CyberHappenings logo
☰
Home Browse About

Track cybersecurity events as they unfold. Sourced timelines. Filter, sort, and browse. Fast, privacy‑respecting. No invasive ads, no tracking.

Active Exploitation of Critical Microsoft WSUS Flaw

First reported
Last updated
3 unique sources, 4 articles

Summary

Hide ▲

A critical vulnerability in Microsoft Windows Server Update Service (WSUS), CVE-2025-59287, is being actively exploited in the wild. This flaw, with a CVSS score of 9.8, allows attackers to drop malicious payloads and execute arbitrary commands on infected hosts. The vulnerability affects WSUS versions 3.32.x and was discovered by Eye Security and Huntress. The Cybersecurity and Infrastructure Security Agency (CISA) has ordered U.S. government agencies to patch the flaw, which was added to the Known Exploited Vulnerabilities catalog. Organizations using WSUS are advised to apply the out-of-band security updates provided by Microsoft to mitigate the risk of exploitation. The flaw was originally patched by Microsoft as part of its Patch Tuesday updates, but attackers have since weaponized it to deploy .NET executables and Base64-encoded PowerShell scripts. Shadowserver is tracking over 2,800 WSUS instances with default ports exposed online. The vulnerability is a deserialization of untrusted data flaw that allows unauthenticated attackers to achieve remote code execution with system privileges by sending malicious encrypted cookies to the GetCookie() endpoint. A compromised WSUS server could potentially be used to distribute malicious updates to the entire network of client computers, making it particularly dangerous for large enterprises. Huntress advised isolating network access to WSUS and blocking inbound traffic to TCP ports 8530 and 8531 as remediation steps. The out-of-band (OOB) security update KB5070881 for CVE-2025-59287 broke hotpatching on some Windows Server 2025 devices. Microsoft has released a new update, KB5070893, to address the issue without disrupting hotpatching. Administrators are advised to install this update to maintain hotpatching functionality.

Timeline

  1. 03.11.2025 17:22 1 articles · 7d ago

    Microsoft releases fix for hotpatching disruption

    The out-of-band (OOB) security update KB5070881 for CVE-2025-59287 broke hotpatching on some Windows Server 2025 devices. Microsoft has released a new update, KB5070893, to address the issue without disrupting hotpatching. Administrators are advised to install the KB5070893 update to maintain hotpatching functionality. Microsoft has also turned off the display of synchronization error details within its WSUS error reporting to address the vulnerability.

    Show sources
    Open in new tab
  2. 27.10.2025 14:51 4 articles · 14d ago

    Active Exploitation of Critical WSUS Flaw Disclosed

    The Cybersecurity and Infrastructure Security Agency (CISA) ordered U.S. government agencies to patch the WSUS vulnerability, CVE-2025-59287. This flaw is a potentially wormable remote code execution (RCE) vulnerability affecting Windows servers with the WSUS Server role. HawkTrace Security released proof-of-concept exploit code, leading Microsoft to issue out-of-band security updates. IT administrators are advised to disable the WSUS Server role on vulnerable systems if immediate patching is not possible. Shadowserver is tracking over 2,800 WSUS instances with default ports exposed online. The vulnerability is a deserialization of untrusted data flaw that allows unauthenticated attackers to achieve remote code execution with system privileges by sending malicious encrypted cookies to the GetCookie() endpoint. A compromised WSUS server could potentially be used to distribute malicious updates to the entire network of client computers. Huntress advised isolating network access to WSUS and blocking inbound traffic to TCP ports 8530 and 8531 as remediation steps. The Netherlands National Cyber Security Centre (NCSC-NL) confirmed the active exploitation of the flaw. The out-of-band (OOB) security update KB5070881 for CVE-2025-59287 broke hotpatching on some Windows Server 2025 devices. Microsoft has released a new update, KB5070893, to address the issue without disrupting hotpatching. Microsoft has also turned off the display of synchronization error details within its WSUS error reporting to address the vulnerability.

    Show sources
    Open in new tab

Information Snippets

Similar Happenings

Critical WSUS RCE Vulnerability Exploited in the Wild

A critical remote code execution (RCE) vulnerability (CVE-2025-59287) in Windows Server Update Service (WSUS) is being actively exploited in the wild. The flaw allows attackers to run malicious code with SYSTEM privileges on Windows servers with the WSUS Server role enabled. Microsoft has released out-of-band patches for all affected Windows Server versions. Cybersecurity firms have observed exploitation attempts and the presence of publicly available proof-of-concept exploit code. The vulnerability is considered potentially wormable between WSUS servers and poses a significant risk to organizations. The flaw concerns a case of deserialization of untrusted data in WSUS. The vulnerability was discovered and reported by security researchers MEOW, f7d8c52bec79e42795cf15888b85cbad, and Markus Wulftange with CODE WHITE GmbH. CISA and NSA, along with international partners, have issued guidance to secure Microsoft Exchange Server instances, including recommendations to restrict administrative access, implement multi-factor authentication, and enforce strict transport security configurations. The agencies advise decommissioning end-of-life on-premises or hybrid Exchange servers after transitioning to Microsoft 365. Sophos reported threat actors exploiting the vulnerability to harvest sensitive data from U.S. organizations across various industries, with at least 50 victims identified. The exploitation activity was first detected on October 24, 2025, a day after Microsoft issued the update. Attackers use Base64-encoded PowerShell commands to exfiltrate data to a webhook[.]site endpoint. Michael Haag of Splunk noted an alternate attack chain involving the Microsoft Management Console binary (mmc.exe) to trigger cmd.exe execution.

