CVE-2010-3962
Microsoft Internet Explorer Uninitialized Memory Corruption Vulnerability
Description
CVE-2010-3962 is a use-after-free vulnerability in Microsoft Internet Explorer versions 6, 7, and 8, allowing remote attackers to execute arbitrary code through crafted CSS token sequences and the clip attribute. Exploited in the wild since November 2010, this vulnerability was used in targeted attacks before a patch was available. With an EPSS score of 0.8703 (99.4th percentile), this vulnerability remains a significant threat and has been added to CISA's Known Exploited Vulnerabilities (KEV) catalog with a remediation deadline of October 27, 2025.
KEV Information
CVSS Score
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:HOpen in CalculatorAffected Products
| Vendor | Product | Version |
|---|---|---|
| microsoft | internet explorer | 6; 7; 8 |
References
- http://blogs.technet.com/b/msrc/archive/2010/11/02/microsoft-releases-security-advisory-2458511.aspx(Vendor Advisory)
- http://secunia.com/advisories/42091(Broken Link, Vendor Advisory)
- http://www.exploit-db.com/exploits/15418(Third Party Advisory, VDB Entry)
- http://www.exploit-db.com/exploits/15421(Third Party Advisory, VDB Entry)
- http://www.kb.cert.org/vuls/id/899748(Third Party Advisory, US Government Resource)
- http://www.microsoft.com/technet/security/advisory/2458511.mspx(Patch, Vendor Advisory)
- http://www.securityfocus.com/bid/44536(Broken Link, Third Party Advisory, VDB Entry)
- http://www.securitytracker.com/id?1024676(Broken Link, Third Party Advisory, VDB Entry)
- http://www.symantec.com/connect/blogs/new-ie-0-day-used-targeted-attacks(Not Applicable)
- http://www.us-cert.gov/cas/techalerts/TA10-348A.html(Third Party Advisory, US Government Resource)
- http://www.vupen.com/english/advisories/2010/2880(Broken Link, Vendor Advisory)
- https://docs.microsoft.com/en-us/security-updates/securitybulletins/2010/ms10-090(Patch, Vendor Advisory)
- https://exchange.xforce.ibmcloud.com/vulnerabilities/62962(Third Party Advisory, VDB Entry)
- https://oval.cisecurity.org/repository/search/definition/oval%3Aorg.mitre.oval%3Adef%3A12279(Tool Signature)
- https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2010-3962(US Government Resource)
Weakness Type
CWE-416: Use After Free
CWE-416 describes a condition where a program continues to use a pointer after the memory it references has been freed. In CVE-2010-3962, Internet Explorer's rendering engine frees a memory object related to CSS processing but subsequently accesses that freed memory through a dangling pointer when handling the clip attribute. This type of vulnerability is particularly dangerous in web browsers because an attacker can precisely control memory allocation patterns through JavaScript and HTML, enabling them to place attacker-controlled data in the freed memory location and hijack program execution.
Impact Analysis
The business impact of CVE-2010-3962 is substantial as it enables remote code execution through a web browser, one of the most commonly used applications in any organization. Confidentiality Impact is high because successful exploitation allows an attacker to execute arbitrary code with the privileges of the current user, potentially accessing all data the user can reach, including documents, credentials, and network resources. Integrity Impact is high as the attacker can install malware, modify system files, or establish persistent backdoor access. Availability Impact is high since the attacker can crash the browser or the entire system, and installed malware may consume system resources or render the machine unusable. The attack complexity is high (AC:H), meaning specific conditions must be met for exploitation, which provides some natural limitation. However, no privileges or user interaction beyond visiting a malicious webpage are required. The EPSS score of 0.8703 (99.4th percentile) indicates near-certain exploitation activity. As a zero-day that was actively exploited before patches were available, organizations that still run legacy Internet Explorer versions face severe risk. The KEV catalog listing with ransomware status "Unknown" emphasizes the urgency of ensuring no systems remain exposed to this vulnerability.
Exploit Maturity
CVE-2010-3962 has a fully mature exploit ecosystem. This vulnerability was exploited as a zero-day in the wild in November 2010 before Microsoft released a patch, making it one of the notable browser zero-days of that era. CISA has included it in the Known Exploited Vulnerabilities catalog with a remediation deadline of October 27, 2025, and ransomware association is listed as "Unknown." The EPSS score of 0.8703 (99.4th percentile) confirms an extremely high exploitation probability. Multiple public exploits were published on Exploit-DB (15418) and Exploit-DB (15421), providing working proof-of-concept code. The US-CERT also issued an advisory (VU#899748) documenting the active exploitation. The combination of public exploit availability, confirmed zero-day exploitation, and the widespread deployment of Internet Explorer at the time of disclosure made this one of the most significant browser vulnerabilities of 2010.
