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Microsoft Defender Zero-Day Vulnerabilities RedSun and UnDefend Actively Exploited on Windows 10, 11, and Server (April 2026 CVE Analysis)
Winsage
May 21, 2026

Microsoft Defender Zero-Day Vulnerabilities RedSun and UnDefend Actively Exploited on Windows 10, 11, and Server (April 2026 CVE Analysis)

In April 2026, two zero-day vulnerabilities, RedSun and UnDefend, were discovered in Microsoft Defender, affecting Windows 10, Windows 11, and Windows Server platforms. These vulnerabilities allow attackers to escalate privileges to SYSTEM and bypass Defender’s protections. RedSun exploits a flaw in Defender's remediation process, enabling low-privileged users to overwrite critical system files. UnDefend allows attackers to disrupt Defender’s updates, keeping it outdated and ineffective. Both vulnerabilities are actively being exploited, with attackers leveraging them to gain persistent access and deploy ransomware. The primary targets are organizations using Windows systems with Defender enabled, particularly in sectors like finance, healthcare, and government. Mitigation strategies include applying updates for related vulnerabilities, monitoring for suspicious activities, and implementing additional security measures.
MSHTA abuse helps malware hide in Windows processes
Winsage
May 20, 2026

MSHTA abuse helps malware hide in Windows processes

Bitdefender's research highlights the use of Microsoft's MSHTA utility in malware attacks, noting its default activation in Windows systems. Cybercriminals exploit MSHTA to execute malicious scripts under the guise of legitimate processes, linking it to various malware families like LummaStealer and PurpleFox. The study reports a rise in MSHTA-related detections, indicating a shift towards "living-off-the-land" tactics that utilize legitimate tools to evade security alerts. Social engineering is identified as a common entry point for attacks, employing deceptive methods such as fake software downloads and phishing links. MSHTA can retrieve and execute additional payloads through multi-stage chains, complicating detection efforts. The attacks target sensitive information, including credentials and financial data, and the continued presence of MSHTA poses risks as it allows threat actors to conceal malicious actions. To mitigate these threats, organizations are advised to restrict or disable legacy scripting tools and exercise caution with untrusted downloads. The report emphasizes the challenge of detecting unusual behaviors associated with legitimate utilities in the context of cyber threats.
Trapdoor Android Ad Fraud Scheme Hit 659 Million Daily Bid Requests Using 455 Apps
AppWizard
May 20, 2026

Trapdoor Android Ad Fraud Scheme Hit 659 Million Daily Bid Requests Using 455 Apps

Cybersecurity researchers have identified an ad fraud and malvertising operation called Trapdoor, targeting Android users with 455 malicious applications and 183 command-and-control domains. Users often download these disguised apps, which initiate malvertising campaigns and lead to further downloads of malicious applications. At its peak, Trapdoor generated 659 million bid requests daily, with over 24 million downloads of the associated apps, primarily from the United States. The operation exploits install attribution tools to activate malicious activities only for users acquired through fraudulent ad campaigns, while suppressing such behavior for organic downloads. Trapdoor employs advanced evasion techniques, including obfuscation and impersonation of legitimate software, to avoid detection. Google has removed the identified malicious apps from the Play Store in response to the threat.
ScarCruft hackers push BirdCall Android malware via game platform
BetaBeacon
May 5, 2026

ScarCruft hackers push BirdCall Android malware via game platform

APT37, also known as ScarCruft and Ricochet Chollima, has developed an Android version of the backdoor BirdCall, which serves as spyware in addition to a backdoor. The malware was delivered through a Chinese website that hosts games for Android, iOS, and Windows, targeting only Android and Windows systems. The Android variant of BirdCall has capabilities such as extracting IP geolocation information, collecting contact lists, call logs, SMS data, device information, taking screenshots, recording audio, and exfiltrating files. Users are advised to download software only from official marketplaces and trusted publisher sites to protect against malware infections.
North Koreans Spy on Defectors Via Android Game Apps
AppWizard
May 5, 2026