Open in new tab

HTTP Request Smuggling Vulnerability in ASP.NET Core Kestrel Web Server

Microsoft patched a high-severity HTTP request smuggling vulnerability (CVE-2025-55315) in the Kestrel web server for ASP.NET Core. The flaw could allow authenticated attackers to hijack user credentials or bypass security controls. The vulnerability affects multiple versions of ASP.NET Core and has been addressed with security updates. Microsoft advises developers and users to update their applications to mitigate potential attacks.

Open in new tab

Microsoft October 2025 Patch Tuesday fixes 6 zero-days, 183 flaws

Microsoft's October 2025 Patch Tuesday marks the end of free security updates for Windows 10, with the release of the final cumulative update KB5066791. This update addresses 183 vulnerabilities, including six zero-day flaws, and is mandatory for all Windows 10 users. Extended Security Updates (ESU) are available for purchase for up to three years for enterprise users and one year for consumers. The patches cover a range of vulnerabilities, including critical remote code execution and elevation of privilege issues. The zero-day vulnerabilities affect various components, such as Windows SMB Server, Microsoft SQL Server, Windows Agere Modem Driver, Windows Remote Access Connection Manager, AMD EPYC processors, and TCG TPM 2.0. Some of these flaws have been publicly disclosed or actively exploited. The update also includes fixes for vulnerabilities in third-party components, such as IGEL OS and AMD EPYC processors. Additionally, Microsoft Office users should be aware of CVE-2025-59227 and CVE-2025-59234, which exploit the Preview Pane. The update is the largest on record for Microsoft, with 183 CVEs, pushing the number of unique vulnerabilities released so far this year to more than 1,021. The update includes fixes for a wide range of vulnerabilities, including remote code execution (RCE), elevation of privilege, data theft, denial of service (DoS), and security feature bypass issues. The update also marks the end of life for Windows 10, meaning Microsoft will no longer issue regular patches for vulnerabilities in the operating system as part of its regular Patch Tuesday updates. Exchange Server 2016, Exchange Server 2019, Skype for Business 2016, Windows 11 IoT Enterprise Version 22H2, and Outlook 2016 are also reaching end-of-life. Windows 10 users can opt for Extended Security Updates (ESU) for one year at a cost of $30, or install Linux as an alternative. Linux Mint is recommended for Windows 10 users transitioning to Linux, with compatibility for most computers from the last decade. The October 2025 Windows security updates cause smart card authentication and certificate issues across all Windows 10, Windows 11, and Windows Server releases. The issue is due to a security fix designed to address a security feature bypass vulnerability (CVE-2024-30098) in the Windows Cryptographic Services. Affected users may experience various symptoms, including the inability to sign documents, failures in applications using certificate-based authentication, and smart cards not being recognized as CSP providers in 32-bit apps. The issue can be detected by the presence of Event ID 624 in the System event logs for the Smart Card Service prior to installing the October 2025 Windows security update. The fix is enabled by setting the DisableCapiOverrideForRSA registry key value to 1 to isolate cryptographic operations from the Smart Card implementation. Users experiencing authentication problems can manually resolve the issue by disabling the DisableCapiOverrideForRSA registry key. The DisableCapiOverrideForRSA registry key will be removed in April 2026, and users are advised to work with their application vendors to resolve the underlying problem. Microsoft also fixed another known issue breaking IIS websites and HTTP/2 localhost (127.0.0.1) connections after installing recent Windows security updates. Microsoft has released out-of-band (OOB) security updates for a critical-severity Windows Server Update Service (WSUS) vulnerability (CVE-2025-59287) with publicly available proof-of-concept exploit code. The vulnerability can be exploited remotely in low-complexity attacks that do not require user interaction, allowing threat actors without privileges to target vulnerable systems and run malicious code with SYSTEM privileges. Microsoft has released security updates for all impacted Windows Server versions, including Windows Server 2025, Windows Server 2022, Windows Server 2019, Windows Server 2016, Windows Server 2012 R2, and Windows Server 2012. Workarounds for admins who can't immediately install these emergency patches include disabling the WSUS Server Role or blocking all inbound traffic to Ports 8530 and 8531 on the host firewall. The OOB update supersedes all previous updates for affected versions, and users are advised to install it as soon as possible.

Open in new tab

Microsoft Releases October 2025 Patch Tuesday Updates for Windows 11

Microsoft has released Windows 11 cumulative updates KB5066835 and KB5066793 for versions 25H2/24H2 and 23H2. These updates address security vulnerabilities and various issues. The updates are mandatory as they include the October 2025 Patch Tuesday security patches. The updates fix several issues across different components, including browsers, gaming, PowerShell, Windows Hello, and more. Additionally, new features and improvements have been introduced, such as enhanced AI actions in File Explorer and improved accessibility features in Narrator. The updates also mark the second-to-last update for Windows 11 23H2, as its support ends in November 2025.

Open in new tab

Critical Deserialization RCE Vulnerability in SolarWinds Web Help Desk

SolarWinds has released a third patch to address a critical deserialization vulnerability (CVE-2025-26399) in Web Help Desk 12.8.7 and earlier versions. This flaw allows unauthenticated remote code execution (RCE) on affected systems. The vulnerability was discovered by an anonymous researcher and reported through Trend Micro's Zero Day Initiative (ZDI). The flaw is a patch bypass for CVE-2024-28988, which itself was a bypass for CVE-2024-28986. The original vulnerability was exploited in the wild and added to the Known Exploited Vulnerabilities (KEV) catalog by CISA. SolarWinds advises users to update to version 12.8.7 HF1 to mitigate the risk. SolarWinds Web Help Desk is a help desk and ticketing suite used by medium-to-large organizations for IT support request tracking, workflow automation, asset management, and compliance assurance. The vulnerability affects the AjaxProxy component, and the hotfix requires replacing specific JAR files.

Open in new tab