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CISA added two newly tracked flaws to its Known Exploited Vulnerabilities (KEV) catalog: CVE-2026-20963 in Microsoft SharePoint and CVE-2025-66376 in Synacor Zimbra Collaboration Suite. The SharePoint issue is a deserialization of untrusted data vulnerability, mapped to CWE-502, that can allow code execution over the network; CISA’s KEV entry describes it as enabling an unauthorized attacker to execute code remotely. The Zimbra issue is a stored cross-site scripting flaw in the Classic UI, mapped to CWE-79, in which attackers can abuse CSS @import directives in email HTML.
CISA’s KEV update requires federal civilian executive branch agencies to remediate the SharePoint flaw by 2026-03-21 and the Zimbra flaw by 2026-04-01, or follow applicable mitigation guidance under BOD 22-01. The GitHub KEV data commit confirms both additions and records the required actions as applying vendor mitigations, following cloud-service guidance where relevant, or discontinuing use if mitigations are unavailable. The reporting also notes that, while the KEV catalog is binding on federal agencies, private organizations should review the catalog and prioritize these vulnerabilities because CISA has identified them as actively exploited.
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6 events from the most recent confirmed update back to the earliest known activity.
Seqrite Labs said exploitation of Zimbra Collaboration Suite flaw CVE-2025-66376 was tied to Operation GhostMail, a suspected Russian state-sponsored campaign. The activity reportedly targeted the State Hydrographic Service of Ukraine via a malicious HTML email used to steal credentials, session tokens, 2FA recovery codes, browser passwords, and mailbox contents.
CISA said CVE-2026-20963, a critical SharePoint remote code execution flaw, is being actively exploited against unpatched servers. Reporting noted Microsoft had updated its advisory, while CISA said it had not found evidence of ransomware-related exploitation.
After adding CVE-2026-20963 and CVE-2025-66376 to the KEV catalog, CISA directed Federal Civilian Executive Branch agencies to patch the SharePoint flaw by March 21, 2026 and the Zimbra flaw by April 1, 2026. CISA also advised organizations to review the KEV catalog and apply vendor mitigations.
CISA added five newly listed Known Exploited Vulnerabilities affecting Microsoft SharePoint, Synacor Zimbra Collaboration Suite, Wing FTP Server, and Google Chromium/Skia components. The additions were reflected in the KEV data update published on March 18, 2026.
According to Amazon, threat actors linked to the Interlock ransomware operation started exploiting Cisco firewall management software zero-day CVE-2026-20131 before it was publicly disclosed. The activity reportedly began on January 26, 2026.
Microsoft released a fix for CVE-2026-20963, a deserialization of untrusted data vulnerability in SharePoint Server that can allow unauthenticated remote code execution. Later reporting states the flaw was patched in January 2026.
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**CISA** added **CVE-2026-20963**, a **Microsoft SharePoint** deserialization flaw, to its **Known Exploited Vulnerabilities (KEV)** catalog after confirming active exploitation in the wild. The vulnerability allows an **unauthorized remote attacker** to execute arbitrary code over the network by sending crafted serialized data that SharePoint improperly deserializes, creating a **pre-authentication remote code execution** path. Reporting indicates the specific threat actors behind the attacks have not been publicly identified, but the flaw affects a widely deployed enterprise collaboration platform that often stores sensitive internal documents and communications. The KEV entry triggered urgent remediation requirements, including a **March 21, 2026** deadline for **FCEB agencies** under **Binding Operational Directive 22-01**. Additional reporting notes that the same KEV update also included vulnerabilities in **Wing FTP Server** and **Synacor Zimbra Collaboration Suite**, but the SharePoint issue stands out because of its likely value for **initial access brokers** and **ransomware affiliates** seeking enterprise footholds. Organizations using SharePoint should treat internet-exposed systems as high priority for patching and review for signs of compromise given confirmed in-the-wild exploitation.
Jun 29, 2026
**CISA** added **CVE-2025-66376** to its **Known Exploited Vulnerabilities (KEV)** catalog after confirming active exploitation of a **stored cross-site scripting (XSS)** flaw in **Synacor Zimbra Collaboration Suite (ZCS)**. The vulnerability affects the *Classic UI* and allows remote unauthenticated attackers to abuse CSS `@import` directives embedded in email HTML, creating a path to execute malicious JavaScript in a victim's browser session. The KEV entry describes the issue as a **CWE-79** XSS vulnerability and directs organizations to apply vendor mitigations, follow **BOD 22-01** guidance for cloud services, or discontinue use if mitigations are unavailable. CISA ordered **Federal Civilian Executive Branch (FCEB)** agencies to remediate the flaw by **April 1**, while also urging private-sector organizations to patch quickly because the bug is being exploited in the wild. Reporting on the KEV addition notes that the flaw was patched by Zimbra earlier and could enable session hijacking and theft of sensitive data within affected Zimbra environments through malicious HTML email content. The same KEV update also included other unrelated vulnerabilities, but the Zimbra entry is the relevant event tied to the active exploitation warning and federal patching directive.
Jun 29, 2026
CISA added **`CVE-2026-45659`** to its Known Exploited Vulnerabilities catalog after confirming active exploitation of a high-severity remote code execution flaw in on-premises **Microsoft SharePoint Server**. The vulnerability stems from **deserialization of untrusted data** (`CWE-502`) and carries a **CVSS 8.8** score. It affects **SharePoint Enterprise Server 2016**, **SharePoint Server 2019**, and **SharePoint Server Subscription Edition** below patched versions, and can be exploited over the network by an authenticated attacker with low privileges such as **Site Member**, without user interaction. Microsoft issued fixes in its **May 2026** security updates, later clarifying that the CVE had been inadvertently omitted from the initial update list. CISA set a **July 4, 2026** remediation deadline for federal civilian agencies under Binding Operational Directive 22-01, while public reporting said the exact vulnerable SharePoint component, gadget chain, payload delivery method, and any connection to ransomware activity had not yet been disclosed. Security guidance accompanying the KEV listing urged organizations to patch immediately and review exposed SharePoint environments for signs of compromise.
Jul 10, 2026