--- title: Hackers Use VoIP Systems To Install PHP Web Shells description: Hackers Use VoIP Systems To Install PHP Web Shells --- [Securafy Knowledge Hub](https://blog.securafy.com) - [Topics](https://blog.securafy.com/#sf-cover) - [Tools](https://blog.securafy.com/#sf-tools) - [Books & Guides](https://blog.securafy.com/#sf-books) [Talk to Securafy](https://meetings.hubspot.com/securafy/strategy-call) [Topics](https://blog.securafy.com/#sf-cover) [Tools](https://blog.securafy.com/#sf-tools) [Books & Guides](https://blog.securafy.com/#sf-books) [Talk to Securafy](https://meetings.hubspot.com/securafy/strategy-call) [Knowledge Hub](https://blog.securafy.com) / IT Operations IT Operations # Hackers Use VoIP Systems To Install PHP Web Shells Hackers Use VoIP Systems To Install PHP Web Shells ![Randy Hall](https://blog.securafy.com/hubfs/Randy%20Hall%202.png) By Randy Hall Updated Jul 2024 2 min read Share [**](https://www.linkedin.com/sharing/share-offsite/?url=https://blog.securafy.com/2022/08/22/hackers-use-voip-systems-to-install-php-web-shells) [**](https://twitter.com/intent/tweet?url=https://blog.securafy.com/2022/08/22/hackers-use-voip-systems-to-install-php-web-shells&text=%3Cspan+id%3D%22hs_cos_wrapper_name%22+class%3D%22hs_cos_wrapper+hs_cos_wrapper_meta_field+hs_cos_wrapper_type_text%22+style%3D%22%22+data-hs-cos-general-type%3D%22meta_field%22+data-hs-cos-type%3D%22text%22+%3EHackers+Use+VoIP+Systems+To+Install+PHP+Web+Shells%3C%2Fspan%3E) [**](mailto:?subject=%3Cspan+id%3D%22hs_cos_wrapper_name%22+class%3D%22hs_cos_wrapper+hs_cos_wrapper_meta_field+hs_cos_wrapper_type_text%22+style%3D%22%22+data-hs-cos-general-type%3D%22meta_field%22+data-hs-cos-type%3D%22text%22+%3EHackers+Use+VoIP+Systems+To+Install+PHP+Web+Shells%3C%2Fspan%3E&body=https://blog.securafy.com/2022/08/22/hackers-use-voip-systems-to-install-php-web-shells) ![](https://static.hsstatic.net/BlogImporterAssetsUI/ex/missing-image.png)Security researchers at Unit 42, a division of Palo Alto Networks, have been tracking the efforts of a massive campaign aimed at Elastix VoIP telephony servers. They are used by companies of all shapes and sizes to unify their communications, and it is especially attractive because it can be used with the Digium phones module for FreePBX. So far, the team has collected more than half a million malicious code samples over a three-month period.  An analysis of those code samples reveals that the attackers are exploiting a remote code execution vulnerability. It is being tracked as CVE-2021-4561 and carries a severity rating of 9.8 out of ten. Security researchers report that hackers have been actively exploiting this flaw since at least December 2021. Based on the code samples collected, the Unit 42 team believes that the attackers' goal was to plant PHP web shells on successfully penetrated systems. That would allow them to execute arbitrary commands on the compromised servers. Another security firm, Check Point, confirms Unit 42's findings and both teams stress that the campaign is still ongoing.  Worse, it appears that there are two different groups involved in the attack. Although it is not currently known whether they are coordinating their efforts or if that fact is coincidental. Perhaps it is a case of one following the other so as not to miss out on an opportunity. The attackers behind the campaign are both clever and technically savvy.  They've built in some good anti-detection strategies into the attack, such as masking the name of the back door so that the file name resembles that of a known file already on the system.  It would take a sharp pair of eyes indeed to spot it. In any event, if you use Elastix VoIP, be sure your IT people are aware of this threat. Tagged Under IT Operations[Cybersecurity](https://blog.securafy.com/tag/cybersecurity)Business Continuity In This Article Need Help With Your Current Setup? Talk through your current systems, risks, and support gaps with Securafy. [Book a Strategy Call](https://meetings.hubspot.com/securafy/strategy-call) ## Join The Conversation Have a question or perspective on this topic? Add it below. ![Randy Hall](https://blog.securafy.com/hubfs/Randy%20Hall%202.png) About The Author Randy Hall · CEO & Founder Randy Hall is the CEO and Founder of Securafy, with decades of experience helping organizations make smarter, safer decisions about technology. A frequent speaker and instructor at national IT events, Randy has advised thousands of organizations, from startups and SMBs to large enterprises and U.S. government entities, on secure, practical technology adoption. He writes about the decisions business leaders are often expected to make without enough context, including cybersecurity, compliance, AI, cyber insurance, IT strategy, and business resilience. Outside the office, you’ll often find Randy on Lake Erie enjoying time on his 38-foot Chris-Craft. **Writes about:** Cybersecurity strategy, compliance, AI security, business resilience, cyber insurance, SMB risk, IT leadership [More From This Author →](https://blog.securafy.com/author/randyhall) Related Articles Business Continuity [Compliance Risk Assessment: How Downtime Impacts Your Bottom Line](https://blog.securafy.com/compliance-risk-assessment-how-downtime-impacts-your-bottom-line) When systems go down, compliance obligations don't pause—and the financial consequences ... Jul 28, 2026 Compliance [HIPAA Security Rule Changes Are Delayed To 2027: Why Healthcare Organizations Should Not Wait](https://blog.securafy.com/hipaa-security-rule-changes-are-delayed-to-2027-why-healthcare-organizations-should-not-wait) The updated HIPAA Security Rule won't take effect until 2027, but healthcare ... 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