Hackers Are Milking an Old Apache Flaw to Deploy Linuxsys Cryptominer

Let’s talk straight: if you’re running Apache HTTP Server and you haven’t checked your version in a while, you might have a problem. An issue that’s now pretty ancient — CVE-2021-41773 — is still out there getting exploited by hackers, and they’re using it to deploy Linuxsys, a sneaky cryptocurrency miner. This isn’t your typical flash-in-the-pan malware campaign. It’s persistent, it’s clever, and honestly, it’s making a lot of admins look foolish for not locking down their setups.

And before you start thinking, “Meh, this was patched years ago,” take a breath. The exploit works because people don’t patch their systems. That’s the ugly truth. Let’s dig into what’s happening here, why this campaign is still breathing, and how you can stop it from crashing your servers.

A Flaw That Refuses to Retire

Here’s what you need to know. CVE-2021-41773 popped up in Apache HTTP Server versions 2.4.49 and 2.4.50. It’s a path traversal vulnerability, which basically means attackers can fiddle with URLs to access stuff they shouldn’t. Worse, it lets them run arbitrary code on a compromised server — effectively handing them a golden ticket to do… well, whatever they feel like.

At first glance, it seems simple: patch your system, and you’re good, right? Sure, if life were that predictable. But the reality is, there are still heaps of unpatched servers out there in the wild. Whether it’s negligence, a lack of resources, or sheer forgetfulness, the fact remains — attackers have an open door to exploit servers that are stuck running those vulnerable versions.

And here’s the kicker: the Linuxsys cryptominer isn’t even fancy. It’s just a modest little Monero-mining operation. But, as we’ll see, the hackers deploying it are pulling off some crafty moves to keep this campaign alive.

The Attack Chain, Broken Down

The Linuxsys campaign exploits vulnerable Apache servers, targeting them using tools like curl or wget and leveraging the CVE-2021-41773 vulnerability to introduce malicious payloads. Instead of hosting their own malware, the attackers rely on compromised third-party sites, like hacked WordPress domains, to distribute their files. This approach maximizes stealth and minimizes the risk of detection. Once access is obtained, a shell script named linux.sh is downloaded, which retrieves and deploys a cryptominer executable (linuxsys) along with its configuration file, config.json. These components work together to mine Monero cryptocurrency, with operations configured to connect to a specific mining pool at hashvault.pro.

To ensure persistence, the malware installs itself by creating a cron job (cron.sh) that automatically activates the miner even after a system reboot. This guarantees uninterrupted illicit activity, maximizing the use of the compromised server’s resources. Once active, the cryptominer communicates with the mining pool, effectively harnessing and draining the server’s CPU power to generate cryptocurrency profits for the attackers. The campaign exhibits a notable level of stealth and efficiency, making detection and mitigation particularly challenging.

Why Has This Campaign Stayed Alive?

Here’s the wild part: this Linuxsys operation has been kicking around since 2021. The same attack method. The same malware. And yes, the same exploit.

Why? Because people leave their systems exposed. Public telemetry tools like GreyNoise keep spotting ongoing attacks meant to exploit CVE-2021-41773. It’s a buffet for hackers — outdated servers they can hit again and again, knowing there are plenty of vulnerable targets still out there.

But there’s more to it than just neglect. The attackers are smart about dodging detection. Instead of hosting the malware themselves, they stash their payloads on legitimate servers they’ve compromised — sites with SSL certificates that make their traffic look totally benign. They’re essentially hiding in plain sight. Less flashy, more effective.

This campaign also avoids honeypots and lightly monitored systems. It’s all about targeting machines where they can get real computing resources for cryptomining. Still, even with this precision, the operation is small-scale, pulling in about $8/day. That’s peanuts. But evidently, slow and steady work if you’re patient.

How Can I Check If I am Vulnerable to CVE-2021-41773?

