{"id":1003,"date":"2026-05-21T12:44:46","date_gmt":"2026-05-21T12:44:46","guid":{"rendered":"https:\/\/thedigitalfortress.us\/?p=1003"},"modified":"2026-05-21T12:44:46","modified_gmt":"2026-05-21T12:44:46","slug":"microsoft-warns-of-two-actively-exploited-defender-vulnerabilities","status":"publish","type":"post","link":"https:\/\/thedigitalfortress.us\/?p=1003","title":{"rendered":"Microsoft Warns of Two Actively Exploited Defender Vulnerabilities"},"content":{"rendered":"<div>\n<p><span class=\"p-author\"><i class=\"icon-font icon-user\">\ue804<\/i><span class=\"author\">Ravie Lakshmanan<\/span><i class=\"icon-font icon-calendar\">\ue802<\/i><span class=\"author\">May 21, 2026<\/span><\/span><span class=\"p-tags\">Endpoint Security \/ Vulnerability<\/span><\/p>\n<\/div>\n<div id=\"articlebody\">\n<div class=\"separator\" style=\"clear: both;\"><a href=\"https:\/\/blogger.googleusercontent.com\/img\/b\/R29vZ2xl\/AVvXsEiNxp-fCwFOYcXoyRTmhjpwfvFCjfE36YoU8z-7es2XrOajnfSfpttiB9KMfwqCNbwzHQ85kILhlUwo4DeQFWXFq29J8p_oVAIe-gKCCegmTid4YW_22sK6CQO_TwELXa7Z-RZmvDvHx7N3Vg7y-xm78iSGjzCg2AU3FnHo1Hp7v80JJkBruCc05JVvVwnx\/s1700-e365\/windows-defender.jpg\" style=\"clear: left; display: block; float: left;  text-align: center;\"><\/a><\/div>\n<p>Microsoft has disclosed that a privilege escalation and a denial-of-service flaw in Defender has come under active exploitation in the wild.<\/p>\n<p>The former, tracked as <b><a href=\"https:\/\/msrc.microsoft.com\/update-guide\/vulnerability\/CVE-2026-41091\" target=\"_blank\">CVE-2026-41091<\/a><\/b>, is rated 7.8 on the CVSS scoring system. Successful exploitation of the flaw could allow an attacker to gain SYSTEM privileges.<\/p>\n<p>\u00abImproper link resolution before file access (&#8216;link following&#8217;) in Microsoft Defender allows an authorized attacker to elevate privileges locally,\u00bb Microsoft said in an advisory.<\/p>\n<p>The second vulnerability under exploitation is <b><a href=\"https:\/\/msrc.microsoft.com\/update-guide\/vulnerability\/CVE-2026-45498\" target=\"_blank\">CVE-2026-45498<\/a><\/b> (CVSS score: 4.0), a denial-of-service bug impacting Defender. The two vulnerabilities have been addressed in Microsoft Defender Antimalware Platform versions 1.1.26040.8 and 4.18.26040.7, respectively.<\/p>\n<div class=\"dog_two clear\">\n<div class=\"cf\"><a href=\"https:\/\/thehackernews.uk\/threatlabz-vpn-risk-2026-d\" rel=\"nofollow noopener sponsored\" target=\"_blank\"><img loading=\"lazy\" decoding=\"async\" class=\"lazyload\" alt=\"Cybersecurity\" src=\"https:\/\/blogger.googleusercontent.com\/img\/b\/R29vZ2xl\/AVvXsEhnNON5UeWywT7OcPNw7V4L7QNWnCnm7Xl_99Y9ek8dL-gRwx-bWxQM1TKqt8deqqrdpUyKMuuijAWyyPQVB0s0qf8ntQ6ldFAJLru-QUWhddKTopc7SeNbBBnd-TsfFyRPP-AAyDuclLlL6XHK4_LXqDC_7eyaz9pzToYr7U543MhrJ7qcK-89sVWHTQUZ\/s728-e100\/zz-2-d.jpg\" width=\"729\" height=\"91\"\/><\/a><\/div>\n<\/div>\n<p>The tech giant noted that systems that have disabled Microsoft Defender are not susceptible to the vulnerability, adding that no action is required to install the update since it automatically updates malware definitions and the Microsoft Malware Protection Engine for optimal protection.<\/p>\n<p>Microsoft credited five different parties with discovering and reporting the flaw, including Sibusiso, Diffract, Andrew C. Dorman  (aka ACD421), Damir Moldovanov, and an anonymous researcher.<\/p>\n<p>To ensure the latest version of the Microsoft Malware Protection Platform and definition updates are being actively downloaded and installed, users are recommended to follow the steps below:<\/p>\n<ul>\n<li>Open the <b>Windows Security<\/b> program.<\/li>\n<li>In the navigation pane, select <b>Virus &amp; threat protection<\/b>.<\/li>\n<li>Then click on <b>Protection Updates<\/b> in the Virus &amp; threat protection section updates.<\/li>\n<li>Select <b>Check for updates<\/b>.<\/li>\n<li>In the navigation pane, select <b>Settings<\/b>, and then select <b>About<\/b>.<\/li>\n<li>Examine the <b>Antimalware ClientVersion<\/b> number.<\/li>\n<\/ul>\n<p>There are currently no details on how the vulnerabilities are being exploited in the wild. The U.S. Cybersecurity and Infrastructure Security Agency (CISA) has <a href=\"https:\/\/www.cisa.gov\/news-events\/alerts\/2026\/05\/20\/cisa-adds-seven-known-exploited-vulnerabilities-catalog\" target=\"_blank\">added<\/a> both of them to its Known Exploited Vulnerabilities (<a href=\"https:\/\/www.cisa.gov\/known-exploited-vulnerabilities-catalog\" target=\"_blank\">KEV<\/a>) catalog, requiring Federal Civilian Executive Branch (FCEB) agencies to apply the fixes by June 3, 2026.