As of July 1, all personal computers sold in China must be pre-installed with content filtering software called Green Dam. The officially stated goal is to protect children from online pornography, but naturally, the technology will also serve to "protect" viewers from offensive text and images such as politically sensitive content. Subsequent to this announcement, researchers at the University of Michigan have published a report detailing several remotely exploitable vulnerabilities in the Green Dam software. These vulnerabilities include:

  • Stack buffer overflow in URL blacklisting code due to a fixed-length buffer, triggered by URLs longer than approximately 2064 characters
  • Stack buffer overflow in filter file parsing due to a fixed-length buffer used in a call to fscanf()

In addition, the Michigan team noted that the software fails to encrypt or authenticate the filter auto-update process, and the use of unsafe string processing functions is systemic, meaning that other exploitable vulnerabilities may be lurking just beneath the surface.


Upon learning of these vulnerabilities, the Chinese government ordered Green Dam to fix the security holes immediately. But even with those hastily applied patches, it seems likely that the software is probably riddled with additional flaws. In downplaying the severity of the entire matter, Green Dam implies that their development process probably doesn't include independent, third-party security assessments. If quick fixes of the most severe issues are sufficient to appease the government, that is probably all they will do.

Ironically, by attempting to "protect" Chinese citizens from online content, the government is doing exactly the opposite by reducing the security posture of those PCs and homogenizing the attack surface. You can just envision all the foreign governments and botnet operators rubbing their hands together with glee as they prepare to fuzz Green Dam for some 0-day exploits. The government wants to be perceived as caring about Internet safety (hence the public insistence on the bug fixes) but in reality they are adding a weak link to the chain.

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About Chris Eng

Chris Eng, vice president of research, is responsible for integrating security expertise into Veracode’s technology. In addition to helping define and prioritize the security feature set of the Veracode service, he consults frequently with customers to discuss and advance their application security initiatives. With over 15 years of experience in application security, Chris brings a wealth of practical expertise to Veracode.

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