Multiple Microsoft Exchange Server RCE Flaws Patched Across Supported Releases
Microsoft published security advisories for several Microsoft Exchange Server remote code execution vulnerabilities, including CVE-2021-26427, CVE-2022-21969, CVE-2022-23277, and CVE-2023-36778. The flaws affect on-premises Exchange Server deployments and were addressed through Microsoft's Security Update Guide, indicating a recurring pattern of high-impact code-execution risk in a core enterprise messaging platform.
The advisories show Microsoft issuing fixes over multiple release cycles for distinct Exchange Server RCE bugs rather than a single isolated defect. For defenders, the immediate implication is to verify that all supported Exchange Server instances have the relevant cumulative and security updates applied, because unpatched mail servers remain a high-value target due to their internet exposure, privileged position in enterprise environments, and history of exploitation by threat actors.
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How this story unfolded
4 events from the most recent confirmed update back to the earliest known activity.
Microsoft discloses CVE-2023-36778 in Exchange Server
Microsoft added CVE-2023-36778 to its Security Update Guide as a remote code execution vulnerability affecting Microsoft Exchange Server.
Microsoft discloses CVE-2022-23277 in Exchange Server
Microsoft published Security Update Guide information for CVE-2022-23277, a remote code execution vulnerability impacting Microsoft Exchange Server.
Microsoft discloses CVE-2022-21969 in Exchange Server
Microsoft released a Security Update Guide advisory for CVE-2022-21969, identifying it as a remote code execution vulnerability in Microsoft Exchange Server.
Microsoft discloses CVE-2021-26427 in Exchange Server
Microsoft published security guidance for CVE-2021-26427, a remote code execution vulnerability affecting Microsoft Exchange Server.
Sources
4 references tracked. Mallory keeps watching after this page renders.
CVE-2023-36778 - Security Update Guide - Microsoft - Microsoft Exchange Server Remote Code Execution Vulnerability
msrc.microsoft.com
Open sourceCVE-2022-23277 - Security Update Guide - Microsoft - Microsoft Exchange Server Remote Code Execution Vulnerability
msrc.microsoft.com
Open sourceCVE-2022-21969 - Security Update Guide - Microsoft - Microsoft Exchange Server Remote Code Execution Vulnerability
portal.msrc.microsoft.com
Open sourceCVE-2021-26427 - Security Update Guide - Microsoft - Microsoft Exchange Server Remote Code Execution Vulnerability
msrc.microsoft.com
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Microsoft has disclosed multiple **elevation of privilege** vulnerabilities affecting **Microsoft Exchange Server**, including `CVE-2021-34470`, `CVE-2021-41348`, `CVE-2022-41123`, and `CVE-2025-64666`, indicating a recurring security issue in the on-premises mail platform across several release cycles. The advisories show Exchange continued to receive fixes for privilege-escalation weaknesses over multiple years, with Microsoft publishing separate Security Update Guide entries as new flaws were identified. Among the listed issues, Microsoft provided the most detail for `CVE-2021-34470`, rating it **Important** with a **CVSS 3.0 score of 8.0** and describing it as requiring access from a logically adjacent network. Microsoft said the flaw required a **schema change** and was fixed for **Exchange Server 2019** and **Exchange Server 2016** in cumulative updates released on June 29, 2021; at initial publication, the company said it was **not publicly disclosed**, **not exploited**, and **less likely to be exploited**. A separate Microsoft advisory in the same reference set, `CVE-2026-26128`, affects the **Windows SMB Server** rather than Exchange and also involves elevation of privilege.
May 25, 2026
Microsoft Patches Exchange Server RCE Vulnerability CVE-2021-31196
Microsoft disclosed and patched **CVE-2021-31196**, a remote code execution vulnerability in **Microsoft Exchange Server**. The company rated the flaw **Important** and assigned it a **CVSS 3.0 score of 7.2**, with the vector `AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:H`, indicating the issue is reachable over the network, requires no user interaction, and could lead to high impact across confidentiality, integrity, and availability if successfully exploited. Microsoft said the vulnerability required **high privileges**, assessed exploitation as **less likely**, and reported that exploit code was **unproven** and that the flaw was **not publicly disclosed or actively exploited** at the time of publication. An official security update was made available through the Microsoft Security Response Center, and Microsoft credited **Orange Tsai of DEVCORE** with reporting the issue.
May 25, 2026
Microsoft Exchange Server Spoofing Flaws Tracked Across Multiple CVEs
Microsoft has published Security Update Guide entries for multiple **Microsoft Exchange Server spoofing vulnerabilities**, including `CVE-2021-1730`, `CVE-2024-49040`, and `CVE-2025-64667`. The references indicate a recurring class of flaws affecting Exchange Server in which an attacker could impersonate a trusted source or manipulate how identities or messages are presented, creating opportunities for phishing, fraud, or follow-on compromise in enterprise email environments. The available advisories provide limited public technical detail, but the repeated publication of Exchange spoofing CVEs shows that Microsoft continues to track and remediate this attack surface through its update program. For defenders, the immediate implication is to review Exchange Server exposure, validate that relevant Microsoft security updates tied to these CVEs have been applied, and monitor mail infrastructure for signs of spoofed communications or abuse of trust relationships involving Exchange services.
May 25, 2026