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THREAT SPOTLIGHT: WEB APPS UNDER ACTIVE THREAT FROM 10-YEAR-OLD SHELLSHOCK BUGS
AND MINERS

Topics:
Mar. 6, 2024
|
Tushar Richabadas
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The Shellshock bugs — there are six related CVE designations — have the highest
severity rating of 10. They exist in the Unix Bash shell, which is the default
command-line interface on all Linux, Unix, and Mac-based operating systems. If
successfully exploited, Shellshock could enable an attacker to cause Bash to
execute arbitrary commands and gain unauthorized access to many internet-facing
services, such as web servers, that use Bash to process requests.


VULNERABLE SOFTWARE UNDER ACTIVE ATTACK

The top three vulnerabilities currently being targeted with Shellshock attacks
are in the chart below. They highlight how vulnerabilities can lurk for years
undetected in the software supply chain.

A device could be running the latest version of firmware, yet still be
vulnerable, because the people creating that software did not update the
libraries in their supply chain.



CVE-2019-7481 is a 7.5 rated SQL injection vulnerability in a security service
for which a patch exists. CVE-2021-42071 is a critical 9.8 rated vulnerability
in a visual tool application that could allow an unauthenticated attacker to
achieve remote command execution.


INSTALLING MIRAI BOTNET VARIANTS

CVE-2019-7481 has been targeted since at least 2021 by attackers trying to
install Mirai botnet variants. The Mirai botnet comprises a vast number of
hacked connected (IoT) devices and is used predominantly to launch DDoS attacks.

Since Mirai first came to the forefront in August 2016, researchers have seen
multiple variants appear on the threat landscape. Mirai primarily targets IoT
Linux-based devices. Most of the attacks start by downloading a shell script
that then downloads several platform-specific malware binaries and attempts to
run them. Once infected, the device becomes part of the growing botnet.

The first two Mirai variants that we saw in our logs were going after the LuCI
web interface for OpenWRT-based routers. This is a management interface that
should not be exposed to the internet. Unfortunately, it often is, and attackers
use this to their advantage.

The first variant was used by attackers trying to execute a shell script named
“sorry.sh”.

This script is no longer available. According to URLhaus, it has been reported
and taken down. However, the analysis on URLhaus makes it clear that this is
part of a Mirai/Gafgyt infestation attempt. A more detailed description is
available on VirusTotal.



The second variant is still active.

The attackers using this variant delete everything in the root directory and
then download a shell script in /tmp.



The shell script when executed downloads several platform-specific binaries and
then executes them in order.

The developer of this specific script appears to have a sense of humor. The
downloaded files are renamed using an escalating series of insults (duly
censored in the screenshot.)


A different Mirai/Gafgyt variant was targeting a remote command execution
vulnerability in Zyxel routers. The URLhaus entry shows that this was also a
Mirai “infector” (huhu.mips) — though it is now offline. Looking at the entry
for the IP address, it is currently serving the malware with a new name
(skyljne.mips.)



CRYPTOMINER INFECTIONS TARGETING VULNERABILITIES

In addition to Shellshock, we have seen attackers targeting vulnerabilities to
install cryptominers.

Back in 2022, we saw cryptominers attempting to exploit the then new Atlassian
Confluence vulnerability. In February 2024, we are seeing active attempts to
exploit years old ThinkPHP vulnerabilities and install XMRig miners.

The first URL we saw was:


Decoding the partial base64, we find the following command:

This shows up on ANY.RUN as the XMRig miner. At the time of writing this blog,
the miner is still online.

Another example of this is:

This decodes to:


An analysis of this shell script on ANY.RUN shows that it downloads the redtail
binary as well.

A third example of this is the same 45.x IP serving a different script:


This decodes to:


Per VirusTotal, this is likely a miner too.

A final example of the miner is this one:


This decodes to:


The name of the miner in this case is not obfuscated and is directly
identifiable as XMRig. It is currently offline.

All the miner examples are targeting older ThinkPHP vulnerabilities — remote
code execution (RCE) vulnerabilities from 2018 and 2020 that should rightfully
be patched by now.


KEEPING YOUR APPLICATIONS SECURE

These types of attacks come and go in waves, with each wave — both for Mirai and
for cryptominers —targeting specific vulnerabilities in campaigns.

Around 10 years ago, attackers mainly looked for and used newer vulnerabilities
such as zero days to try to get into the network. This has shifted to attackers
working smarter, not harder. They’ve caught onto the fact that software supply
chains are rarely fully secure, and they are using older but still unpatched
vulnerabilities to their advantage.

The software supply chain security issue is quite difficult to solve — you could
deploy the latest version of your file transfer software, but under the hood
that software might be using a vulnerable version of Log4J. You assume your
application is secure, but in fact it has a known vulnerability. And the only
way to find this out is if you are running regular vulnerability scans. In the
case of Log4J, you are likely doing this. But what happens if the vulnerability
is in a relatively unknown library that is only used in this one software?

The old defense-in-depth advice remains relevant. Having a defensive “onion” for
your network and applications is crucial to preventing attacks before they can
reach your application. This approach will also give you time and aircover for
when you have not yet been able to patch a new zero day.

Protection against DDoS also remains critical. Attackers are using years old
vulnerabilities to create their botnets and perform newer types of DDoS attacks
such as HTTP/2 Rapid Reset. Having a solution in place that can stop older
volumetric DDoS attacks, and newer, subtler application DDoS attacks is critical
for business continuity.

If you look at the vulnerabilities mentioned above and in our recent application
security Threat Spotlight, you see that when it comes to applications, the
software supply chain is a weak link that needs and deserves a significant
protective layer.

Scan your web applications for vulnerabilities
Tushar Richabadas

Tushar Richabadas is Senior Product Marketing Manager, Applications and Cloud
Security, Barracuda.  Prior to this role, Tushar was a Product Manager for the
Barracuda Web Application Firewall and Barracuda Load Balancer ADC, with a focus
on cloud and automation.  Tushar has a wide range of experience, from leading
networking product testing teams and technical marketing for HCL-Cisco. Tushar
closely tracks the rapidly increasing impact of digital security and is
passionate about simplifying digital security for everyone.

Connect with him on LinkedIn here.

Related Posts:
XDR round-up 2023: High-severity threats on the rise, peak during holidays
Barracuda’s strategic distribution agreement with Ingram Micro
Threat Spotlight: How attackers are targeting your web applications right now
January webinars: New DMARC requirements, emerging application-layer threats,
and more
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