CVE-2026-56645: Heap-Based Buffer Overflow in Microsoft Edge – HIGH Severity RCE

Technical summary

A heap-based buffer overflow (CWE-122) exists in Microsoft Edge's Chromium engine. The vulnerability is reachable over the network and exploitable without authentication or special privileges. The attack vector requires user interaction, meaning a user must take an action (like clicking a link or opening content) to trigger the vulnerability. When successfully exploited, the attacker can corrupt heap memory and overwrite function pointers or other critical data structures, leading to arbitrary code execution within the browser process. The CVSS 3.1 score of 8.8 reflects high impact across confidentiality, integrity, and availability.

Business impact

Successful exploitation poses a significant threat to organizational confidentiality and system integrity. Users visiting compromised or malicious websites could have their systems compromised without further action by the attacker, enabling theft of credentials, session tokens, sensitive data stored in browser caches, or use of the system as a pivot point for lateral movement. For organizations with Edge as the standard browser, this creates a direct attack surface affecting potentially all end users. Incident response and remediation costs could be substantial, especially in enterprises with slow patch deployment cycles.

Affected systems

Microsoft Edge (Chromium-based) across all platforms is affected. This includes Windows, macOS, and Linux deployments of Chromium-based Edge. Organizations using Edge as a primary or mandated browser, as well as individual users, are in scope. The vulnerability does not affect Internet Explorer or non-Chromium browser engines, though any system running a vulnerable version of Edge is at risk.

Exploitability

The vulnerability is exploitable over the network but requires user interaction (UI:R in the CVSS vector), making it practically exploitable through social engineering, watering-hole attacks, or compromised legitimate websites. The attack complexity is low, meaning a standard exploit is likely feasible once developed. Given the high severity and straightforward attack mechanism, security researchers and threat actors have strong incentive to develop reliable exploits. However, as of the source data collection date, this vulnerability is not listed in the CISA Known Exploited Vulnerabilities (KEV) catalog, suggesting either no public active exploitation has been confirmed or the vulnerability is very recent.

Remediation

Remediation requires installing a patched version of Microsoft Edge released after the vulnerability publication date. Users and administrators should check Microsoft's official security advisory for the specific patch version addressing CVE-2026-56645. Apply the patch as soon as possible to all Edge instances in the environment, prioritizing user-facing systems and public-facing roles. For enterprises, consider using centralized deployment tools and Group Policy or Mobile Device Management (MDM) to enforce patch deployment. Verification testing should confirm that patched Edge versions function normally with critical business applications before broad rollout.

Patch guidance

Verify the latest Microsoft Edge version available through Microsoft's official security update channels and apply it immediately. Users running Windows can enable automatic updates for Edge or manually check Settings > About Microsoft Edge for available updates. Administrators managing enterprise deployments should consult Microsoft's official advisory (verify against the vendor advisory for specific patch version numbers) and deploy through their standard patch management processes. Test patches in a non-production environment first to confirm compatibility with internal web applications and extensions. Establish a timeline to reach 100% patch coverage within 30 days for systems with direct internet exposure.

Detection guidance

Monitor for suspicious Edge process behavior including unexpected child process creation, unusual network connections from browser processes, and file write operations to sensitive directories. Web proxy and endpoint detection and response (EDR) tools can flag attempts to access known malicious domains or exploit delivery sites. Web Application Firewalls (WAF) should be configured to detect payloads or request patterns associated with heap corruption attacks. Behavioral analytics can identify anomalies in Edge's memory access patterns post-exploitation. Additionally, track Edge version numbers across the environment and flag systems running versions published before the patch release date. Log authentication anomalies or lateral movement attempts originating from Edge user sessions on patched systems, as compromise during the vulnerability window may have left persistent access.

Why prioritize this

This vulnerability merits immediate priority due to its HIGH severity score (8.8), network-reachable attack vector, and low barrier to user-triggered exploitation. Heap-based buffer overflows in browser engines are high-confidence exploitation targets with potential for reliable remote code execution. The lack of KEV listing does not reduce urgency—it may indicate the vulnerability is very recent or that active exploitation has not yet been formally documented. Any browser vulnerability affecting code execution should be treated as a top-tier threat to endpoint security and corporate confidentiality.

Risk score, explained

The CVSS 3.1 score of 8.8 (HIGH) reflects the following: network accessibility (AV:N) means any internet-connected system is at risk; low attack complexity (AC:L) indicates a reliable exploit path; no authentication required (PR:N) means attackers need not be authorized users; user interaction is required (UI:R) but is easily satisfied through social engineering; no scope change (S:U) means the impact is limited to the affected component; and high impact across confidentiality (C:H), integrity (I:H), and availability (A:H) indicates potential for data theft, code execution, and denial of service. This score positions the vulnerability as a significant threat requiring urgent patching.

Frequently asked questions