CVE-2013-3896

What is Microsoft Silverlight?

Microsoft Silverlight was a browser plugin for rich internet applications, serving a role similar to Adobe Flash. Silverlight 5 was the final major version; Microsoft ended mainstream support in 2012 and the plugin reached end-of-life in October 2021. During its active deployment period, Silverlight was installed on hundreds of millions of Windows systems and targeted by exploit kits alongside Flash and Java as a primary browser plugin attack surface.

Overview

CVE-2013-3896 is an information disclosure vulnerability in Microsoft Silverlight 5 caused by improper pointer validation when accessing Silverlight elements. A crafted Silverlight application can trigger the flaw to read data from unvalidated memory pointers, leaking process memory contents to the attacker. Though classified as information disclosure (no integrity or availability impact), memory content leaks of this type are commonly used as ASLR-bypass components in exploit chains, enabling follow-on code execution attacks.

Microsoft patched this in MS13-087 on October 8, 2013.

Affected Versions

Technical Details

Silverlight's runtime exposes a programmatic interface to Silverlight element objects through its managed API. The vulnerability occurs when Silverlight accesses element objects through unvalidated pointers — the runtime dereferences a pointer without verifying it points to valid memory in the correct range, allowing a malicious Silverlight application to read arbitrary data from the browser process's memory space.

Information disclosure as an exploit component: The CVSS confidentiality impact is High, reflecting that the disclosed memory contents can include sensitive data from the browser process. More importantly in the threat model of 2013, pointer leaks served as the mechanism to defeat ASLR (Address Space Layout Randomization):

• ASLR randomizes the base addresses of loaded modules at runtime
• An attacker exploiting a memory corruption bug needs a valid heap or stack address to reliably land their payload
• A controlled information leak that returns raw pointers provides those addresses, making ASLR effectively non-functional for the duration of the attack

Silverlight information disclosure vulnerabilities were particularly paired with Silverlight code execution bugs in exploit kits during 2012–2014.

Discovery

Discovered through security research and reported to Microsoft, resulting in inclusion in the October 2013 Patch Tuesday MS13-087.

Exploitation Context

CISA confirmed exploitation in the wild. Silverlight vulnerabilities were actively maintained in exploit kits including Angler and Neutrino through approximately 2016, after which Flash and Java dominance in exploit kit payloads faded as all three plugins declined in browser usage. CISA's 2022 addition to the KEV catalog indicates confirmed exploitation during the Silverlight deployment window.

Remediation

Microsoft Silverlight reached end-of-life on October 12, 2021. Organizations should:

1. Uninstall Silverlight from all endpoints — it is no longer needed for any current use case
2. Verify removal via endpoint management tools (look for sllauncher.exe and npctrl.dll)
3. Remove Silverlight plugin entries from all browsers
4. Block Silverlight content (.xap files) at web content filtering gateways
5. Any system still running Silverlight should be treated as fully unpatched for Silverlight CVEs since no further updates will be issued