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.
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:
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
beacons
sleep time and optional jitter (to randomize the effectivebeacons
sleep time).Staging process, which is recommended to keep disabled (
set host_stage "false"
) for OPSEC issues (identification ofteamserver
by simulating a staged beacons). If disabled, only stagelessbeacons
will be usable.The
SSL
/TLS
certificate used byHTTPS
listeners.The
HTTP
beacons
requestsURI
and parameters, theteam-server
HTTP
responses content, as well as headers (User-Agent
,Referer
,Server
, etc.).The
TCP
beacons
listening port,SMB
beacons
named pipe,SSH
beacons
banner and pipe name,DNS
beacons
parameters (subhost forA
,AAAA
,TXT
records, max query size, etc.).Post-exploitation jobs behavior, such as the program used to spawn process for injection, activation of automated
AMSI
bypass in PowerShell jobs, WindowsAPI
leveraged 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 (
PowerShell
andPython
).VBA
macro for generatedOffice
documents.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:
resources.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:
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.exe
is 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
beacon
process. 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
DLL
hooking even if the parent process is in an "unhooked" state. Under certain circumstances, theblockdlls start
command can be used to prevent userland hooking by leveraging a signature policy that blocks non-MicrosoftDLLs
from 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 ax64
process on ax64
system, it is recommended to make use ofx64
beacons as much as possible (to avoidx86
->x64
noisy injections).Self-injection uses the much less scrutinized
CreateThread
API
(by default). Specifying the currentbeacon
process for commands allowing the specification of a target process will result in self-injection. The tradeoff of self-injection is a potentialbeacon
lose if the injected code crashes or get detected and induce a kill of the process.While having other OpSec tradeoffs, the
spawnu
andrunu
commands can be used to avoid code injection by spawning, respectively, a newbeacon
or 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:
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.exe
process-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
printscreen
Take a single screenshot via PrintScr
method
screenwatch
Take periodic screenshots of desktop
spawnto <x86 | x64> <BINARY_FULL_PATH>
Local system enumeration and interaction commands
ps
Show process list
net
Network and host enumeration tool
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.
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>
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
Execute a command via powershell.exe
powerpick
Execute a command via Unmanaged PowerShell
psinject
Execute PowerShell command in specific process
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
.
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
dllload
Load DLL into a process with LoadLibrary()
Defense evasion commands
timestomp
Apply timestamps from one file to another
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
runasadmin
Execute a program in an elevated context
spawnas
Spawn a session as another user
pth pth <DOMAIN>\<USERNAME> <NTHASH>
Pass-the-hash using Mimikatz
kerberos_ccache_use
Apply Kerberos ticket from cache to this session
kerberos_ticket_purge
Purge Kerberos tickets from this session
kerberos_ticket_use
Apply Kerberos ticket to this session
Privileges and local privilege escalation commands
steal_token
Steal access token from a process
rev2self
Revert to original token
elevate
Spawn a session in an elevated context
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
remote-exec
Run a command on a remote host
Pivoting commands
Refer to [General] Pivoting - Cobalt Strike
for more information on Cobalt Strike
pivoting capabilites (rportfwd
/ rportfwd_local
, covertvpn
, and socks
commands).
browserpivot
Setup a browser pivot session
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.
covertvpn
Deploy Covert VPN client
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
ssh-key
Use SSH to spawn an SSH session on a host
socks
Start SOCKS4a server to relay traffic
socks stop
Stop SOCKS4a server
Post-exploitation commands
keylogger
Start a keystroke logger
chromedump
Recover credentials from Google Chrome
hashdump
Dump password hashes
logonpasswords
Dump credentials and hashes with mimikatz
dcsync
Extract a password hash from a DC
mimikatz
Runs a mimikatz command
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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