To check if your system is vulnerable to CVE-2021-41773, start by identifying the version of your Apache HTTP Server. Run apachectl -v or httpd -v and confirm if the version is 2.4.49, which is directly affected by this path traversal vulnerability. If Apache was installed via a package manager, use rpm -q httpd on Red Hat or CentOS systems or dpkg -l | grep apache2 on Ubuntu or Debian systems to verify the installed version. Systems running 2.4.49 should be patched immediately to 2.4.51 or later. Versions prior to 2.4.49 are not vulnerable, although upgrading is always recommended for optimal security.

You can then test for exploitation, such as attempting to access sensitive files outside the web root. Using curl, execute $ curl --path-as-is -v -k http:///../../../../etc/passwd. Here, /../../../etc/passwd directly attempts traversal, assuming the server incorrectly parses relative paths. Testing should target known vulnerable servers, and you should analyze the server''s configuration beforehand. Additionally:

• Replace  with the actual IP or hostname of the target webserver.
• Adjust the traversal depth (../) based on the suspected directory structure—specific configurations may prevent traversal beyond a defined root directory.
• Monitor the HTTP response code (e.g., 200 OK, 403 Forbidden, 404 Not Found) or content returned. A visible portion of /etc/passwd confirms exploitability.

As this vulnerability has been exploited in the wild, admins should approach remediation with urgency, applying Linux security best practices across all affected systems.

What Proactive Mitigation Steps Should Every Linux Admin Take?

Alright, let’s switch gears. If you’re reading this, you’re probably wondering how to stop this mess cold. Here’s what you should be doing, like… now:

Patch Apache Already.

Look, Apache HTTP Server patched CVE-2021-41773 ages ago. The fix landed with version 2.4.51 back in October 2021. Upgrade. Your. Server. No excuses.

Block Staging Domains.

Add rules in your firewall to prevent traffic to known malicious domains:

• repositorylinux.org
• Other compromised WordPress sites — if you’re unsure, check VulnCheck or relevant domain blocklists.

Lock Down Configuration.

Disable unused Apache modules, restrict access to directories, and periodically audit your server’s settings to catch potential misconfigurations.

Use Network- and Host-Level Defenses.

Deploy tools like Suricata or Snort to detect attempts at exploiting CVE-2021-41773. Install endpoint protection to keep an eye out for unusual processes, like cryptominer binaries running where they shouldn’t.

Monitor Resource Usage and Traffic.

Check CPU and memory usage for unexplained spikes. Also, scan outgoing traffic for TLS connections tied to cryptomining pools like pool.hashvault.pro. If your system’s churning out megahashes, something’s wrong.

What Are the Risks of Dropping the Ball?

Ignore this issue long enough, and here’s what you’ll face:

• System Slowdown: Your servers will be crawling under the weight of mining tasks — bad news for uptime and performance.
• Power Bills Spike: Mining cryptocurrency burns energy. It’s your money getting flushed down the drain here.
• Reputation Damage: If your system gets hijacked, it could be leveraged for broader attacks, like staging phishing campaigns or hosting more malware. Not a good look.

Of course, there’s always the lurking risk that cryptominers are just the beginning. Attackers with full access to your server could pivot deeper into your network. Why stop at installing malware when you also have sensitive data to steal?

The Main Takeaway: Prevention Is Far Better Than Reaction

This Linuxsys campaign isn’t big. It’s not glamorous. But it’s a firm reminder of why old vulnerabilities like CVE-2021-41773 can’t just be ignored — especially when they’re straightforward to fix.

The hackers behind this campaign have managed to stretch their operation years past its prime by exploiting the same flaw over and over. That’s embarrassing. For them? Not really. For us admins who should’ve patched things up long ago? Absolutely.

So, check your versions and get them patched already. Don’t hand bad actors free resources to mine Monero at your expense. And while you’re at it, tighten up your monitoring and configuration — even the smallest mistake can leave you wide open.