows attackers to bypass authentication and compromise affected hosting servers. The activity was globally distributed, with the United States seeing the largest share and notable increases also in Germany, France, and Canada; Japanese sensor traffic rose roughly 15x above baseline during the peak, indicating broad, non-regionally-concentrated scanning/infection rather than a targeted campaign.
Beyond the Mirai spike, the report notes routine scanning trends: 23/TCP remained the most commonly targeted port across most sensors, with 443/TCP, 80/TCP, 8080/TCP, and 22/TCP also broadly observed, indicating continuous wide-scale internet scanning rather than anomalous activity. JPCERT/CC states no other unusual activity warranted a special alert this quarter.
For defenders, particularly those operating cPanel/WHM-based hosting infrastructure, the key action is to patch against CVE-2026-41940 promptly, restrict remote/administrative access, and enforce strong credentials. Because Mirai variants can now compromise servers in addition to IoT devices, incident responders should review running processes and outbound network connections for signs of botnet activity even on non-IoT infrastructure with cPanel/WHM installed.
Mentioned in this report
Detection guidance
cPanel/WHM Process Spawning Network Scanning Tools
A behavioural hunt for the technique in general, not a signature for the CVEs this report names.
Detects cPanel/WHM-related processes launching tools commonly used for reconnaissance (netcat, curl, wget) or spawning shells, indicative of post-exploitation activity. Auto-generated starting point — validate and tune in your environment before deploying. IOC matches can false-positive on shared infrastructure and decay as adversary infrastructure rotates.
title: cPanel/WHM Process Spawning Network Scanning Tools
description: Detects cPanel/WHM daemon processes (or their children) spawning reconnaissance
or shell tools, consistent with post-exploitation behaviour after CVE-2026-41940
or similar auth-bypass compromise.
tags:
- attack.t1190
logsource:
category: process_creation
product: linux
detection:
selection_parent:
ParentImage|contains:
- cpanel
- whm
- cpsrvd
selection_child:
Image|endswith:
- /nc
- /ncat
- /curl
- /wget
- /sh
- /bash
filter_legitimate:
User: root
CommandLine|contains:
- backup
- update
- maintenance
condition: (selection_parent and selection_child) and not filter_legitimate
falsepositives:
- cPanel update or backup processes legitimately invoking curl/wget
- Shell spawned for routine cPanel administrative tasks
level: medium
id: 88d82c23-d6f8-5959-8b33-7f2887a5e921
status: experimental
author: Vorant
Behavioural rules are generated from public reporting — validate in your environment before deploying.
Source reporting: https://blogs.jpcert.or.jp/en/2026/09/tsubame_overflow_2026-04-06.html
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