June 2026 Patch Tuesday forecast: Where are the CVEs?

CVE-2026-45498 is a denial-of-service flaw (CWE-400, uncontrolled resource consumption) in the Microsoft Defender antimalware platform, rated 7.5 (High) with a network attack vector and no privileges or user interaction required. A remote, unauthenticated attacker can trigger excessive resource consumption that disrupts the Defender service, with high impact on availability but no confidentiality or integrity impact per the CVSS scoring. An attacker gains the ability to crash, hang, or disable antimalware protection on targeted systems, potentially leaving endpoints temporarily unprotected. Any deployment of Microsoft Defender — which is the default antimalware on modern Windows and is also deployed as a cloud service — is in scope, and CISA's required action explicitly points defenders to BOD 22-01 guidance for cloud services. The flaw has been added to CISA's KEV catalog (2026-05-20), EPSS assigns it a 63.1% probability of exploitation within 30 days, and headlines confirm it is being exploited in the wild alongside CVE-2026-41091.

Do: Apply mitigations per Microsoft's vendor instructions and follow applicable CISA BOD 22-01 guidance for cloud services, as required by the KEV entry. Ensure the Defender antimalware platform and its security intelligence updates are fully current on all endpoints, and check event logs for Defender service crashes or disabled protection that may indicate exploitation. Ransomware use is currently listed as unknown, so treat any Defender outage on exposed systems as a potential precursor to follow-on activity.

CVE-2026-42897 is an improper-neutralization flaw (CWE-79) in Microsoft Exchange Server that lets an unauthenticated remote attacker perform cross-site scripting and carry out spoofing. Per the CVSS vector (AV:N/PR:N/UI:R), exploitation requires a victim to interact with attacker-controlled content — reported attacks by the Russian actor Laundry Bear (TA488) trigger when a crafted email is opened in Exchange's webmail interface (Outlook Web Access). The attacker gains the ability to spoof the victim within their webmail session, and reported intrusions show mailbox access persisting even after organizations rotate credentials. Any organization running on-premises Microsoft Exchange Server or Exchange Server Subscription Edition is potentially exposed, particularly those publishing webmail to the internet; specific affected version ranges are not provided in the available data. Exploitation is confirmed in the wild: the flaw was added to CISA KEV on 2026-05-15 and carries a very high EPSS score of 71.2%, though no public proof-of-concept is known.

Do: Apply Microsoft's security update for CVE-2024-42897 to all on-premises Exchange and Exchange Subscription Edition servers per vendor guidance — no specific patch versions are provided in the available data, so consult the vendor advisory for build numbers. Federal agencies must patch or apply mitigations per BOD 22-01 given the KEV listing. Because reported attacks (Laundry Bear/TA488) maintain mailbox access after password resets, treat any suspected compromise as persistent: review OWA access logs and inbox rules for anomalies, and invalidate active webmail sessions and tokens, not just credentials.

CVE-2026-45659 is a deserialization-of-untrusted-data vulnerability (CWE-502) in Microsoft SharePoint Server in which an authorized (authenticated, low-privilege) attacker can submit crafted serialized data over the network, with no user interaction required, to execute code on the server. Successful exploitation carries high impact on confidentiality, integrity, and availability within the SharePoint service context, giving attackers a foothold for follow-on activity, and CISA notes that ransomware use is known. Organizations running on-premises Microsoft SharePoint Server are affected; the source data lists no specific version ranges, and the CPE scope (sharepoint server) points to the on-premises product rather than the Microsoft-managed SharePoint Online service. The flaw was added to CISA's Known Exploited Vulnerabilities catalog on 2026-07-01 after active exploitation, and its EPSS score of 76.1% (100th percentile) indicates a high probability of near-term exploitation. The CVE record lists no public proof-of-concept, though related reporting describes exploitation activity following a public PoC release for a SharePoint authentication bypass.

Do: Apply Microsoft's current security updates for SharePoint Server following vendor instructions, prioritizing internet-facing servers, and comply with CISA BOD 26-04, which requires applying mitigations per vendor guidance (including the cited Forensics Triage Requirements) or discontinuing use of the product if mitigations are unavailable. Because in-the-wild exploitation and ransomware use are confirmed, triage exposed servers for compromise: review IIS/SharePoint logs for unexpected authenticated requests, look for webshells or newly modified files in SharePoint web roots, and check for unusual child processes spawned by the SharePoint application pool. Given related reporting on an authentication-bypass PoC, also verify that any related SharePoint authentication-bypass patches are…