Microsoft Edge CVE-2026-66315

Exploitation requires the target user to actively interact with attacker-controlled web content - such as navigating to a malicious URL, opening a crafted HTML file, or engaging with embedded content - while using Microsoft Edge (Chromium-based), satisfying the mandatory UI:R condition. The CVSS AC:H metric indicates the attacker must additionally achieve a specific memory layout or heap state in the Edge rendering process, likely involving a race condition or a controlled sequence of object allocations and deallocations; this is not a condition the attacker can reliably force on every visit, limiting opportunistic mass exploitation. PR:N confirms no authentication to the target system or browser is required from the attacker's perspective. The scope is unchanged (S:U), meaning impact is contained within the Edge browser process and does not inherently extend to OS-level privilege escalation. The primary factors limiting real-world exploitation are: mandatory user interaction, high attack complexity requiring precise memory manipulation, and the absence of any confirmed public exploit or POC at time of analysis.

The CVSS base score of 7.5 (High) is driven by full C/I/A impact but moderated by AC:H and UI:R. The temporal vector refines the picture further: Exploit Code Maturity E:U (Unproven) indicates no known functional exploit exists at time of scoring, and Remediation Level RL:O (Official Fix) confirms a vendor patch is available - both factors lower the operational urgency compared to a raw base-score reading. No CISA KEV listing is present, and no POC has been identified, meaning this is not a confirmed actively exploited vulnerability. AC:H implies the attacker must engineer specific heap or memory layout conditions - likely a race condition or controlled allocation sequence - which materially limits the pool of capable threat actors and reduces the likelihood of mass opportunistic exploitation. EPSS data was not provided in the source intelligence, preventing probabilistic exploitation-rate forecasting. Cross-referencing all signals: this is a genuine High-severity browser vulnerability warranting prompt patching for enterprise environments, but the AC:H, UI:R, and E:U combination means it does not represent an immediate emergency on par with KEV-listed or AC:L remote-execution flaws.

An attacker crafts a malicious web page engineered to trigger a specific memory allocation and deallocation sequence in Microsoft Edge's Chromium rendering engine, then distributes the URL via phishing, malvertising, or a compromised site. When the target user visits the page and interacts with the content - satisfying the UI:R requirement - the freed memory object is reclaimed and overwritten with attacker-controlled data, redirecting execution into arbitrary code running within the Edge browser process. The AC:H metric indicates reliable exploitation requires precise memory layout engineering, making opportunistic drive-by attacks less likely than targeted delivery; no public proof-of-concept code has been identified at time of analysis.