CVE-2025-24081 - Use-After-Free in Microsoft Excel Leads to Remote Code Execution

Microsoft Excel is one of the world’s most popular spreadsheet applications, found on millions of computers. Sometimes, bugs in software can have critical consequences. One such bug is a security vulnerability called a "use-after-free". In this post, we’ll break down CVE-2025-24081—a fresh vulnerability in Microsoft Office Excel—explain how it works, show how attackers can exploit it, and provide resources for staying safe.

What is CVE-2025-24081?

CVE-2025-24081 is the identifier for a use-after-free vulnerability discovered in Microsoft Excel for Office (including Excel 2021 and Microsoft 365 versions). When certain crafted files are opened, Excel mistakenly allows access to memory it has already freed—memory that might be replaced with malicious code. This flaw allows an attacker to execute code on the victim’s machine and potentially take full control.

Severity: High
Attack Vector: Local (requires tricking a user into opening an infected file)
Impact: Remote code execution under the current user’s permissions

How Does Use-After-Free Work in Excel?

A use-after-free bug happens when the program "frees" (or releases) memory, but still tries to use that part of memory. If an attacker can influence what’s put in the freed memory, he or she can trick Excel into running code of their choosing.

Simple Example Code

Below is a heavily simplified pseudocode showing the use-after-free concept (not the real Excel code, but in spirit):

Cell* cell = allocateCell();
free(cell); // The memory is released

cell->setValue("attacker data"); // Excel tries to use it after freeing

In real Excel, the details are more complex, but figured around similar logic: Excel may deallocate a structure (such as a cell or formula object), but due to flawed logic, it may still reference the pointer, giving attackers a chance to redirect execution via crafted content.

Proof of Concept (Simulated)

Attackers may craft an Excel file with unusual shared formulas or malformed XML that triggers the bug:

<cell r="A1" t="s">
  <v>malicious input here</v>
</cell>

Opening such a file can cause Excel to access freed memory, leading to arbitrary code execution if the memory is replaced with shellcode.

Real-World Impact

Suppose you receive a spreadsheet from an unknown sender and open it. The spreadsheet is engineered to exploit CVE-2025-24081. Behind the scenes, Excel’s memory corruption lets the file's payload run, installing malware or ransomware, stealing documents, or giving access to internal networks. This could fully compromise your machine unless protected.

Step-by-step attack (simplified)

1. Prepare malicious file: The attacker creates an Excel file with a crafted payload exploiting the use-after-free.

Execute payload: Attacker gains code execution privilege—often as the current user.

Mitre Reference:
- CVE-2025-24081 on MITRE
- Microsoft Security Advisory

Protection and Mitigation

- Update Excel: Install the latest Microsoft Office security updates (Microsoft Guidance).

Open files cautiously: Don’t open unknown or unexpected files, especially from email.

- Use Protected View: Excel’s Protected View helps block these exploits—but not if macros are enabled.

Summary

CVE-2025-24081 is a major reminder: even trusted apps like Excel can have deeply buried bugs that let attackers run code on your computer. Always patch promptly, exercise caution with documents, and use security tools to stay safe.

If you’re interested in technical writeups, check out

- Microsoft Technical Details (MSRC)
- NIST National Vulnerability Database Entry

Timeline

Published on: 03/11/2025 17:16:32 UTC
Last modified on: 04/03/2025 21:15:03 UTC