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More than one information-stealer incident has involved a Windows SmartScreen bypass vulnerability, so the phrase does not identify one attack or one malware family. A 2023 example involved Phemedrone Stealer and CVE-2023-36025; separate 2024 reporting described infostealer delivery using CVE-2024-21412. SmartScreen still works in Microsoft Edge and Windows Shell, but it is one layer of protection—not a guarantee that a file or link is safe.
What “information stealer exploits a SmartScreen bypass” means
An information stealer is malware designed to collect sensitive information from a device or its applications. In the reported cases discussed here, attackers used vulnerabilities associated with bypassing a SmartScreen warning as part of a delivery chain. That does not mean SmartScreen itself is malware, or that every infostealer uses the same vulnerability or technique.
The distinction matters: Phemedrone Stealer was reported in connection with CVE-2023-36025, while separate 2024 reporting described an infostealer chain associated with CVE-2024-21412. These are different examples, not stages of one campaign. The sources cited here do not establish a total number of victims or infections.
How SmartScreen and Mark of the Web fit together
SmartScreen checks reputation
Microsoft Defender SmartScreen checks websites against dynamic lists of reported phishing and malware sites and evaluates downloaded apps and installers using reputation information. A file that lacks an established reputation may prompt a warning. That warning is a signal to stop and verify—not proof on its own that a file is malicious or safe.
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Mark of the Web records file origin
Windows Attachment Manager uses security information called Mark of the Web (MotW) to help decide whether downloaded or otherwise untrusted files should show a warning or receive other protections. Microsoft advises checking where a file came from, scanning it, confirming its type matches the expected download, and treating unexpected attachments cautiously. SmartScreen does not protect against malicious files on internal locations or network shares, according to Microsoft.
Does SmartScreen still work in Windows 11?
Yes. Microsoft’s November 2025 support article says SmartScreen remains active in Microsoft Edge and Windows Shell. The documented deprecation applies to Internet Explorer and IE Mode on Windows 11; downloaded files in those scenarios continue to receive MotW tags for evaluation by SmartScreen in Windows Shell when opened. This is not a general removal of SmartScreen from Windows 11.
Documented SmartScreen-bypass-related stealer examples
| Vulnerability | Reported example | What the source says |
|---|---|---|
| CVE-2023-36025 | Phemedrone Stealer | A Peru National Digital Security Center alert dated January 15, 2024 described delivery through exploitation of this vulnerability. It said the stealer could collect sensitive data from browsers, cryptocurrency wallets, messaging apps, and other system information. |
| CVE-2024-21412 | A separately reported infostealer delivery chain | A CERT-aDvens July 2024 threat-intelligence report, citing Cyble, described a crafted URL file leading to a malicious LNK hosted on WebDAV, followed by use of legitimate Windows utilities and later payload stages. This is a reported campaign chain, not a universal exploit recipe. |
In a February 14, 2024 advisory, CERT-EU reported that Microsoft had observed in-the-wild exploitation of CVE-2024-21351 and CVE-2024-21412. CERT-EU listed CVSS severity scores of 7.6 for CVE-2024-21351 and 8.1 for CVE-2024-21412. Those scores describe vulnerability severity; they are not infection counts. CERT-EU recommended promptly applying the February 2024 security updates for affected products.
Why a SmartScreen bypass is only part of the threat
A bypass can weaken one warning or protection point, but stealer campaigns also depend on how a file or link reaches a person and what happens after it is opened. Microsoft’s May 21, 2025 Lumma Stealer research describes Lumma as malware-as-a-service that can steal data from browsers and applications, including cryptocurrency wallets, and install other malware. Microsoft identifies phishing, malvertising, abuse of trusted platforms, and traffic-distribution systems among evolving delivery methods.
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This broader context is why avoiding a single suspicious file is not a complete security plan. A warning mechanism can reduce risk, endpoint controls can help detect or block malicious activity, and stronger sign-in methods can limit the damage if credentials are exposed. None of these measures guarantees that an infection cannot happen.
How to reduce the risk
Keep Windows and browsers supported and updated
Install supported Windows and browser updates, including applicable security updates. For affected products in February 2024, CERT-EU specifically advised applying that month’s updates promptly; for current protection, use the updates offered for the Windows version and browser you run.
Handle downloads and links cautiously
- Do not open unexpected email attachments or follow unexpected links.
- Verify a file’s source before opening it, and check that its file type matches what you intended to download.
- Scan files when appropriate. Do not treat a missing SmartScreen warning as proof that a file is safe, particularly for files from internal locations or network shares.
Use endpoint protections
Microsoft’s Lumma recommendations include enabling endpoint protections and attack-surface-reduction rules, and using Microsoft Edge with SmartScreen. On a managed work device, follow the organization’s security policy; administrators may control which endpoint protections and rules are enabled.
Strengthen account sign-in
Microsoft Threat Intelligence, Microsoft Digital Crimes Unit, and Microsoft Defender Experts recommend: “Require multifactor authentication (MFA).” They recommend phishing-resistant methods such as FIDO tokens or Microsoft Authenticator with passkey. A FIDO2 security key can strengthen sign-in security, but it does not patch a Windows vulnerability, prevent every stealer infection, or remove malware from an infected device.
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What to do if you opened a suspicious file
- Stop interacting with it. Do not enter passwords or payment information into anything opened from the suspicious file or link.
- Use your endpoint protection. Run the security checks available on the device and follow any remediation instructions. On a work device, contact your organization’s IT or security team.
- Protect potentially exposed accounts from a trusted device. Change affected passwords and enable MFA, prioritizing phishing-resistant sign-in where available.
- Keep the device updated. Install supported Windows and browser updates, and seek help from your IT team or a qualified support provider if you suspect malware remains present.
These steps address likely exposure and account risk; changing a password alone should not be treated as malware removal.
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