CVE-2016-0034 in Silverlight
Summary
by MITRE
Microsoft Silverlight 5 before 5.1.41212.0 mishandles negative offsets during decoding, which allows remote attackers to execute arbitrary code or cause a denial of service (object-header corruption) via a crafted web site, aka "Silverlight Runtime Remote Code Execution Vulnerability."
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Analysis
by VulDB Data Team • 04/23/2026
Microsoft Silverlight 5 before 5.1.41212.0 contains a critical vulnerability in its media decoding component that stems from improper handling of negative offsets during content processing. This flaw exists within the runtime environment's object header management system where negative offset values are not properly validated or sanitized before being processed. The vulnerability falls under the category of improper input validation and memory corruption issues, specifically aligning with CWE-129 and CWE-787 which address issues related to insufficient validation of length values and out-of-bounds writes. Attackers can exploit this weakness by crafting malicious web content that includes specially formatted media files or data structures with negative offset values that cause the Silverlight runtime to corrupt object headers in memory. The exploitation occurs when the runtime attempts to decode media content and processes these malformed offset values, leading to unpredictable memory behavior that can be leveraged for remote code execution.
The operational impact of this vulnerability extends beyond simple denial of service scenarios to include full system compromise capabilities. When a user visits a malicious website hosting crafted Silverlight content, the runtime environment becomes vulnerable to arbitrary code execution through memory corruption techniques that can bypass standard security measures. The object-header corruption aspect means that the memory layout of critical runtime structures becomes corrupted, potentially allowing attackers to overwrite function pointers, control registers, or other essential runtime components. This vulnerability specifically targets the Silverlight runtime's media decoding pipeline, making it particularly dangerous in environments where Silverlight applications are frequently used for rich media content delivery. The attack vector through web-based content makes this vulnerability highly exploitable in typical user environments where browsing activity is common.
The exploitation of CVE-2016-0034 aligns with several tactics described in the MITRE ATT&CK framework, particularly those related to initial access through malicious websites and privilege escalation via code execution. The vulnerability can be classified under ATT&CK technique T1203 (Exploitation for Client Execution) and T1059 (Command and Scripting Interpreter) as attackers can leverage the runtime execution environment to deploy malicious payloads. Organizations running Silverlight applications face significant risk as this vulnerability can be exploited through standard web browsing activities without requiring any special user interaction beyond visiting a compromised website. The vulnerability's impact is compounded by the widespread deployment of Silverlight in enterprise environments, making it a prime target for attackers seeking to gain persistent access to corporate networks through browser-based attacks.
Mitigation strategies for this vulnerability require immediate patching of Silverlight runtime installations to version 5.1.41212.0 or later, which includes proper validation of offset values during media decoding operations. System administrators should implement browser security policies that disable Silverlight plugins where possible and ensure that all Silverlight content is served from trusted sources only. Network-based mitigations can include web application firewalls that detect and block malicious Silverlight content patterns, though these solutions may not prevent all exploitation attempts. Organizations should also consider implementing runtime monitoring solutions that can detect anomalous memory access patterns or object header corruption behaviors indicative of exploitation attempts. The vulnerability highlights the importance of proper input validation and memory safety practices in runtime environments, particularly for technologies that process untrusted media content. Regular security assessments should include evaluation of legacy technologies like Silverlight that may contain unpatched vulnerabilities, as these systems often remain operational despite known security risks.