CVE-2013-2551
Microsoft Internet Explorer Use-After-Free Vulnerability
Description
CVE-2013-2551 is a use-after-free vulnerability in Microsoft Internet Explorer versions 6 through 10 that allows remote attackers to execute arbitrary code via a specially crafted web page. The flaw resides in the VML (Vector Markup Language) rendering engine, where an object in memory can be freed prematurely and then reused by attacker-controlled data. With an EPSS score of 97.3% (99.9th percentile), this vulnerability is among the most exploited browser flaws ever documented. CISA added CVE-2013-2551 to the Known Exploited Vulnerabilities catalog, confirming active exploitation in real-world attacks.
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 | internet explorer | 6; 7; 8; 9; 10 |
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://h30499.www3.hp.com/t5/HP-Security-Research-Blog/Pwn2Own-2013/ba-p/5981157(Broken Link, Third Party Advisory)
- http://twitter.com/VUPEN/statuses/309479075385327617(Broken Link)
- http://twitter.com/thezdi/statuses/309452625173176320(Not Applicable)
- http://www.us-cert.gov/ncas/alerts/TA13-134A(Third Party Advisory, US Government Resource)
- https://docs.microsoft.com/en-us/security-updates/securitybulletins/2013/ms13-037(Patch, Vendor Advisory)
- https://oval.cisecurity.org/repository/search/definition/oval%3Aorg.mitre.oval%3Adef%3A16317(Broken Link)
- https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2013-2551(US Government Resource)
Weakness Type
CWE-416: Use After Free
CVE-2013-2551 is caused by a use-after-free condition in Internet Explorer's VML rendering engine. When processing specially crafted VML content, the browser frees a memory object prematurely, but subsequent operations continue to reference the freed memory, allowing an attacker to overwrite it with malicious data and gain control of execution flow.
Learn more: CWE-416 — Use After Free
Impact Analysis
CVE-2013-2551 has a CVSS v2 base score of 9.3 (Critical), reflecting the severe consequences of successful exploitation. The vulnerability is exploitable remotely through a web browser with no authentication required — an attacker merely needs to lure a victim to a malicious or compromised website. Successful exploitation grants the attacker complete control over the affected system with the privileges of the logged-in user. The EPSS score of 97.3% (99.9th percentile) confirms that this vulnerability is among the most frequently exploited in the wild. Organizations still running legacy Internet Explorer versions face significant risk of drive-by download attacks leveraging this flaw.
Exploit Maturity
Public exploit code for CVE-2013-2551 has been widely available since its disclosure in 2013, and multiple exploit kits have incorporated this vulnerability into their arsenals. The vulnerability was notably used in targeted attacks and was demonstrated at the Pwn2Own 2013 competition. CISA confirmed active exploitation by adding it to the KEV catalog. The EPSS score of 97.3% (99.9th percentile) reflects near-universal exploitation activity across the threat landscape.
Remediation
- Apply Microsoft security update MS13-037 which addresses the use-after-free vulnerability in Internet Explorer's VML rendering engine. Ensure all Internet Explorer installations across the organization are updated to the patched version.
- Migrate away from Internet Explorer to a modern, supported browser such as Microsoft Edge, Google Chrome, or Mozilla Firefox. Internet Explorer has reached end of life and no longer receives security updates.
- Implement network-level protections including web filtering and intrusion prevention systems (IPS) with signatures for known IE exploit patterns to detect and block exploitation attempts targeting legacy browser installations.
- Enable Enhanced Protected Mode in Internet Explorer where migration is not immediately possible, and ensure users operate with least-privilege accounts to limit the impact of successful exploitation.
- Conduct an asset inventory to identify all systems still running Internet Explorer and prioritize their migration or isolation from untrusted web content.
Technical Details
CVE-2013-2551 exploits a use-after-free vulnerability (CWE-416) in Microsoft Internet Explorer's handling of VML (Vector Markup Language) objects. The flaw occurs in the processing of the VGX.DLL library, where a VML shape element's stroke property can trigger premature deallocation of a memory object. When the rendering engine subsequently attempts to access this freed object during layout recalculation, the attacker can control the contents of the reallocated memory region. By crafting specific VML content with manipulated stroke dash-style arrays, an attacker achieves arbitrary code execution in the context of the browser process. The attack requires no plugins beyond the built-in VML support present in all affected IE versions (6 through 10).
Frequently Asked Questions
Is CVE-2013-2551 being actively exploited?
Yes, CVE-2013-2551 has been extensively exploited in the wild since 2013. CISA confirmed active exploitation by including it in the Known Exploited Vulnerabilities catalog. Multiple exploit kits incorporated this vulnerability, and the EPSS score of 97.3% places it among the most exploited browser vulnerabilities ever documented.
What products are affected by CVE-2013-2551?
Microsoft Internet Explorer versions 6, 7, 8, 9, and 10 running on all supported Windows operating systems are affected. The vulnerability resides in the VGX.DLL component responsible for VML rendering, which is present in all affected IE versions.
How do I fix CVE-2013-2551?
Apply Microsoft security update MS13-037. However, since Internet Explorer has reached end of life, the recommended approach is to migrate to a modern browser such as Microsoft Edge, Chrome, or Firefox. If legacy IE is still required, isolate those systems from untrusted web content.
How severe is CVE-2013-2551?
CVE-2013-2551 has a CVSS v2 score of 9.3 (Critical) and enables full remote code execution through a simple visit to a malicious web page. No user interaction beyond visiting the page is required. The EPSS score of 97.3% confirms it remains one of the most dangerous browser vulnerabilities.
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