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ATT&CK Technique

Web Shell

T1505.003 · persistence

Adversaries may backdoor web servers with web shells to establish persistent access to systems. A Web shell is a Web script that is placed on an openly accessible Web server to allow an adversary to access the Web server as a gateway into a network. A Web shell may provide a set of functions to execute or a command-line interface on the system that hosts the Web server.

In addition to a server-side script, a Web shell may have a client interface program that is used to talk to the Web server (e.g. China Chopper Web shell client).

LinuxmacOSNetwork DevicesWindows
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Actors Using This

14
iranAgrius
russia_speaking_cybercrimeAkira
russia_speaking_cybercrimeALPHV / BlackCat
north_koreaAndariel
chinaAPT10
chinaAPT17
chinaAPT1
russiaAPT28
russiaAPT29
chinaAPT31
iranAPT33
iranOilRig
iranAPT35
north_koreaAPT37
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Likely Attack Path

Techniques the same actors pair with this one distinctively - those showing up among actors who use this technique noticeably more than across all actors (lift > 1.15), grouped by kill-chain phase. The × is that lift multiplier; the shared-actor count is in the tooltip. A near-universal technique pairs with everything at baseline, so its list is short by design.
reconnaissance earlier
T1596 · Search Open Technical Databases ×2.83T1589 · Gather Victim Identity Information ×2.49T1589.002 · Email Addresses ×2.46
execution earlier
T1559.002 · Dynamic Data Exchange ×2.83
persistence same
T1505 · Server Software Component ×2.76T1136.002 · Domain Account ×2.36
privilege-escalation later
T1546.001 · Change Default File Association ×2.60T1546.011 · Application Shimming ×2.55T1546.015 · Component Object Model Hijacking ×2.55
credential-access later
T1558.003 · Kerberoasting ×2.83T1003.004 · LSA Secrets ×2.43
discovery later
T1482 · Domain Trust Discovery ×2.55T1087.003 · Email Account ×2.36
exfiltration later
T1030 · Data Transfer Size Limits ×2.43
other same
T1562.003 · Impair Command History Logging ×2.83
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Atomic Tests

1
Executable Atomic Red Team test cases for exercising this technique in a lab. Copy a command, run it on the listed platform, confirm your detections fire.
command_promptwindowsWeb Shell Written to Disk
This test simulates an adversary leveraging Web Shells by simulating the file modification to disk. Idea from APTSimulator. cmd.aspx source - https://github.com/tennc/webshell/blob/master/fuzzdb-webshell/asp/cmd.aspx 
xcopy /I /Y "#{web_shells}" #{web_shell_path}
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Mitigations

2
MITRE ATT&CK mitigations - vendor-agnostic guidance for reducing exposure to this technique.
M1018User Account Management

User Account Management involves implementing and enforcing policies for the lifecycle of user accounts, including creation, modification, and deactivation. Proper account management reduces the attack surface by limiting unauthorized access, managing account privileges, and ensuring accounts are used according to organizational policies.

Enforcing the Principle of Least Privilege
  • Implementation: Assign users only the minimum permissions required to perform their job functions. Regularly audit accounts to ensure no excess permissions are granted.
  • Use Case: Reduces the risk of privilege escalation by ensuring accounts cannot perform unauthorized actions. Implementing Strong Password Policies.
  • Implementation: Enforce password complexity requirements (e.g., length, character types). Require password expiration every 90 days and disallow password reuse.
  • Use Case: Prevents adversaries from gaining unauthorized access through password guessing or brute force attacks. Managing Dormant and Orphaned Accounts.
  • Implementation: Implement automated workflows to disable accounts after a set period of inactivity (e.g., 30 days). Remove orphaned accounts (e.g., accounts without an assigned owner) during regular account audits.
  • Use Case: Eliminates dormant accounts that could be exploited by attackers. Account Lockout Policies.
  • Implementation: Configure account lockout thresholds (e.g., lock accounts after five failed login attempts). Set lockout durations to a minimum of 15 minutes.
  • Use Case: Mitigates automated attack techniques that rely on repeated login attempts. Multi-Factor Authentication (MFA) for High-Risk Accounts.
  • Implementation: Require MFA for all administrative accounts and high-risk users. Use MFA mechanisms like hardware tokens, authenticator apps, or biometrics.
  • Use Case: Prevents unauthorized access, even if credentials are stolen. Restricting Interactive Logins.
  • Implementation: Restrict interactive logins for privileged accounts to specific secure systems or management consoles. Use group policies to enforce logon restrictions.
  • Use Case: Protects sensitive accounts from misuse or exploitation.
Tools for Implementation Built-in Tools
  • Microsoft Active Directory (AD): Centralized account management and RBAC enforcement.
  • Group Policy Object (GPO): Enforce password policies, logon restrictions, and account lockout policies.
Identity and Access Management (IAM) Tools
  • Okta: Centralized user provisioning, MFA, and SSO integration.
  • Microsoft Azure Active Directory: Provides advanced account lifecycle management, role-based access, and conditional access policies.
Privileged Account Management (PAM)
  • CyberArk, BeyondTrust, Thycotic: Manage and monitor privileged account usage, enforce session recording, and JIT access.
M1042Disable or Remove Feature or Program

Disable or remove unnecessary and potentially vulnerable software, features, or services to reduce the attack surface and prevent abuse by adversaries. This involves identifying software or features that are no longer needed or that could be exploited and ensuring they are either removed or properly disabled.

