Criminals are sending malicious emails that purport to come from payroll services firms in order to infect with malware the computers of payroll administrators from various companies, according to researchers from the SANS Internet Storm Center (ISC).
"For the past couple of weeks, companies that offer outsourced payroll management services have seen their name being abused for phishing scams," SANS incident handler Daniel Wesemann said Sunday in a blog post.
"One prominent example is ADP, whose website currently alerts their customers to four different samples of phishing emails that make the rounds and claim to be from ADP," Wesemann said.
Automatic Data Processing (ADP) is an U.S.-based provider of outsourced business services, including payroll management, that claims to have approximately 600,000 clients.
In the most recent attack, criminals sent out rogue emails to ADP's customers claiming that the digital certificates they use to access the company's Internet services were about to expire.
The email recipients were asked to renew their certificates by clicking on a link that appeared to lead to ADP's website. However, the link directed users to an attack site that tried to exploit vulnerabilities in outdated browser plug-ins in order to infect their computers with malware, Wesemann said.
One of the exploits targeted a Java vulnerability identified as CVE-2012-1723 that was patched by Oracle in June. According to Jeong Wook Oh, a researcher with the Microsoft Malware Protection Center, Web-based attacks are increasingly targeting this flaw.
The CVE-2012-1723 exploit used in the ADP attack has a low detection rate on VirusTotal, an online file scanning service that uses 41 antivirus engines, Wesemann said. "The main reason for this seems to be that the exploit packs are encoded."
"ADP's Global Security Organization has received numerous reports regarding fraudulent emails referring to 'ADP Generated Message: First Notice - Digital Certificate Expiration'," ADP said in a security alert posted on its website on July 29. "ADP is working with our security vendors and fraud prevention team to identify and contain the source(s) of these emails."
The most recent date when the company received reports about such emails was August 2. "Please be on the lookout for variations of this fraudulent email," ADP said.
Sage, an UK-based payroll outsourcing provider, said via email that it has not received any reports about similar email-based attacks targeting its own customers.
"If you have an outsourced payroll provider, acquaint yourself with the email logs, so that you know how REAL email coming from this provider looks like," Wesemann said. "This knowledge is priceless during an incident, and might even help you to automatically block some of the more egregious phishes."
Wesemann also advised companies to remind their human resources and payroll management staff not to click on links in unsolicited email without verifying their authenticity first. "They are your first line of defense, and - given Antivirus' ineffectiveness - usually even your ONLY line of defense."