North Koreans Spy on Defectors Via Android Game Apps

A North Korean hacking group has targeted a digital gaming platform popular among the Korean ethnic enclave in China, using a sophisticated strategy to infiltrate Android applications. Researchers from Eset discovered that an app on the platform contained a backdoor known as BirdCall, linked to North Korea. The official website for the gaming platform hosted the same suspicious APK file. A second Android file associated with another game on the same site was also found to contain the BirdCall backdoor. This supply-chain attack was attributed to the threat actor ScarCruft (APT37), active in Asia and extending into Europe and the Middle East since late 2024. The hackers likely compromised the web server to recompile original APKs with the backdoor, which can collect sensitive information such as contacts, SMS messages, call logs, documents, media files, and private keys, and can take screenshots and record audio. The malware disguises its command and control traffic among regular internet traffic, primarily using Zoho WorkDrive for operations.
Defender yanks root certs as Windows updates blocks backups
Winsage
May 5, 2026

Defender yanks root certs as Windows updates blocks backups

Microsoft's Defender anti-malware tool update version 1.449.425.0 removed two DigiCert root digital certificates, leading to false positives that flagged them as severe malware (Trojan:Win32/Cerdigent.A!dha). This incident was later identified as a false positive, and updating to version 1.449.430.0 or later reinstates the certificates. The issue may be linked to a DigiCert employee encountering disguised malware. Additionally, Windows updates from April 14 caused third-party backup applications to malfunction due to the addition of vulnerable psmounterex.sys kernel driver versions to a blocklist. Users experienced difficulties with mounting backup image files, and Microsoft referenced a vulnerability rated 9.3 out of 10 in the driver. Other affected software includes Acronis Cyber Protect Cloud and UrBackup server. Microsoft has not explained the delay in adding the vulnerable driver to the blocklist, and other recent update-related issues have also been reported.
Microsoft Defender wrongly flags DigiCert certs as Trojan:Win32/Cerdigent.A!dha
Tech Optimizer
May 4, 2026

Microsoft Defender wrongly flags DigiCert certs as Trojan:Win32/Cerdigent.A!dha

Microsoft Defender mistakenly flagged legitimate DigiCert root certificates as Trojan:Win32/Cerdigent.A!dha, leading to their removal from Windows systems globally. This issue arose after a Defender signature update on April 30th, with affected certificates including 0563B8630D62D75ABBC8AB1E4BDFB5A899B24D43 and DDFB16CD4931C973A2037D3FC83A4D7D775D05E4. The certificates were removed from the AuthRoot store under the Registry key HKLMSOFTWAREMicrosoftSystemCertificatesAuthRootCertificates. Microsoft has addressed the issue in Security Intelligence update version 1.449.430.0, which also restored the removed certificates. The false positives were linked to detections related to a recent DigiCert breach, where threat actors obtained valid code-signing certificates used for signing malware. DigiCert revoked 60 code-signing certificates, including those linked to the "Zhong Stealer" malware campaign. The malware utilized certificates issued to companies like Lenovo and Kingston, but the certificates flagged by Microsoft Defender are root certificates and do not correspond to the revoked code-signing certificates.
Mirax RAT Targets Android Devices Through Meta Apps
AppWizard
April 14, 2026

Mirax RAT Targets Android Devices Through Meta Apps

Mirax is a remote access Trojan (RAT) targeting Android devices in Spanish-speaking countries, identified by Outpost24's KrakenLabs in early March. It propagates fraudulent advertisements on Meta-owned applications, allowing cybercriminals to gain initial access. Mirax can interact with compromised devices in real time, converting them into residential proxy nodes through ads on platforms like Facebook and Instagram. It uses SOCKS5 protocol and Yamux multiplexing to establish proxy channels and uncover victims' IP addresses. The malware captures keystrokes, steals sensitive data, executes commands, and monitors user activity. It employs overlay pages to steal credentials and orchestrates distribution through Meta ads and GitHub for malicious APK files. Users are tricked into enabling installations from "unknown sources," and the malware disguises itself behind video playback features. Additionally, a threat actor has been offering Mirax as a malware-as-a-service (MaaS) on illicit forums, with subscription prices starting at ,500 for three months. This service is described as highly controlled and exclusive, primarily targeting Russian-speaking actors in underground communities.
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