<\/p>\n<p>With the latest development, a total of three Microsoft vulnerabilities have been flagged as exploited within a span of a week. Last week, Redmond disclosed that a cross-site scripting flaw impacting on-premise versions of Exchange Server (CVE-2026-42897, CVSS score: 8.1) had been weaponized in real-world attacks.<\/p>\n<div class=\"dog_two clear\">\n<div class=\"cf\"><a href=\"https:\/\/thehackernews.uk\/ai-cant-stop-d\" rel=\"nofollow noopener sponsored\" target=\"_blank\"><img loading=\"lazy\" decoding=\"async\" class=\"lazyload\" alt=\"Cybersecurity\" src=\"https:\/\/blogger.googleusercontent.com\/img\/b\/R29vZ2xl\/AVvXsEjPEV6-530TOlxG6PjrmdlY623wpBwduZ7t1HV6flcmO5R4q4AmfixDUzW0CrhlvMVNWbhvOIso-UDNTka4W_W9Chrdj_dglwBZwi7DuePM2IMIl-hfUYVIqBXgfpr_2619K8Gptb4LzwJ6gUbi7lWl2M8AFQJsHEaw63Q7tZ6708YGruiHrr0Y2W9YYxLQ\/s728-e100\/ThreatLocker-d.png\" width=\"729\" height=\"91\"\/><\/a><\/div>\n<\/div>\n<p>Also added to the KEV catalog on Wednesday are four other Microsoft flaws from 2008, 2009, and 2010 &#8211;<\/p>\n<ul>\n<li><b><a href=\"https:\/\/nvd.nist.gov\/vuln\/detail\/CVE-2010-0806\" target=\"_blank\">CVE-2010-0806<\/a><\/b> &#8211; Microsoft Internet Explorer contains a use-after-free vulnerability that could allow remote attackers to execute arbitrary code.<\/li>\n<li><b><a href=\"https:\/\/nvd.nist.gov\/vuln\/detail\/CVE-2010-0249\" target=\"_blank\">CVE-2010-0249<\/a><\/b> &#8211; Microsoft Internet Explorer contains a use-after-free vulnerability that could allow remote attackers to execute arbitrary code.<\/li>\n<li><b><a href=\"https:\/\/nvd.nist.gov\/vuln\/detail\/CVE-2009-1537\" target=\"_blank\">CVE-2009-1537<\/a><\/b> &#8211; Microsoft DirectX contains a NULL byte overwrite vulnerability in the QuickTime Movie Parser Filter in quartz.dll in DirectShow, which could allow remote attackers to execute arbitrary code via a crafted QuickTime media file.<\/li>\n<li><b><a href=\"https:\/\/nvd.nist.gov\/vuln\/detail\/cve-2008-4250\" target=\"_blank\">CVE-2008-4250<\/a><\/b> &#8211; Microsoft Windows contains a buffer overflow vulnerability in the Windows Server Service that allows remote attackers to execute arbitrary code via a crafted RPC request.<\/li>\n<\/ul>\n<p>Another vulnerability that finds a mention in the list is <b><a href=\"https:\/\/nvd.nist.gov\/vuln\/detail\/CVE-2009-3459\" target=\"_blank\">CVE-2009-3459<\/a><\/b>, a heap-based buffer overflow vulnerability in Adobe Acrobat and Reader that could allow remote attackers to execute arbitrary code via a crafted PDF file that triggers memory corruption.<\/p>\n<\/div>\n","protected":false},"excerpt":{"rendered":"<p>\ue804Ravie Lakshmanan\ue802May 21, 2026Endpoint Security \/ Vulnerability Microsoft has disclosed that a privilege escalation and a denial-of-service flaw in Defender has come under active exploitation in the wild. The former,&hellip;<\/p>\n","protected":false},"author":1,"featured_media":1004,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[201,1246,128,147,474,148],"class_list":["post-1003","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-uncategorized","tag-actively","tag-defender","tag-exploited","tag-microsoft","tag-vulnerabilities","tag-warns"],"_links":{"self":[{"href":"https:\/\/thedigitalfortress.us\/index.php?rest_route=\/wp\/v2\/posts\/1003","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/thedigitalfortress.us\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/thedigitalfortress.us\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/thedigitalfortress.us\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/thedigitalfortress.us\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=1003"}],"version-history":[{"count":0,"href":"https:\/\/thedigitalfortress.us\/index.php?rest_route=\/wp\/v2\/posts\/1003\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/thedigitalfortress.us\/index.php?rest_route=\/wp\/v2\/media\/1004"}],"wp:attachment":[{"href":"https:\/\/thedigitalfortress.us\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=1003"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/thedigitalfortress.us\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=1003"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/thedigitalfortress.us\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=1003"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}