CVE-2025-21408: Microsoft Edge Chromium RCE Vulnerability

CVE-2025-21408 Overview

CVE-2025-21408 is a remote code execution vulnerability in Microsoft Edge (Chromium-based). The flaw is classified under [CWE-843] Type Confusion, where the browser interprets a resource as a different type than originally allocated. An attacker who hosts a specially crafted web page can trigger the condition when a victim visits the site, leading to code execution within the browser process context.

The vulnerability requires user interaction, typically through navigation to attacker-controlled content. Microsoft published the advisory on February 6, 2025, and assigned it a high severity rating.

Critical Impact
Successful exploitation allows attackers to execute arbitrary code in the context of the current user, compromising confidentiality, integrity, and availability of the browser session.

Affected Products

Microsoft Edge (Chromium-based) — versions prior to the February 2025 security update
Windows installations running vulnerable Edge builds
macOS installations running vulnerable Edge builds

Discovery Timeline

2025-02-06 - CVE-2025-21408 published to NVD
2025-02-11 - Last updated in NVD database

Technical Details for CVE-2025-21408

Vulnerability Analysis

The vulnerability stems from a type confusion condition [CWE-843] in the Chromium engine that underpins Microsoft Edge. Type confusion occurs when code allocates a resource using one type definition but later accesses it using an incompatible type. The mismatch lets attackers manipulate memory layouts and object pointers that the browser treats as trusted.

In JavaScript engines and rendering pipelines, type confusion frequently surfaces in just-in-time (JIT) compilers, garbage collection paths, or object property handlers. The engine assumes one structure but operates on attacker-controlled data, enabling reads or writes outside expected boundaries. Attackers can pivot this primitive into arbitrary code execution within the browser sandbox.

The network attack vector and low complexity make this flaw broadly accessible to attackers. User interaction is required, so exploitation depends on social engineering, malvertising, or compromised legitimate sites.

Root Cause

The root cause is improper type validation inside the Chromium-based rendering or scripting subsystem used by Microsoft Edge. The code path operates on an object under an assumed type without verifying the actual runtime type. This mismatch allows an attacker to control memory contents and corrupt internal browser structures.

Attack Vector

An attacker hosts a malicious web page containing JavaScript designed to trigger the type confusion. The victim visits the page through Edge, either directly or via a redirect from a compromised site, phishing link, or malicious advertisement. The crafted payload manipulates object types during script execution, leading to memory corruption and remote code execution within the user's security context.

No verified proof-of-concept code is publicly available. The technical mechanism is described in prose based on the assigned CWE classification. Refer to the Microsoft CVE-2025-21408 Advisory for vendor-confirmed details.

Detection Methods for CVE-2025-21408

Indicators of Compromise

Unexpected child processes spawned by msedge.exe, particularly command interpreters such as cmd.exe or powershell.exe
Outbound network connections from Edge renderer processes to unfamiliar domains or IP addresses
Browser crash dumps referencing renderer process faults coinciding with visits to untrusted sites
Creation of executable files in user-writable directories shortly after browsing activity

Detection Strategies

Monitor process lineage for anomalous descendants of msedge.exe and correlate with recent navigation events
Inspect endpoint telemetry for memory protection violations or exploit mitigation alerts originating from Edge processes
Apply behavioral analytics to flag scripted execution chains initiated from browser-spawned processes
Track installed Edge versions across the fleet and alert on hosts running builds prior to the February 2025 patch

Monitoring Recommendations

Forward browser process telemetry, including command-line arguments and child process events, to a centralized analytics platform
Enable web filtering and DNS monitoring to identify navigation to known malicious or newly registered domains
Audit Edge update status using management tooling and report endpoints that fail to apply scheduled updates

How to Mitigate CVE-2025-21408

Immediate Actions Required

Update Microsoft Edge to the latest stable channel release published on or after February 6, 2025
Verify automatic update functionality is enabled and not blocked by group policy or proxy configuration
Restrict execution of untrusted browser extensions and review currently installed add-ons
Reinforce user awareness regarding phishing links and unsolicited browser redirects

Patch Information

Microsoft addressed CVE-2025-21408 through a Microsoft Edge Stable Channel update. Administrators should consult the Microsoft CVE-2025-21408 Advisory for the exact fixed build number and apply it through Microsoft Update, WSUS, Intune, or other managed deployment channels. Restart Edge on every endpoint after deployment to load the patched binaries.

Workarounds

Use site isolation and SmartScreen filtering to reduce exposure to malicious pages
Block known malicious domains at the network perimeter and DNS layer until patching completes
Enforce least-privilege user accounts so successful exploitation yields limited host privileges

bash

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

# Force Edge update check via management command
"C:\Program Files (x86)\Microsoft\EdgeUpdate\MicrosoftEdgeUpdate.exe" /ua /installsource scheduler