WebGL Considered Harmful
The Khronos Group’s WebGL technology is a cross-platform, low-level 3D graphics API for the web. Recently, Context Information Security published two reports critical of the WebGL technology, WebGL – A New Dimension for Browser Exploitation and WebGL – More WebGL Security Flaws.
One of the functions of MSRC Engineering is to analyze various technologies in order to understand how they can potentially affect Microsoft products and customers. As part of this charter, we recently took a look at WebGL. Our analysis has led us to conclude that Microsoft products supporting WebGL would have difficulty passing Microsoft’s Security Development Lifecycle requirements. Some key concerns include:
The security of WebGL as a whole depends on lower levels of the system, including OEM drivers, upholding security guarantees they never really need to worry about before. Attacks that may have previously resulted only in local elevation of privilege may now result in remote compromise. While it may be possible to mitigate these risks to some extent, the large attack surface exposed by WebGL remains a concern. We expect to see bugs that exist only on certain platforms or with certain video cards, potentially facilitating targeted attacks.
- Browser support for WebGL directly exposes hardware functionality to the web in a way that we consider to be overly permissive
As WebGL vulnerabilities are uncovered, they will not always manifest in the WebGL API itself. The problems may exist in the various OEM and system components delivered by IHV’s. While it has been suggested that WebGL implementations may block the use of affected hardware configurations, this strategy does not seem to have been successfully put into use to address existing vulnerabilities.
- Browser support for WebGL security servicing responsibility relies too heavily on third parties to secure the web experience
It is our belief that as configurations are blocked, increasing levels of customer disruption may occur. Without an efficient security servicing model for video card drivers (eg: Windows Update), users may either choose to override the protection in order to use WebGL on their hardware, or remain insecure if a vulnerable configuration is not properly disabled. Users are not accustomed to ensuring they are up-to-date on the latest graphics card drivers, as would be required for them to have a secure web experience. In some cases where OEM graphics products are included with PCs, retail drivers are blocked from installing. OEMs often only update their drivers once per year, a reality that is just not compatible with the needs of a security update process.
Modern operating systems and graphics infrastructure were never designed to fully defend against attacker-supplied shaders and geometry. Although mitigatinos such as ARB_robustness and the forthcoming ARB_robustness_2 may help, they have not proven themselves capable of comprehensively addressing the DoS threat. While traditionally client-side DoS is not a high severity threat, if this problem is not addressed holistically it will be possible for any web site to freeze or reboot systems at will. This is an issue for some important usage scenarios such as in critical infrastructure.
- Problematic system DoS scenarios
We believe that WebGL will likely become an ongoing source of hard-to-fix vulnerabilities. In its current form, WebGL is not a technology Microsoft can endorse from a security perspective.
We recognize the need to provide solutions in this space however it is our goal that all such solutions are secure by design, secure by default, and secure in deployment.
- MSRC Engineering
Expect Mozilla/Google fire back on this topic soon