Researcher finds major flaw in Facebook

The issue could allow hackers to send malicious software to people who aren't their friends

A security penetration tester discovered a major flaw in Facebook that could allow a person to send anyone on the social-networking site malicious applications.

Nathan Power, a senior security penetration tester at technology consultancy CDW, discovered the vulnerability and publicly disclosed it Thursday on his blog. The flaw was reported to Facebook on Sept. 30, which acknowledged the issue on Wednesday, he wrote.

Power, who could not immediately be reached, wrote that Facebook does not normally allow a person to send an executable attachment using the "Message" tab. If you try to do that, it returns the message "Error Uploading: You cannot attach files of that type."

Power wrote that an analysis of the browser's "POST" request sent to Facebook's servers showed that a variable called "filename" is parsed to see if a file should be allowed. But by simply by modifying the POST request with a space just after the file name, an executable could be attached to the message.

"This was enough to trick the parser and allow our executable file to be attached and sent in a message," Power wrote.

A person would not have to be an approved friend of the sender, as Facebook allows people to send those who are not their friends messages. The danger is that a hacker could use social engineering techniques to coax someone to launched the attachment, which could potentially infect their computer with malicious software.

Facebook representatives contacted in London did not have an immediate response on Thursday afternoon.

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