New Windows Flaw Lets Attackers Bypass Mark of the Web
Microsoft has released security updates to address a Windows Remote Assistance vulnerability that could allow attackers to bypass Mark of the Web (MOTW) protections.
This weakens a core Windows defense that helps flag and restrict risky files downloaded from untrusted sources. Exploitation of the vulnerability could allow an attacker to “… evade Mark of the Web (MOTW) defenses,” Microsoft said in its advisory.
The company has released a patch for the vulnerability on Jan. 13.
How the MOTW bypass works
This vulnerability (CVE-2026-20824) is classified as a protection mechanism failure and has a CVSS score of 5.5, indicating it is not a remote wormable issue but still poses meaningful risk in real-world attack chains.
Exploitation requires local execution and user interaction, meaning attackers can’t trigger it automatically at scale without first getting a target to open a file or launch a malicious payload.
In practice, the most common path for exploitation is social engineering, where a user is tricked into opening a specially crafted file delivered through phishing emails, collaboration tools, or a download from a compromised or attacker-controlled website.
The weakness stems from how Windows Remote Assistance validates and processes downloaded content, allowing an attacker to bypass Mark of the Web (MOTW) enforcement.
MOTW is one of Windows’ important early warning signals, marking files that originate from the internet so the operating system and security controls can apply extra safeguards. Those safeguards often include security prompts, restricted execution behavior, and additional inspection by endpoint security tools.
When MOTW protections are bypassed, attackers gain a quieter path to execute file-based payloads with less friction. That can reduce the effectiveness of controls that rely on MOTW metadata to block or flag suspicious activity — particularly in environments where phishing remains the primary initial access vector.
Even if this vulnerability is not currently being exploited in the wild, the ability to weaken MOTW-driven defenses makes it valuable to adversaries looking to increase success rates and evade early detection.
How to mitigate the MOTW bypass risk
Although this Windows Remote Assistance issue isn’t easily exploited at scale, it can weaken Mark of the Web protections that help flag and restrict risky downloaded files.
Organizations should combine timely patching with stronger file execution controls and focused monitoring:
- Apply the latest patches across affected Windows systems, prioritizing user-facing endpoints.
- Harden email and web controls by enforcing SPF/DKIM/DMARC, blocking high-risk attachment types, and reducing exposure to untrusted downloads and phishing lures.
- Enforce endpoint protections that reduce file-based execution risk, including SmartScreen, Attack Surface Reduction rules, and Protected View policies.
- Implement application control (WDAC/AppLocker) to prevent unapproved scripts and binaries from running, especially from user-writable locations like Downloads and AppData.
- Restrict Windows Remote Assistance where possible by disabling it when not needed and limiting who can initiate or accept sessions via policy.
- Improve detection and readiness by monitoring suspicious file execution patterns and strengthening alerting for abnormal process behavior.
- Test incident response plans for file-based attacks to ensure rapid response if MOTW bypass activity is suspected.
These steps help organizations reduce the attack surface and limit blast radius in the event of exploitation.
Why MOTW bypass still matters
Ultimately, this Windows Remote Assistance vulnerability reinforces how much modern defense depends on layered controls working together — especially protections like MOTW that help reduce risk from everyday downloads and phishing-driven payloads.
While exploitation requires user interaction, bypassing MOTW can remove a key safety signal, increasing the likelihood that file-based attacks succeed with fewer warnings and fewer detection opportunities.
Organizations should prioritize patching, tighten controls over email and endpoint execution, and validate monitoring coverage for suspicious file behavior to reduce exposure.
Editor’s note: This article first appeared on our sister publication, eSecurityPlanet.com.
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