CVE-2026-42831 Heap-based Buffer Overflow in Microsoft Office

CVE-2026-42831 is a heap-based buffer overflow vulnerability affecting Microsoft Office. This vulnerability allows an attacker with local access to execute arbitrary code. The vulnerability arises due to improper memory management when processing specific file formats, leading to a buffer overflow condition in the heap. An attacker could potentially exploit this vulnerability by crafting a malicious file and enticing a user to open it with a vulnerable version of Microsoft Office. Successful exploitation could allow the attacker to gain full control over the affected system. The CVE was published on May 12, 2026.

Attack Chain

1. An attacker crafts a malicious Office document (e.g., Word, Excel, PowerPoint) specifically designed to trigger the heap-based buffer overflow.
2. The attacker uses social engineering to convince a user to open the malicious document. This could involve sending the document as an email attachment or hosting it on a website.
3. The user opens the malicious document using a vulnerable version of Microsoft Office.
4. Microsoft Office attempts to process the malformed data within the document, leading to a heap-based buffer overflow.
5. The overflow corrupts adjacent memory regions in the heap, potentially overwriting critical data structures or function pointers.
6. The attacker leverages the memory corruption to redirect program execution to attacker-controlled code.
7. The attacker’s code executes within the context of the Microsoft Office process.
8. The attacker gains local code execution, potentially leading to full system compromise.

Impact

Successful exploitation of CVE-2026-42831 allows a local attacker to execute arbitrary code on a vulnerable system. This could lead to complete system compromise, including data theft, malware installation, and further lateral movement within the network. Due to the widespread use of Microsoft Office, this vulnerability poses a significant risk to organizations and individuals.

Recommendation

• Apply the security update provided by Microsoft to patch CVE-2026-42831 as soon as possible (reference: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-42831).
• Deploy the Sigma rule “Detect CVE-2026-42831 Exploitation Attempt via Suspicious Office Process” to detect potential exploitation attempts.
• Educate users on the risks of opening unsolicited attachments or files from untrusted sources to mitigate the initial attack vector.