CVE-2026-70096 in Office 365 for Mac
Summary
by MITRE • 10/14/2026
Heap-based buffer overflow in Windows Rich Text Edit Control allows an unauthorized attacker to execute code over a network.
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Analysis
by VulDB Data Team • 10/14/2026
The vulnerability described involves a heap-based buffer overflow within the Microsoft Windows Rich Text Edit Control, commonly referred to as RICHED20.DLL or similar variants depending on the specific version of the operating system and installed updates. This component is responsible for rendering rich text content in various applications that support formatted documents, such as word processors, email clients, and web browsers utilizing embedded controls. The core technical flaw lies in how the control processes specially crafted input data without adequate bounds checking or validation mechanisms. When an attacker provides a maliciously constructed document or HTML payload containing oversized fields or malformed structures, the application allocates memory on the heap to store this information but fails to verify that the incoming data fits within the allocated buffer boundaries. Consequently, excess data overwrites adjacent memory locations, corrupting critical data structures such as function pointers, object headers, or exception handling records stored in the same memory region.
This type of vulnerability is classified under CWE-122: Heap-based Buffer Overflow, which represents a significant risk because heap corruption can lead to arbitrary code execution with varying degrees of privilege depending on the context in which the vulnerable application runs. The operational impact is severe, as it allows an unauthorized attacker to execute arbitrary code over a network by tricking a user into opening a malicious file or visiting a compromised website that hosts exploit code. Unlike stack-based overflows, heap-based exploits often require more sophisticated techniques such as heap spraying or using specific allocation patterns to reliably achieve control flow hijacking. However, once the memory corruption is achieved and execution flow is redirected, the attacker can gain full control of the affected process, potentially leading to complete system compromise if the application runs with elevated privileges or if additional vulnerabilities are chained together to escalate privileges further.
From a threat intelligence perspective, this vulnerability aligns with MITRE ATT&CK techniques related to Initial Access via Spearphishing Attachment (T1566) and Execution via User Interaction (T1204), particularly when the attack vector involves convincing users to open malicious documents or click on links that trigger the rendering of the vulnerable control. It also relates to Defense Evasion through Obfuscated Files or Information if attackers use packing techniques to hide the exploit payload within seemingly benign files. The ability to execute code over a network makes this vulnerability attractive for automated exploitation campaigns, where bots scan for systems running susceptible versions of Windows and deliver payloads without requiring physical access or local user interaction beyond opening an email attachment or viewing a webpage.
Mitigation strategies primarily focus on applying vendor-supplied security patches that address the input validation flaws within the Rich Text Edit Control. Organizations should ensure that all workstations are updated with the latest cumulative updates from Microsoft, which typically include fixes for such memory corruption vulnerabilities in core system libraries. Additionally, implementing application whitelisting policies can restrict the execution of untrusted binaries or scripts launched by compromised applications, thereby limiting the impact even if an exploit succeeds. Network segmentation and strict e-mail filtering rules that block potentially dangerous file types like .docx with macros or embedded objects from external sources also serve as effective defensive measures. Users should be educated to exercise caution when opening documents from unknown senders and to disable automatic previewing of rich text content in email clients where possible, reducing the attack surface by preventing the vulnerable control from processing untrusted input automatically.