Microsoft has published an advisory for CVE-2025-54906, a Microsoft Office vulnerability described as a “free of memory not on the heap” condition that can lead to local remote‑code‑execution (RCE) when a user opens or previews a specially crafted Office document; Microsoft lists the vulnerability in its Security Update Guide but the public advisory content is deliberately concise and, at the time of verification, the interactive MSRC page requires a JavaScript-enabled browser to render full details.
Microsoft Office vulnerabilities that allow code execution simply by opening or previewing documents remain one of the most consequential classes of flaws for enterprise defenders. Attackers weaponize Office documents because of Office’s ubiquity, the ease of mass distribution via email, and the long history of subtle memory-safety defects in Office’s parsers and legacy-format handlers. The general pattern—maliciously crafted document triggers a memory-corruption bug and the attacker gains execution in the user’s security context—has been repeatedly observed across 2024–2025 patch cycles. Independent vendor analyses of recent Patch Tuesday updates show multiple Office RCEs in the same timeframe and emphasize preview‑pane and parser bugs as high‑risk vectors. (cisa.gov)
The specific phrasing Microsoft uses—“free of memory not on the heap”—is unusual in plain English but meaningful to developers: it indicates that code invoked a free operation on a memory pointer that was not allocated from the expected heap allocator or that bookkeeping for dynamic allocations was mismatched. The result is undefined memory state that can be controlled or corrupted by an attacker who can craft input to manipulate downstream behavior. This class of defect often manifests as use‑after‑free, double‑free, or other memory-corruption scenarios that are exploitable for RCE in complex, multi-format parsers like Office’s. Several internal and third‑party writeups following Microsoft’s recent Office advisories explain the same exploitation patterns—malformed metadata/fields cause size miscalculations, freed memory is later referenced, or out‑of‑bounds reads/writes corrupt control structures—leading to arbitrary code execution.
Caveat: At the time of writing there was no widely published proof‑of‑concept exploit, and Microsoft did not report confirmed in‑the‑wild exploitation for this CVE in the public advisory text accessible without interactive rendering. That absence of public exploitation evidence should not be interpreted as low risk—document RCEs are high‑value to attackers and rapid weaponization following disclosure or patch publication is a common pattern. (msrc.microsoft.com, msrc.microsoft.com, msrc.microsoft.com, Security Update Guide - Microsoft Security Response Center
Background / Overview
Microsoft Office vulnerabilities that allow code execution simply by opening or previewing documents remain one of the most consequential classes of flaws for enterprise defenders. Attackers weaponize Office documents because of Office’s ubiquity, the ease of mass distribution via email, and the long history of subtle memory-safety defects in Office’s parsers and legacy-format handlers. The general pattern—maliciously crafted document triggers a memory-corruption bug and the attacker gains execution in the user’s security context—has been repeatedly observed across 2024–2025 patch cycles. Independent vendor analyses of recent Patch Tuesday updates show multiple Office RCEs in the same timeframe and emphasize preview‑pane and parser bugs as high‑risk vectors. (cisa.gov)The specific phrasing Microsoft uses—“free of memory not on the heap”—is unusual in plain English but meaningful to developers: it indicates that code invoked a free operation on a memory pointer that was not allocated from the expected heap allocator or that bookkeeping for dynamic allocations was mismatched. The result is undefined memory state that can be controlled or corrupted by an attacker who can craft input to manipulate downstream behavior. This class of defect often manifests as use‑after‑free, double‑free, or other memory-corruption scenarios that are exploitable for RCE in complex, multi-format parsers like Office’s. Several internal and third‑party writeups following Microsoft’s recent Office advisories explain the same exploitation patterns—malformed metadata/fields cause size miscalculations, freed memory is later referenced, or out‑of‑bounds reads/writes corrupt control structures—leading to arbitrary code execution.
What Microsoft says (and what we could verify)
Microsoft’s official listing for CVE-2025-54906 appears in the Microsoft Security Response Center (MSRC) vulnerability index. The MSRC entry name and the short description indicate a local code‑execution impact tied to an incorrect free operation for memory “not on the heap.” However, the MSRC web UI requires JavaScript for full rendering, which complicates automated scraping; the advisory’s canonical status remains intact but the vendor-published advisory content available to human readers is terse and omits low‑level exploit details. For administrators, the important actionable elements—affected product builds and KB update identifiers—are published in MSRC and via Microsoft’s normal update channels (Windows Update / Microsoft Update Catalog / Intune / WSUS). Cross‑checking vendor‑independent trackers and enterprise advisories is standard practice; as of the time this coverage was verified, major vulnerability trackers and enterprise bulletins show many Office memory‑corruption CVEs during 2025, but not every tracker had a fully indexed entry for CVE‑2025‑54906 when MSRC published the advisory. Where Microsoft publishes a new Office CVE, security vendors and CISA typically follow with summaries, CVSS scores, and mitigation guidance—however, indexing delays at databases like NVD and third‑party mirrors can occur. Administrators should therefore rely on Microsoft’s advisory and their own patch-management tooling for precise KB numbers rather than waiting for every third‑party index to update. (cisa.gov)Caveat: At the time of writing there was no widely published proof‑of‑concept exploit, and Microsoft did not report confirmed in‑the‑wild exploitation for this CVE in the public advisory text accessible without interactive rendering. That absence of public exploitation evidence should not be interpreted as low risk—document RCEs are high‑value to attackers and rapid weaponization following disclosure or patch publication is a common pattern. (msrc.microsoft.com, msrc.microsoft.com, msrc.microsoft.com, Security Update Guide - Microsoft Security Response Center
