Critical Microsoft Office Vulnerabilities Enable Malicious Code Execution

Microsoft has addressed three critical security flaws in its Office suite, including two vulnerabilities rated Critical and one Important, all enabling remote code execution (RCE) via use-after-free memory corruption weaknesses.

These vulnerabilities, disclosed between March and May 2025, expose systems to attacks where malicious actors could execute arbitrary code by enticing users to open specially crafted documents.

While none have been actively exploited, the severity of these flaws underscores the need for immediate patching.

The most severe vulnerabilities, CVE-2025-30377 and CVE-2025-30386, both carry a CVSSv3.1 score of 8.4 (7.3 environmental).

These flaws reside in how Microsoft Office handles memory objects, allowing attackers to manipulate freed memory pointers to execute code.

The attack vector requires no user interaction beyond opening a malicious document, as both flaws operate via the AV:L/AC:L/PR:N/UI:N vector.

Despite their identical CVSS metrics, their exploitability differs significantly.

Microsoft assesses CVE-2025-30377 as “Exploitation Less Likely” due to inherent memory layout randomization in modern Office versions, while CVE-2025-30386 is labeled “Exploitation More Likely” because of predictable memory structures in older file formats like DOC and XLS.

Security researchers note that combining these flaws with social engineering could bypass Office’s Protected View, a common defense against document-based attacks.

User Interaction Requirement

The third vulnerability, CVE-2025-26629, rated 7.8 on the CVSS scale, introduces a user interaction requirement (UI:R) that slightly reduces its risk profile.

Attackers must trick users into enabling macros or embedded content after document opening, a tactic often paired with phishing campaigns.

This flaw affects Office’s dynamic data exchange (DDE) component, which has historically been a target for advanced persistent threat groups.

Microsoft patched CVE-2025-26629 in March 2025 but revised its advisory in May to reflect new exploit chain possibilities involving Excel’s Power Query.

While its lower severity score reflects the added user interaction hurdle, security teams warn that it remains a viable entry point for targeted attacks, particularly against organizations with lax macro policies.

Mitigation Strategies and Patch Deployment

Microsoft has released updates via its May 2025 Patch Tuesday cycle for CVE-2025-30377 and CVE-2025-30386, while CVE-2025-26629’s fix was distributed in March.

Enterprises are advised to:

1. Prioritize patching endpoints running Office 2019 and Microsoft 365 Apps, which contain the memory management improvements needed to mitigate these flaws.
2. Enforce application hardening by blocking Office child processes and restricting macro execution via Group Policy.
3. Monitor for exploit chains combining these CVEs with privilege escalation vulnerabilities, a common tactic in ransomware deployments.

While no public exploit code exists, the similarities between these flaws and previously weaponized use-after-free vulnerabilities suggest proof-of-concept development is imminent.

Microsoft’s Threat Intelligence Center (MSTIC) has observed increased scanning activity for unpatched Office instances in the past 72 hours, indicating potential reconnaissance phases of attacks.

Administrators should treat these vulnerabilities as critical infrastructure risks, given Office’s ubiquitous presence in enterprise environments.

The combination of silent exploitation vectors and high-impact outcomes positions these flaws as prime targets for advanced cybercriminal operations.

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