MSHTML Framework Zero-Day Opens Door to Network-Based Security Bypass

Microsoft has disclosed a new zero-day vulnerability in the MSHTML Framework that allows attackers to bypass security features, posing significant risks to organizations worldwide.

Tracked as CVE-2026-21513, this vulnerability was released on February 10, 2026, and has already been exploited in the wild.

The MSHTML Framework, a core Windows component used for rendering web content, contains a protection mechanism failure that enables unauthorized attackers to circumvent security controls remotely.

With a CVSS score of 8.8 out of 10, this vulnerability is classified as “Important” severity, making it a high-priority concern for security teams.

CVE ID	CVE-2026-21513 ​
Vulnerability Type	MSHTML Framework Security Feature Bypass Vulnerability ​
Release Date	February 10, 2026 ​
Assigning CNA	Microsoft ​
Severity Rating	Important ​
CVSS Score	8.8 / 7.7 (CVSS:3.1) ​

What makes this vulnerability particularly dangerous is its network-based attack vector.

Attackers don’t need any special privileges to exploit it, they simply need to trick a user into interacting with malicious content.

Once successful, attackers can gain high-level access to confidentiality, integrity, and availability of affected systems.

Technical Details

The vulnerability stems from a weakness classified as CWE-693, indicating a failure in the framework’s protection mechanisms.

The CVSS vector string (CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H) reveals several concerning characteristics:

• Attack complexity is low, making exploitation relatively straightforward
• No privileges are required to launch an attack
• User interaction is necessary, typically through social engineering
• All three security pillars confidentiality, integrity, and availability face high impact

Microsoft’s exploitability assessment confirms that this vulnerability has been both publicly disclosed and actively exploited.

The “Exploitation Detected” status indicates real-world attacks are underway, elevating the urgency for immediate action.

Despite exploitation occurring in the wild, the exploit code maturity remains “Unproven,” suggesting attacks may be limited or sophisticated.

However, this could change rapidly as more threat actors become aware of the vulnerability.

Organizations should prioritize patching affected systems immediately.

Microsoft has released an official fix, bringing the remediation level to “Official Fix” status. Security teams should:

• Apply Microsoft’s security updates without delay
• Monitor network traffic for suspicious MSHTML-related activity
• Educate users about potential phishing attempts exploiting this vulnerability
• Implement additional network security controls as temporary measures

Given the active exploitation and network-based attack vector, organizations cannot afford to delay remediation efforts for this critical security flaw.

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