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Random freezes, missing sound and display glitches usually trace back to one bad driver. Find and replace yours safely.Free scan · under a minuteDarkleech was the name used for a 2013 campaign that compromised Linux web servers and used rogue Apache modules to inject hidden, conditional iframes into sites hosted on them. Cisco’s often-repeated figure of about 20,000 affected websites was an estimate—not a verified count of individual sites.
What was the Darkleech malware?
Darkleech was a server-side attack campaign reported in 2013. Rather than breaking into each website separately, attackers compromised hosting servers. A single compromised server could host multiple legitimate websites, allowing malicious behavior to affect visitors to more than one site.
Reports described two parts of the compromise: a backdoor associated with the server’s SSH daemon (SSHD), and rogue Apache modules that altered what some website visitors received. The pages could still look normal to site owners and ordinary visitors.
How did Darkleech affect Apache websites?
- Compromise the server: The attackers gained server-level access. The initial route was not established in the contemporaneous reporting; weak credentials, social engineering, and vulnerable administration software were raised as possibilities, not confirmed causes.
- Establish access through SSHD: Reports described a malicious SSH daemon or backdoor. In a January 2013 Ars Technica report about SSH binary modifications, Sucuri CTO Daniel Cid said: “The modifications not only allow them to remote into the server bypassing existing authentication controls, but also allow them to steal all SSH authentications and push it to their remote servers.” That quotation concerns SSH binary modifications and should not be taken to mean every Darkleech incident used an identical method.
- Alter Apache behavior: The attackers uploaded or configured rogue Apache modules. Those modules could inject iframes dynamically, rather than leaving obvious malicious code in a website’s stored page files.
- Redirect selected visitors: The injected iframe could direct some visitors toward exploit-kit malware. Delivery was conditional, so a page might appear harmless during a routine check while exposing other visitors to malicious content.
SecurityWeek’s April 2013 account, citing Cisco researcher Mary Landesman, described the iframes as generated in real time, making them difficult to find and remove. That behavior also explains why viewing a page once or checking its static source was not enough to rule out a server compromise.
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Did Darkleech really infect 20,000 websites?
About 20,000 was Cisco’s estimate, not a site-by-site tally. Ars Technica reported that Cisco researchers had observed almost 2,000 compromised hosting servers between February and the first half of March 2013, across 48 countries. Cisco estimated the number of affected websites by assuming each server hosted about 10 sites.
Other reported figures describe different samples and should not be confused with that estimate:
| Figure | What it represents |
|---|---|
| About 20,000 websites | Cisco’s 2013 extrapolation from observed compromised servers using an assumption of about 10 hosted sites per server; not a verified count of unique infected sites. |
| Almost 2,000 servers | Compromised hosting servers observed by Cisco researchers from February through the first half of March 2013, across 48 countries. |
| 1,239 websites | A random sample reported by Cisco researchers; all sampled sites ran Apache 2.2.22 or higher. This sample does not establish that every infected site used those versions. |
| More than 40,000 domains and IP addresses; 15,000 active concurrently | ESET’s figures for the related Home campaign, which used a modified Darkleech variant: more than 40,000 domains and IP addresses appeared in rotation, with 15,000 active at the same time in May 2013. These are rotation-infrastructure figures, not a revised count of affected websites. |
What could website owners look for?
In the 2013 reports, a suspicious redirect URL sometimes contained an IP address followed by a hexadecimal component and q.php. That pattern was a clue, not proof: its presence alone would not establish a Darkleech infection, and its absence would not rule one out.
Because the malicious iframe could be generated by an Apache module in real time, the website’s saved files might not contain the injected code. The relevant investigation was at the server level: administrators were advised to review Apache’s configuration for unexpected modules and look for the associated SSH backdoor as well. Removing an injected module alone could leave the server-level access mechanism in place.
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These are observations about the challenges administrators faced in 2013, not current incident-response instructions. For a suspected compromise today, use current guidance from your hosting provider and qualified incident-response professionals; the historical reports do not establish current commands or product recommendations.
Were all related Apache attacks Darkleech?
No. The 2013 reporting described developments and other Apache activity that should not automatically be attributed to Darkleech.
- cPanel Apache binary replacement: In April 2013, Sucuri described attackers replacing the Apache
httpdbinary on cPanel-based servers. Sucuri noted that package-manager checks used to spot altered modules would not directly detect that replacement in cPanel’s custom Apache installation. This was a reported related development, not evidence that every Darkleech infection replaced the binary. - Home campaign: ESET reported a modified Darkleech variant in a campaign using URL-rotation infrastructure associated with compromised cPanel and Plesk servers. Its domain and IP figures describe infrastructure in rotation, not a direct count of infected websites.
- Uncertain module attribution: In June 2013, Sucuri described another Apache module injection but said it was unknown whether it was an improved Darkleech or a different tool. It should not be labelled definitively as Darkleech.
Is Darkleech still active?
The cited reporting documents activity and related investigations in 2013. It does not establish whether Darkleech is active today, how prevalent it may be, or whether modern incidents using similar techniques are connected to that campaign. The historical figures should not be read as current threat statistics.
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Sources
- SecurityWeek: Cisco: Darkleech Compromises 20,000 Websites (April 4, 2013)
- Ars Technica: Hackers infect 20,000 sites in one of the largest mass injections ever (April 2, 2013)
- Sucuri: Darkleech on cPanel Servers Replacing httpd Binary (April 26, 2013)
- ESET WeLiveSecurity: Operation Windigo: The vivisection of a large Linux server-side credential stealing operation (July 2, 2013)
- Cisco Blogs: Darkleech malware compromises web servers to infect visitors (April 2013)
- Sucuri: New Apache Module Injection Attack (June 20, 2013)
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