CVE-2026-77504 in Office
Summary
by MITRE • 09/09/2026
Double free in Microsoft Office Word allows an unauthorized attacker to execute code over a network.
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Analysis
by VulDB Data Team • 09/09/2026
The vulnerability described involves a critical memory management error within the Microsoft Office Word application, specifically classified as a double-free condition. This type of flaw occurs when a program attempts to deallocate or release a block of memory that has already been freed by a previous operation. In the context of complex software like word processors, which handle intricate document structures and embedded objects, such errors can arise from improper handling of pointers during the parsing of maliciously crafted files. When an attacker provides a specially constructed Word document containing malformed data or specific object configurations, they can trigger this double-free sequence within the application's memory space. The immediate technical consequence is often heap corruption, where the internal metadata used by the operating system to manage dynamic memory allocation becomes inconsistent. This state of instability creates a window of opportunity for an attacker to manipulate how subsequent memory allocations are handled, potentially overwriting adjacent data structures or control flow pointers with malicious values.
From an operational perspective, this vulnerability poses a severe risk because it allows for remote code execution without requiring user interaction beyond opening the file, depending on the specific configuration and security settings in place. An unauthorized attacker can exploit this flaw to execute arbitrary commands on the victim's system with the privileges of the currently logged-in user. This capability effectively compromises the confidentiality, integrity, and availability of the affected system. The exploitation chain typically involves crafting a document that triggers the double-free condition during rendering or parsing, leading to heap spray techniques where shellcode is placed in predictable memory locations. Once control flow is redirected to this malicious code, the attacker gains full administrative access to the compromised machine, enabling further lateral movement within a network environment and potential exfiltration of sensitive data stored on the endpoint.
This vulnerability aligns with Common Weakness Enumeration (CWE) category CWE-415, which defines Double Free as releasing memory that has already been freed. It also relates closely to CWE-787, Out-of-bounds Write, as heap corruption often leads to writing beyond allocated boundaries due to the corrupted state of memory management structures. In terms of offensive security frameworks such as MITRE ATT&CK, this exploitation technique falls under T1203, Exploitation for Client Execution, and specifically leverages techniques associated with Memory Corruption (T1254). The attack vector is typically classified as Network-based if the malicious document is delivered via email or a shared network drive, making it part of broader social engineering campaigns where users are tricked into opening infected documents.
Mitigation strategies for this vulnerability primarily involve applying vendor-provided security patches that address the memory management logic within Word to ensure proper reference counting and pointer validation before deallocation operations occur. Organizations should enforce strict email filtering policies to block or quarantine suspicious attachments, particularly those from unknown senders or containing executable content embedded in documents. Additionally, enabling Protected View for files originating from the internet can prevent active code execution until the user explicitly trusts the document. Regular patch management cycles are essential to ensure that systems running Microsoft Office remain updated with the latest security fixes addressing known memory corruption flaws. Network segmentation and endpoint detection and response (EDR) solutions can also help detect anomalous behavior indicative of exploitation attempts, such as unusual process creation or memory access patterns following the opening of a document.