Security Experts:

Exploit for Recently Patched Silverlight Flaw Added to Angler

The French security researcher known as “Kafeine” revealed on Tuesday that an exploit for a recently patched Microsoft Silverlight vulnerability has been added to the Angler exploit kit.

Kafeine noticed on February 18 that Angler authors had added code for the integration of a Silverlight exploit. On Monday, the expert discovered that the integration of the Silverlight exploit had been completed and that the vulnerability leveraged by the attackers was CVE-2016-0034, which Microsoft patched in January with the release of security bulletin MS16-006.

Kaspersky malware analyst Anton Ivanov and others have confirmed that an exploit for CVE-2016-0034 has been indeed added to Angler.

In one of the tests performed by Kafeine, the Silverlight exploit had been used to deliver a variant of the TeslaCrypt ransomware. The researcher has confirmed that the attack does not work if Silverlight 5.1.41212.0, the version released by Microsoft to patch the vulnerability, is installed on the system.

The Silverlight vulnerability was discovered in late November by researchers at Kaspersky based on a YARA rule designed to detect an exploit that a Russian hacker had offered to sell to Italian spyware maker Hacking Team in 2013.

The hundreds of gigabytes of Hacking Team data leaked by a hacker in July 2015 included emails exchanged by the company with people offering to sell exploits. In 2013, a Russian exploit developer named Vitaliy Toropov offered to sell Hacking Team a Silverlight exploit.

While it’s unclear if Hacking Team actually acquired the Silverlight exploit from Toropov, Kaspersky researchers created a YARA rule based on the Russian hacker’s publicly available code in an effort to track down the exploit he had attempted to sell to the Italian company.

The YARA rule helped experts discover a sample on a user’s machine and on a multiscanner service. An analysis revealed that it was a new Silverlight exploit.

It’s not uncommon for Angler developers to add exploits for recently patched vulnerabilities to their creation, and in many cases it takes them only a few days to do it. For instance, an exploit for a Flash Player heap buffer overflow vulnerability (CVE-2015-8446) patched by Adobe on December 8 was added to Angler on December 14. Malwarebytes reported that the exploit had been used to deliver TeslaCrypt ransomware.

Related: CryptoWall 4.0 Spreading via Angler Exploit Kit

Related: Exploit Kits Mutate, Increase Activity

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Eduard Kovacs (@EduardKovacs) is a contributing editor at SecurityWeek. He worked as a high school IT teacher for two years before starting a career in journalism as Softpedia’s security news reporter. Eduard holds a bachelor’s degree in industrial informatics and a master’s degree in computer techniques applied in electrical engineering.