CVE-2026-26134: microsoft 365_copilot Integer Overflow or Wraparound

Vulnerability summary

CVE-2026-26134 is a high (CVSS 7.8) Integer Overflow or Wraparound vulnerability in microsoft 365_copilot. EPSS estimates a 0.35% chance of exploitation in the next 30 days, higher than 26.7% of scored vulnerabilities.

Timeline

1. 10-03-2026
   PublishedVulnerability first disclosed.
2. 19-06-2026
   Last modifiedVulnerability information updated.

Description

Integer overflow or wraparound in Microsoft Office allows an authorized attacker to elevate privileges locally.

• CWE-190Integer Overflow or WraparoundThe product performs a calculation that can produce an integer overflow or wraparound when the logic assumes that the resulting value will always be larger than the original value. This occurs when an integer value is incremented to a value that is too large to store in the associated representation. When this occurs, the value may become a very small or negative number.
• CWE-416Use After FreeThe product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory "belongs" to the code that operates on the new pointer.