Remove Legacy Software
  • Use Case: Disable or remove older versions of software that no longer receive updates or security patches (e.g., legacy Java, Adobe Flash).
  • Implementation: A company removes Flash Player from all employee systems after it has reached its end-of-life date.
Disable Unused Features
  • Use Case: Turn off unnecessary operating system features like SMBv1, Telnet, or RDP if they are not required.
  • Implementation: Disable SMBv1 in a Windows environment to mitigate vulnerabilities like EternalBlue.
Control Applications Installed by Users
  • Use Case: Prevent users from installing unauthorized software via group policies or other management tools.
  • Implementation: Block user installations of unauthorized file-sharing applications (e.g., BitTorrent clients) in an enterprise environment.
Remove Unnecessary Services
  • Use Case: Identify and disable unnecessary default services running on endpoints, servers, or network devices.
  • Implementation: Disable unused administrative shares (e.g., C$, ADMIN$) on workstations.
Restrict Add-ons and Plugins
  • Use Case: Remove or disable browser plugins and add-ons that are not needed for business purposes.
  • Implementation: Disable Java and ActiveX plugins in web browsers to prevent drive-by attacks.
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Detection Coverage

3/6 layers
Coverage across standard detection surfaces. Rows marked none have no rule of that type mapped. Some are real blind spots worth closing; others are simply not applicable to this technique (e.g. YARA matches malware files, not network behaviour).
Behavioral / log (Sigma) 23
Analytics (MITRE CAR) 1
Runtime / container (Falco) 1
File / malware (YARA) none
Network (Suricata/Snort) none
Vuln scan (Nuclei) none
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CAR Analytics

1
MITRE Cyber Analytics Repository - field-tested detection logic for this technique, written as pseudocode/queries you adapt to your own SIEM (Splunk, Sentinel, EQL). Each is a ready starting point for a detection rule, not just a description.
CAR-2021-02-001Moderate coverageWebshell-Indicative Process Tree

A web shell is a web script placed on an openly accessible web server to allow an adversary to use the server as a gatway in a network. As the shell operates, commands will be issued from within the web application into the broader server operating system. This analytic looks for host enumeration executables initiated by any web service that would not normally be executed within that environment.

Pseudocode - Pseudocode - Look for suspicious process tree beginning with web service
processes = search Process:Create
suspicious_processes = filter processes where (
  (parent_exe == "w3wp.exe" OR
   parent_exe == "httpd.exe" OR
   parent_exe == "tomcat*.exe" OR
   parent_exe == "nginx.exe" ) AND
  (exe == "cmd.exe" OR
   exe == "powershell.exe" OR
   exe == "net.exe" OR
   exe == "whoami.exe" OR
   exe == "hostname.exe" OR
   exe == "systeminfo.exe" OR
   exe == "ipconfig.exe) )
output suspicious_processes
Splunk - Splunk Search - webshell-indicative process tree
(index=__your_sysmon_index__ EventCode=1)
(ParentImage="C:\\Windows\\System32\\*w3wp.exe" OR ParentImage="*httpd.exe" OR ParentImage="*tomcat*.exe" OR ParentImage="*nginx.exe")
(Image="C:\\Windows\\System32\\cmd.exe OR Image="C:\\Windows\\SysWOW64\\cmd.exe" OR Image="C:\\Windows\\System32\\*\\powershell.exe OR Image="C:\\Windows\SysWOW64\\*\powershell.exe OR Image="C:\\Windows\\System32\\net.exe" OR Image="C:\\Windows\\System32\\hostname.exe" OR Image="C:\\Windows\\System32\\whoami.exe" OR Image="*systeminfo.exe OR Image="C:\\Windows\\System32\\ipconfig.exe")
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Falco Runtime Rules

1
Container / Linux runtime detections that fire on this technique.
CRITICALWeb Server Spawned Shell
Detects a web server process (nginx, apache, php-fpm, etc.) spawning an interactive shell. This is a strong indicator of webshell exploitation or remote code execution vulnerability being actively exploited. Webshells are a common persistence mechanism used by attackers after compromising web applications. The macro user_known_web_server_shell_activities can be overridden to tune for legitimate use cases like CGI scripts. Note that simple shell wrappers used in health checks are excluded.
view condition
spawned_process and spawned_by_web_server and proc.name in (shell_binaries) and not proc.cmdline startswith "sh -c /usr/bin" and not proc.cmdline contains "healthcheck" and not user_known_web_server_shell_activities
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Comply & Defend

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D3FEND12 defensive techniques
Intelligence Graph · click any node to traverse
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