CVE-2016-0034
Microsoft Silverlight Runtime Remote Code Execution Vulnerability
Description
CVE-2016-0034 is a remote code execution vulnerability in Microsoft Silverlight caused by improper handling of negative offsets during decoding operations. An attacker can exploit this flaw to execute arbitrary code or cause a denial-of-service condition on the affected system. The vulnerability is triggered when Silverlight processes specially crafted content, which can be delivered through malicious web pages. CISA has listed CVE-2016-0034 in the Known Exploited Vulnerabilities catalog with confirmed ransomware association, and its EPSS percentile of 97.3% indicates a very high probability of exploitation. The impacted product is end-of-life and should be disconnected if still in use.
KEV Information
CVSS Score
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:HOpen in CalculatorAffected Products
| Vendor | Product | Version |
|---|---|---|
| microsoft | silverlight | >= 5.0, < 5.1.41212.0 |
Multiple CVSS Assessments
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
References
- http://www.securitytracker.com/id/1034655(Broken Link, Third Party Advisory, VDB Entry)
- https://docs.microsoft.com/en-us/security-updates/securitybulletins/2016/ms16-006(Patch, Vendor Advisory)
- https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2016-0034(US Government Resource)
Weakness Type
No specific CWE has been assigned to CVE-2016-0034 in the NVD database. The vulnerability involves improper handling of negative offsets during decoding in Microsoft Silverlight. When the Silverlight runtime decodes crafted content, negative offset values cause the decoder to access memory outside intended boundaries, leading to memory corruption. This weakness relates to improper input validation of offset values in binary content processing, enabling both code execution and denial-of-service outcomes.
Learn more: CWE Overview
Impact Analysis
CVE-2016-0034 allows remote code execution or denial of service through Microsoft Silverlight's decoding operations. The vulnerability is remotely exploitable through specially crafted web content, requiring only that a user visits a page with malicious Silverlight content. Confidentiality (High): Successful code execution gives the attacker access to all data accessible by the Silverlight process and the browser, including session data, cached credentials, and local files. Integrity (High): Arbitrary code execution allows installation of persistent malware, system modification, and establishment of backdoor access. Availability (High): Beyond code execution, the vulnerability can also trigger denial-of-service conditions, crashing the Silverlight runtime or the hosting browser. CISA has confirmed ransomware association with CVE-2016-0034, and the EPSS percentile of 97.3% indicates a very high likelihood of active exploitation.
Exploit Maturity
CISA has confirmed active exploitation of CVE-2016-0034 and noted confirmed ransomware association, making this vulnerability particularly dangerous. The CISA-required action states that the impacted product is end-of-life and should be disconnected if still in use, with a remediation deadline of June 15, 2022. The EPSS percentile of 97.3% places this vulnerability among the most likely to be exploited. The ransomware association indicates that threat actors have incorporated this Silverlight vulnerability into attack chains for deploying ransomware payloads, leveraging the widespread historical deployment of Silverlight in enterprise environments.
Remediation
- Remove Microsoft Silverlight entirely from all systems. As stated in the CISA KEV required action, the impacted product is end-of-life and should be disconnected if still in use. Microsoft ended Silverlight support on October 12, 2021.
- Remove Silverlight browser plugins from all browsers across the organization. Modern browsers no longer support Silverlight, but legacy browsers may still have the plugin installed.
- Migrate Silverlight-dependent applications to modern web technologies. Replace internal applications built on Silverlight with HTML5, JavaScript, or Blazor-based alternatives. Identify all web applications that require Silverlight for functionality.
- Block Silverlight content at network boundaries using web proxies and content filtering to prevent delivery of malicious Silverlight (.xap) files, even on systems where Silverlight has not yet been removed.
- Monitor for indicators of ransomware activity given the confirmed ransomware association. Review endpoint detection logs for suspicious Silverlight-related process behavior, unexpected file encryption activity, or connections to known command-and-control infrastructure.
Technical Details
CVE-2016-0034 is a memory corruption vulnerability in Microsoft Silverlight's decoding engine. The flaw occurs when the decoder mishandles negative offset values during the processing of specially crafted content. Negative offsets cause the decoder to calculate incorrect memory addresses, reading from or writing to memory locations outside the intended buffer boundaries. This out-of-bounds memory access corrupts program state and can be leveraged to achieve arbitrary code execution. The Silverlight runtime processes content within a browser plugin context, meaning exploitation occurs when a user navigates to a page containing malicious Silverlight content. The vulnerability can result in either code execution (when the memory corruption is carefully controlled) or denial of service (when the corruption causes an unrecoverable crash), making it a dual-impact vulnerability.
Frequently Asked Questions
Is CVE-2016-0034 being actively exploited?
Yes, CVE-2016-0034 is actively exploited with confirmed ransomware association. CISA included it in the Known Exploited Vulnerabilities catalog and the impacted product is end-of-life. The EPSS percentile of 97.3% indicates very high exploitation probability.
What products are affected by CVE-2016-0034?
CVE-2016-0034 affects Microsoft Silverlight. The product reached end-of-life on October 12, 2021, and no longer receives security updates. Any remaining installations are permanently vulnerable to this and other unpatched vulnerabilities.
How do I fix CVE-2016-0034?
Completely remove Microsoft Silverlight from all systems and browsers. Since the product is end-of-life, no patches are available. Migrate Silverlight-dependent applications to modern web technologies and block Silverlight content at network boundaries.
How severe is CVE-2016-0034?
CVE-2016-0034 is a remote code execution vulnerability with confirmed ransomware association and an EPSS percentile of 97.3%. The combination of active exploitation, ransomware usage, and end-of-life status makes immediate removal of Silverlight critical for organizational security.
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