CVE-2026-23918: Apache HTTP Server HTTP/2 Double Free — Detection and Hardening Guide

---
title: Apache HTTPd Spawning Shell - Potential RCE
id: 8a4d3b21-1c9e-4f5a-8b2d-9e3f1a4b5c6d
status: experimental
description: Detects the Apache HTTP Server parent or child process spawning a shell, which is abnormal behavior and indicative of successful code execution (e.g., CVE-2026-23918).
author: Security Arsenal
date: 2026/05/15
references:
 - https://httpd.apache.org/security/vulnerabilities_24.html
 - https://nvd.nist.gov/vuln/detail/CVE-2026-23918
tags:
 - attack.execution
 - attack.initial_access
 - attack.t1190
logsource:
 category: process_creation
 product: linux
detection:
 selection:
   ParentImage|endswith:
     - '/httpd'
     - '/apache2'
   Image|endswith:
     - '/sh'
     - '/bash'
     - '/dash'
     - '/zsh'
     - '/tcsh'
   # Exclude known legitimate CGI scripts that might use shells if necessary, 
   # though modern stacks rarely invoke shell directly from httpd parent.
 condition: selection
falsepositives:
 - Legitimate administrative CGI scripts (rare)
 - Misconfigured legacy web applications
level: critical
---
title: Apache HTTPd Process Crash/Restart Loop
id: 9b5e4c32-2d0f-5g6b-0c3e-0f4g2b5c6d7e
status: experimental
description: Detects rapid restarts or segmentation faults in the Apache HTTP Server process, which may indicate exploitation attempts causing DoS (CVE-2026-23918).
author: Security Arsenal
date: 2026/05/15
references:
 - https://httpd.apache.org/security/vulnerabilities_24.html
tags:
 - attack.impact
 - attack.t1499
logsource:
 product: linux
 service: syslog
detection:
 selection:
   program|contains:
     - 'httpd'
     - 'apache2'
   message|contains:
     - 'segfault'
     - 'core dumped'
     - 'Segmentation fault'
 condition: selection
falsepositives:
 - Other software bugs or misconfigurations
level: high

// Hunt for Apache httpd spawning shells
DeviceProcessEvents
| where Timestamp > ago(1d)
| where InitiatingProcessFileName has "httpd" or InitiatingProcessFileName has "apache2"
| where FileName in~ ("sh", "bash", "dash", "zsh", "tcsh", "ksh")
| extend HostName = DeviceName
| project Timestamp, HostName, AccountName, FileName, InitiatingProcessFileName, ProcessCommandLine, InitiatingProcessCommandLine
| order by Timestamp desc

-- Hunt for Apache httpd spawning shell processes
SELECT Pid, Ppid, Name, Exe, Username, StartTime, CommandLine
FROM pslist()
WHERE Ppid IN (
    -- Find PIDs of all httpd processes
    SELECT Pid FROM pslist() WHERE Name =~ 'httpd' OR Name =~ 'apache2'
)
AND (Name =~ 'sh' OR Name =~ 'bash' OR Name =~ 'dash' OR Name =~ 'zsh')

#!/bin/bash

# Security Arsenal Remediation Script for CVE-2026-23918
# Checks Apache version and mitigates by disabling HTTP/2 if needed.

APACHE_BIN=$(command -v httpd || command -v apache2)
VULN_VERSIONS="2.4.0 2.4.1 2.4.2 2.4.3 2.4.4 2.4.5 2.4.6 2.4.7 2.4.8 2.4.9 2.4.10 2.4.11 2.4.12 2.4.13 2.4.14 2.4.15 2.4.16 2.4.17 2.4.18 2.4.19 2.4.20 2.4.21 2.4.22 2.4.23 2.4.24 2.4.25 2.4.26 2.4.27 2.4.28 2.4.29 2.4.30 2.4.31 2.4.32 2.4.33 2.4.34 2.4.35 2.4.36 2.4.37 2.4.38 2.4.39 2.4.40 2.4.41 2.4.42 2.4.43 2.4.44 2.4.45 2.4.46 2.4.47 2.4.48 2.4.49 2.4.50 2.4.51 2.4.52 2.4.53 2.4.54 2.4.55 2.4.56 2.4.57 2.4.58 2.4.59 2.4.60 2.4.61"
FIXED_VERSION="2.4.62"

if [ -z "$APACHE_BIN" ]; then
    echo "[+] Apache HTTP Server not found on this system."
    exit 0
fi

echo "[*] Checking Apache version..."
CURRENT_VERSION=$($APACHE_BIN -v | grep -oP 'Server version: Apache/\K[0-9.]+' | head -n1)
echo "[!] Detected Version: $CURRENT_VERSION"

# Simple version check logic (assumes standard version strings)
if [ "$CURRENT_VERSION" == "$FIXED_VERSION" ]; then
    echo "[+] System is running the patched version."
    exit 0
fi

echo "[!] WARNING: Version $CURRENT_VERSION may be vulnerable to CVE-2026-23918."
echo "[*] Recommendation: Update to Apache $FIXED_VERSION or later immediately."
echo ""
echo "[*] Mitigation Option: If you cannot patch immediately, consider disabling HTTP/2."
echo "[*] To disable HTTP/2, comment out 'Protocols h2 http/1.1' or 'H2Direct on' in your configuration."
echo "[*] Common config locations: /etc/httpd/conf/httpd.conf or /etc/apache2/mods-enabled/http2.conf"

# Example mitigation command (Requires root and proper path knowledge)
# read -p "Disable HTTP/2 now? (y/n): " -n 1 -r
# echo
# if [[ $REPLY =~ ^[Yy]$ ]]; then
#     a2dismod http2
#     systemctl restart apache2
#     echo "[+] HTTP/2 disabled and service restarted."
# fi