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

[Brownie2019]

Content source

https://gbhackers.com/mshtml-framework-zero-day/

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.

Full Story:

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.

gbhackers.com

 

[Halp2001]

A zero‑day in MSHTML is like discovering that the fortress had a secret passage no one had noticed: no matter how many sentinels you place, if the stone itself gives way, the enemy is already inside. The lesson is clear: defense in layers is not a luxury, it’s the only way to keep a flaw in the core from turning into a total collapse.

 

[Divergent]

Technical Analysis & Remediation

CVE Profile

ID
CVE-2026-21513

CVSS v3.1 Score
8.8 (High)

Vector String CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H

CWE Classification
CWE-693 (Protection Mechanism Failure)

Attack Vector & Behavior

Delivery
The attack is Network-based (AV:N) but requires User Interaction (UI:R). This suggests delivery via social engineering, where a user is tricked into opening a malicious document or visiting a crafted webpage.

Mechanism
The vulnerability exploits a failure in the MSHTML protection mechanism. Successful exploitation grants the attacker the ability to bypass security controls, impacting Confidentiality, Integrity, and Availability.

Privileges
No elevated privileges are required to initiate the attack (PR:N).

Exploit Status
Microsoft reports "Exploitation Detected," though the public exploit code maturity is currently listed as "Unproven," suggesting targeted usage rather than automated wormable exploits at this stage.

Remediation - THE ENTERPRISE TRACK
Actions mapped to NIST CSF 2.0 Functions.

GOVERN (GV) & IDENTIFY (ID)

Command
Audit the asset inventory for systems running the unpatched February 2026 stack.

Command
Prioritize endpoints with frequent exposure to external email and web content (e.g., HR, Finance, Executive Support).

PROTECT (PR)

Command
PATCH IMMEDIATELY. Deploy the "Official Fix" released on Feb 10, 2026.

Command
Review "IE Mode" usage in Microsoft Edge policies. Restrict legacy MSHTML rendering to trusted sites only if immediate patching is impossible.

DETECT (DE)

Command
Monitor network traffic for suspicious MSHTML-related anomalies or unexpected outbound connections from legacy processes (e.g., iexplore.exe, mshta.exe, or Office apps).

Command
Alert on unexpected child processes spawned by Office applications, which may indicate successful exploitation of the rendering engine.

RESPOND (RS)

Command
If exploitation is suspected, isolate the host immediately.

Command
Collect browser history and temporary internet files for forensic analysis to identify the delivery vector (URL or file).

Remediation - THE HOME USER TRACK

Priority 1: Update Windows

Command
Go to Settings > Windows Update and click "Check for updates" immediately. Ensure the February 2026 Cumulative Update is installed.

Priority 2: Hyper-Vigilance

Command
Be extremely cautious with links in emails or unsolicited attachments. This exploit relies on you clicking the malicious content.

Priority 3: Browser Safety

Command
Use a modern browser (Chrome, Firefox, or Edge in standard mode) that does not rely on the legacy MSHTML engine by default for general browsing.

Source

GBHackers Security

Microsoft Security Response Center

MITRE CVE Record