Microsoft Patch Tuesday for February 2023 — Snort rules and prominent vulnerabilities

CVE-2023-21529 is a deserialization-of-untrusted-data flaw (CWE-502) in on-premises Microsoft Exchange Server that allows remote code execution. Per its CVSS vector, an attacker with valid low-privileged credentials (PR:L) sends crafted untrusted serialized data to the server over the network, requiring no user interaction. Successful exploitation yields code execution on the Exchange server, exposing mail stores and providing a foothold for lateral movement, and related coverage ties it to the fast-moving Storm-1175 ransomware operation, with ransomware use listed as known in CISA's KEV entry. Organizations running self-hosted Exchange Server are in scope; the source data does not list specific affected builds, but the fix shipped in Microsoft's February 2023 Patch Tuesday updates. The flaw was added to CISA's Known Exploited Vulnerabilities catalog on 2026-04-13, EPSS estimates a 62.1% probability of exploitation within 30 days (99th percentile), and no public proof-of-concept is known.

Do: Apply the February 2023 Exchange Server security updates to every on-premises Exchange server; U.S. federal agencies must mitigate or patch per BOD 22-01 following the KEV listing. Because exploitation requires authenticated low-privilege access, inventory exposed OWA/ECP endpoints, review and rotate credentials, and hunt for compromise indicators (unusual processes, webshells, unexpected mailbox activity) given known ransomware use.

Microsoft Protected Extensible Authentication Protocol (PEAP) Remote Code Execution Vulnerability

Microsoft Office Publisher contains a security feature bypass (CWE-863, incorrect authorization) in which a specially crafted Publisher document can circumvent an Office security mechanism, widely reported as a bypass of the Mark-of-the-Web/Protected View protections applied to files from untrusted sources. The flaw is triggered locally when a user opens the malicious document, consistent with the CVSS vector (local attack, low privileges, user interaction required). Successful bypassing yields high impact on the victim system, with high ratings for confidentiality, integrity, and availability. Anyone running Microsoft 365 Apps or Microsoft Office editions that include Publisher is affected, and no specific affected version numbers are published in this data beyond the requirement to apply the February 2023 fixes. The vulnerability is actively exploited: it was added to CISA's Known Exploited Vulnerabilities catalog on 2023-02-14 and was patched as one of three exploited zero-days in Microsoft's February 2023 Patch Tuesday.

Do: Apply Microsoft's February 2023 Patch Tuesday security updates to Microsoft 365 Apps and any Office edition that includes Publisher, per vendor instructions as required by the CISA KEV entry; because affected builds differ by update channel, confirm the installed build after updating rather than relying on the date alone. Until patched, exercise caution with Publisher documents from untrusted sources. No public PoC or workaround is documented, so patching is the primary mitigation.

Windows iSCSI Discovery Service Remote Code Execution Vulnerability

.NET and Visual Studio Remote Code Execution Vulnerability

Visual Studio Remote Code Execution Vulnerability

CVE-2023-23376 is a heap-based buffer overflow (out-of-bounds write, CWE-122/CWE-787) in the Windows Common Log File System (CLFS) kernel driver. A local attacker with low privileges can trigger the flaw when the driver mishandles CLFS log-file data, with no user interaction required. Successful exploitation elevates the attacker from a low-privileged user to SYSTEM/kernel-level privileges, which is why ransomware operators chain it with other bugs after gaining an initial foothold. All supported Windows 10 (1507, 1607, 1809, 20H2, 21H2, 22H2), Windows 11 (21H2, 22H2), and Windows Server 2008, 2012, 2016, and 2019 releases as of February 2023 are affected. The flaw is actively exploited in the wild: it was added to CISA's Known Exploited Vulnerabilities catalog on February 14, 2023 with known ransomware use, Microsoft shipped the fix in the February 2023 Patch Tuesday release, and EPSS estimates roughly an 11% probability of exploitation within the next 30 days (96th percentile).

Do: Apply the Microsoft security updates released on February 14, 2023 (February Patch Tuesday) to every Windows 10, Windows 11, and Windows Server system in the affected version list, prioritizing servers and endpoints exposed to ransomware-prone environments. Verify patch status via update history or vulnerability scanning, since exploitation requires only local low-privileged access and there is no substitution for patching. Given confirmed ransomware chaining, also hunt for signs of post-compromise privilege escalation on hosts that were unpatched before mid-February 2023.