Remediation
- Apply Microsoft security update MS10-090. Install the cumulative security update for Internet Explorer that addresses CVE-2010-3962, available through the Microsoft Security Advisory 2458511. This patch fixes the use-after-free condition in the CSS rendering engine.
- Migrate away from Internet Explorer entirely. Internet Explorer 6, 7, and 8 are all end-of-life products that no longer receive security updates. Transition all users and web applications to a modern, supported browser such as Microsoft Edge, Google Chrome, or Mozilla Firefox to eliminate exposure to this and numerous other unpatched Internet Explorer vulnerabilities.
- Implement network-level protections. Deploy web content filtering and intrusion prevention systems (IPS) with signatures for CVE-2010-3962 exploit patterns to detect and block exploitation attempts targeting any remaining Internet Explorer instances on the network.
- Restrict ActiveX and scripting in Internet Explorer. If immediate migration is not possible, configure Internet Explorer security zones to disable Active Scripting and ActiveX controls in the Internet zone, or set the Internet security zone to "High" to reduce the attack surface.
- Deploy EMET or Windows Defender Exploit Guard. Use the Enhanced Mitigation Experience Toolkit (EMET) or its successor, Windows Defender Exploit Guard, to apply exploit mitigations such as DEP and ASLR enforcement to Internet Explorer, which can prevent successful exploitation even on unpatched systems.
Technical Details
The CVSS v3.1 vector for CVE-2010-3962 is CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H, yielding a score of 8.1 (High). Attack Vector (AV:N) is network, meaning the vulnerability can be exploited remotely over the internet, typically by luring a victim to a malicious or compromised website. Attack Complexity (AC:H) is high, indicating that successful exploitation requires winning a race condition or achieving specific heap layout conditions, which adds some difficulty to reliable exploitation. Privileges Required (PR:N) is none, as the attacker needs no authentication on the target system. User Interaction (UI:N) is none in the CVSS scoring, though in practice the user must navigate to a malicious page. Scope (S:U) is unchanged, meaning the impact is confined to the vulnerable component's security context. All three impact metrics — Confidentiality (C:H), Integrity (I:H), and Availability (A:H) — are rated high, reflecting complete compromise potential within the user's context.
The technical root cause involves Internet Explorer's handling of CSS token sequences in combination with the clip attribute. When the browser parses certain CSS constructs, it allocates a memory object to represent the style information. Under specific conditions involving the clip CSS property, the rendering engine frees this object but retains a pointer to it. When the engine subsequently processes related style operations, it dereferences the now-invalid pointer, accessing freed heap memory. An attacker can manipulate the heap through JavaScript to place controlled data at the freed memory location, effectively hijacking the object's virtual function table pointer. When the browser calls a method on the corrupted object, execution is redirected to attacker-controlled code, typically a ROP chain leading to shellcode execution.
Frequently Asked Questions
What is CVE-2010-3962 and how is it exploited?
CVE-2010-3962 is a use-after-free vulnerability in Microsoft Internet Explorer 6, 7, and 8 that occurs when the browser processes certain CSS token sequences combined with the clip attribute. An attacker exploits this by hosting a malicious webpage that triggers the use-after-free condition, allowing them to execute arbitrary code on the victim's machine when they visit the page.
Was CVE-2010-3962 exploited as a zero-day?
Yes, CVE-2010-3962 was actively exploited in the wild in November 2010 before Microsoft released a patch. It was used in targeted attacks, and Microsoft initially responded with Security Advisory 2458511 before issuing a full patch in the December 2010 cumulative update for Internet Explorer.
Are modern browsers affected by CVE-2010-3962?
No, CVE-2010-3962 only affects Microsoft Internet Explorer versions 6, 7, and 8, all of which are long end-of-life. Modern browsers such as Microsoft Edge, Google Chrome, and Mozilla Firefox are not affected. However, organizations that still maintain legacy systems running Internet Explorer remain at risk.
Why is CVE-2010-3962 still in the KEV catalog in 2025?
CISA includes older vulnerabilities in the KEV catalog when evidence suggests they continue to be exploited or when federal systems may still be exposed. Despite its age, CVE-2010-3962 remains relevant because some legacy environments still run Internet Explorer for compatibility with older web applications, and attackers continue to target such systems.
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