informa
News

Hackers Offer Free Porn To Beat Security Checks

Spammers are enticing consumers with free porn or games in exchange for help cracking CAPTCHAs on targeted websites, security researchers say.
Accordingly, any website that relies on Captchas shouldn't make that its only defense against automated attacks or spammers. "Human-based Captcha solving services pose a serious threat to Web security and challenge the whole concept of Captchas," said the report. "They were originally intended to distinguish humans from computers, but now automated software is using actual humans to cheat the test and pass as humans."

For example, Imperva said that it reviewed a Captcha-defeating attack against a Brazilian government agency and saw what appeared to be an attack tool continually requesting refreshes of the security page containing a Captcha challenge. "It seems that the attack tool 'pressed' this button to gather more and more Captcha images, perhaps to create an offline dictionary for future use," said the report. With such a dictionary, the attack tool could take a screenshot of every Captcha, compare it with a dictionary of Captcha images that had been "solved" by humans, and then successfully bypass the Captcha security check.

Another attack detailed by Imperva was made against a Brazilian government agency that handles tax administration, validates the country's social security numbers, and also provides financial information for companies. Documents from this agency are required as a pre-condition to many other services in Brazil, like issuing a passport or getting a loan, according to the report.

To protect the site, the agency uses Captchas, as well as a rate limit, source IP limit--limiting the frequency of connections allowed from a given IP address range--and some other limitations to avoid a denial of service and automated access. But many corporate users--the report cites loan companies, banks, accounting offices, and law firms--actually purchase third-party software to bypass the Captchas and other security mechanisms to help them more rapidly access information about their customers.

Fortunately, attempts to automatically gather Captcha information or defeat such systems can leave telltale signs. For example, these requests often sport unusual rates of access--all originating from the same IP address--or use unusual HTTP headers. Accordingly, these techniques can be identified and used to block or throttle requests from suspect IP addresses. Blacklisting known bad sites and tracking reputation can also be employed to help identify which requests to block outright.

Imperva's report also recommends creating a baseline of normal behavior. "A site can create a profile of legitimate use in terms of rate of access, requested URLs, distribution, traffic volume, geo-location--[an] IP from [the] Ukraine trying to post in a Japanese blog," then require any user exhibiting suspicious behavior to jump through additional security hoops. As with other security tools, in other words, Captchas work best as part of a layered defense.

Security information and event monitoring technology has been available for years, but the information can be hard to mine. In our SIEM Success report, we provide a step-by-step guide to make the most of your SIEM system. (Free registration required.)

Recommended Reading: