Microsoft: MSHTML Framework 0-Day Vulnerability Let Attackers Security Feature over Network

Microsoft Patches Actively Exploited Zero-Day in MSHTML Framework (CVE-2026-21513)

Microsoft has released an emergency security update to address a critical zero-day vulnerability (CVE-2026-21513) in the MSHTML Framework, which was actively exploited in attacks before a fix was available. The flaw, classified as a security feature bypass, allows attackers to circumvent Windows protection mechanisms without requiring elevated privileges, exposing millions of systems to potential compromise.

The vulnerability affects the MSHTML (Trident) engine, a core component used by Windows and various applications to render HTML content. Due to its deep integration, the flaw impacts a broad range of systems, including Windows 10, Windows 11, and Windows Server editions from 2012 to 2025.

Exploitation relies on social engineering, where attackers trick users into opening malicious HTML files or shortcuts (.lnk) delivered via email, links, or downloads. Once opened, the crafted files bypass security prompts, enabling unauthorized actions such as code execution with a single click. The attack requires no privileges and is rated 8.8 (High) on the CVSS scale, indicating significant risk.

Microsoft confirmed that CVE-2026-21513 was both publicly disclosed and actively exploited as a zero-day prior to the patch. The U.S. Cybersecurity and Infrastructure Security Agency (CISA) added the vulnerability to its Known Exploited Vulnerabilities catalog, mandating federal agencies to apply fixes by March 3, 2026.

In enterprise environments, successful exploitation could lead to malware deployment, ransomware attacks, credential theft, data breaches, or full system compromise. The flaw’s ability to bypass security controls heightens the risk of phishing and malware campaigns.

Microsoft released the patch on February 10, 2026, as part of its Patch Tuesday cycle. Organizations are advised to prioritize deployment due to the vulnerability’s active exploitation in real-world attacks.

Source: https://cybersecuritynews.com/mshtml-framework-0-day-vulnerability/

Microsoft cybersecurity rating report: https://www.rankiteo.com/company/Microsoft

"id": "MIC1770817947",
"linkid": "Microsoft",
"type": "Vulnerability",
"date": "2/2026",
"severity": "85",
"impact": "4",
"explanation": "Attack with significant impact with customers data leaks"

{'affected_entities': [{'customers_affected': 'Millions of systems',
                        'industry': 'Software/IT',
                        'location': 'Global',
                        'name': 'Microsoft',
                        'size': 'Enterprise',
                        'type': 'Technology Company'}],
 'attack_vector': 'Social Engineering (Malicious HTML files/shortcuts)',
 'date_resolved': '2026-02-10',
 'description': 'Microsoft has released an emergency security update to '
                'address a critical zero-day vulnerability (CVE-2026-21513) in '
                'the MSHTML Framework, which was actively exploited in attacks '
                'before a fix was available. The flaw allows attackers to '
                'circumvent Windows protection mechanisms without requiring '
                'elevated privileges, exposing millions of systems to '
                'potential compromise.',
 'impact': {'operational_impact': 'Potential malware deployment, ransomware '
                                  'attacks, credential theft, data breaches, '
                                  'or full system compromise',
            'systems_affected': 'Windows 10, Windows 11, Windows Server '
                                '(2012-2025)'},
 'post_incident_analysis': {'corrective_actions': 'Patch deployment, user '
                                                  'awareness training on '
                                                  'social engineering risks',
                            'root_causes': 'Security feature bypass in MSHTML '
                                           'Framework (Trident engine)'},
 'recommendations': 'Organizations are advised to prioritize deployment of the '
                    'patch due to active exploitation in real-world attacks.',
 'references': [{'source': 'Microsoft Security Update'},
                {'source': 'CISA Known Exploited Vulnerabilities Catalog'}],
 'regulatory_compliance': {'regulatory_notifications': 'CISA Known Exploited '
                                                       'Vulnerabilities '
                                                       'catalog (mandatory '
                                                       'patch by March 3, '
                                                       '2026)'},
 'response': {'containment_measures': 'Emergency security update (patch)',
              'remediation_measures': 'Patch deployment (CVE-2026-21513)'},
 'title': 'Microsoft Patches Actively Exploited Zero-Day in MSHTML Framework '
          '(CVE-2026-21513)',
 'type': 'Zero-Day Vulnerability',
 'vulnerability_exploited': 'CVE-2026-21513'}