CVE-2026-56645: Microsoft Edge Chromium Buffer Overflow

CVE-2026-56645 Overview

CVE-2026-56645 is a heap-based buffer overflow [CWE-122] in Microsoft Edge (Chromium-based) that enables remote code execution over a network. An unauthenticated attacker can exploit the flaw by convincing a targeted user to interact with malicious web content. Successful exploitation results in code execution in the context of the browser process, with high impact on confidentiality, integrity, and availability.

Critical Impact
A remote attacker can execute arbitrary code on affected systems when a user visits attacker-controlled web content, compromising the browser session and potentially the underlying host.

Affected Products

Microsoft Edge (Chromium-based) — all versions prior to the fixed release referenced in the Microsoft Security Update Guide
Deployments across Windows, macOS, and Linux endpoints running Edge Chromium
Enterprise environments using Edge as the default managed browser

Discovery Timeline

2026-07-03 - CVE-2026-56645 published to NVD
2026-07-07 - Last updated in NVD database

Technical Details for CVE-2026-56645

Vulnerability Analysis

The vulnerability is a heap-based buffer overflow within Microsoft Edge (Chromium-based). Heap overflows occur when code writes data beyond the boundaries of a heap-allocated buffer, corrupting adjacent memory structures. In modern browsers, corrupted heap metadata or object vtables can be leveraged to redirect execution flow.

The attack requires network access and user interaction, meaning a user must load attacker-controlled content such as a crafted webpage, advertisement, or embedded iframe. No authentication or prior privileges on the target are required. Because the scope is unchanged, exploitation compromises the browser process directly, which typically runs with the interactive user's privileges.

Successful exploitation yields high impact across confidentiality, integrity, and availability. An attacker who chains this bug with a sandbox escape can extend control to the host operating system.

Root Cause

The root cause is improper bounds validation on a heap-allocated buffer within Edge's Chromium-based rendering or JavaScript execution stack. When data of an untrusted length is copied into a fixed-size heap region, adjacent chunks and object headers are overwritten. Attackers use heap grooming techniques to place controllable objects next to the vulnerable buffer prior to the overflow.

Attack Vector

The attack vector is network-based through crafted web content. A victim navigating to a malicious page, viewing a compromised ad, or opening a phishing link triggers the vulnerable code path. Refer to the Microsoft Security Update Guide entry for CVE-2026-56645 for vendor-specific technical details and affected builds.

No verified public proof-of-concept code is available at the time of publication. The vulnerability is described in prose only; synthetic exploit code is not provided.

Detection Methods for CVE-2026-56645

Indicators of Compromise

Unexpected msedge.exe child processes spawning command interpreters such as cmd.exe, powershell.exe, or bash
Browser renderer crashes with heap corruption signatures in Windows Error Reporting or crashpad dumps
Outbound connections from the Edge process to previously unseen domains immediately following page navigation
Writes to autorun locations or user profile directories originating from Edge processes

Detection Strategies

Monitor for anomalous process trees where Edge spawns non-browser binaries, a common post-exploitation pattern
Correlate browser crash telemetry with subsequent execution of unsigned binaries from user-writable paths
Inspect proxy and DNS logs for user navigation to newly registered or low-reputation domains preceding crash events

Monitoring Recommendations

Enable enterprise browser telemetry through Microsoft Edge management policies and forward events to the SIEM
Track Edge version inventory across the fleet to identify hosts still running vulnerable builds
Alert on kernel-mode or user-mode memory protection violations attributed to the Edge process

How to Mitigate CVE-2026-56645

Immediate Actions Required

Update Microsoft Edge (Chromium-based) to the fixed version identified in the Microsoft Security Update Guide
Force browser restart across managed endpoints to ensure the patch takes effect
Verify automatic update channels are enabled and reachable from all client networks
Prioritize patching for high-risk users such as executives, developers, and administrators

Patch Information

Microsoft has released a security update addressing CVE-2026-56645. Refer to the Microsoft Security Update Guide for the specific fixed build number and deployment guidance. Edge typically updates automatically, but enterprise-managed installations may require deployment through Microsoft Intune, Configuration Manager, or Group Policy.

Workarounds

Restrict browsing to trusted domains using web content filtering until patching is complete
Enable Microsoft Defender SmartScreen and Enhanced Security Mode in Edge to reduce exposure to untrusted sites
Deploy site isolation and strict Content Security Policy enforcement through browser management policies
Educate users to avoid clicking untrusted links until the update is applied fleet-wide

bash

# Verify installed Edge version on Windows endpoints
reg query "HKLM\SOFTWARE\Microsoft\Edge\BLBeacon" /v version

# Force Edge policy refresh after deploying the update via Group Policy
gpupdate /force