A remote code execution vulnerability exists when Microsoft Silverlight improperly allows applications to access objects in memory. The vulnerability could corrupt system memory, which could allow an attacker to execute arbitrary code. In a web-browsing scenario, an attacker who successfully exploited this vulnerability could obtain the same permissions as the currently logged-on user. If a user is logged on with administrative user rights, an attacker could take complete control of the affected system. An attacker could then install programs; view, change, or delete data; or create new accounts with full user rights. Users whose accounts are configured to have fewer user rights on the system could be less impacted than users who operate with administrative user rights.
To exploit the vulnerability, an attacker could host a website that contains a specially crafted Silverlight application and then convince a user to visit the compromised website. The attacker could also take advantage of websites containing specially crafted content, including those that accept or host user-provided content or advertisements. For example, an attacker could display specially crafted web content by using banner advertisements or by using other methods to deliver web content to affected systems. However, in all cases, an attacker would have no way to force a user to visit a compromised website. Instead, an attacker would have to convince a user to visit the website, typically by enticing the user to click a link in either an email or instant message.
The update addresses the vulnerability by correcting how Microsoft Silverlight allocates memory for inserting and appending strings in StringBuilder.
## Where it's fixed | Platform | Product | Fixed in | Fix | Released | |---|---|---|---|---| | Microsoft | Microsoft Silverlight 5 Developer Runtime when installed on Apple Mac OS (Intel-based) | | [KB3182373](https://patchblox.com/security/data/fix/microsoft/kb3182373.md) | Sep 13, 2016 | | Microsoft | Microsoft Silverlight 5 Developer Runtime when installed on Microsoft Windows (32-bit) | | [KB3182373](https://patchblox.com/security/data/fix/microsoft/kb3182373.md) | Sep 13, 2016 | | Microsoft | Microsoft Silverlight 5 Developer Runtime when installed on Microsoft Windows (x64-based) | | [KB3182373](https://patchblox.com/security/data/fix/microsoft/kb3182373.md) | Sep 13, 2016 | | Microsoft | Microsoft Silverlight 5 when installed on Apple Mac OS (Intel-based) | | [KB3182373](https://patchblox.com/security/data/fix/microsoft/kb3182373.md) | Sep 13, 2016 | | Microsoft | Microsoft Silverlight 5 when installed on Microsoft Windows (32-bit) | | [KB3182373](https://patchblox.com/security/data/fix/microsoft/kb3182373.md) | Sep 13, 2016 | | Microsoft | Microsoft Silverlight 5 when installed on Microsoft Windows (x64-based) | | [KB3182373](https://patchblox.com/security/data/fix/microsoft/kb3182373.md) | Sep 13, 2016 | --- Data as of 2026-11-11T19:49:26Z UTC. Source: Patchblox Patch Radar (https://patchblox.com/security/patch-radar). Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo Free to use with attribution: show "Data: Patchblox Patch Radar" with a link to https://patchblox.com/security/patch-radar. Terms, including what needs a written agreement: https://patchblox.com/security/patch-radar/use-the-data Product names, logos and trademarks shown on Patch Radar belong to their respective owners. They are used only to identify the software each security fix applies to and to help readers find their platform. Their use does not imply any affiliation with, or endorsement by, those owners, and Patchblox is not affiliated with any of them.