Microsoft's advisory confirms a use‑after‑free flaw in Microsoft Excel that can lead to local code execution when a specially crafted spreadsheet is opened, creating a potentially serious escalation path on unpatched systems.
This vulnerability, tracked as CVE‑2025‑54904, is listed in Microsoft's Security Update Guide with the short description that a use‑after‑free in Microsoft Office Excel allows an unauthorized attacker to execute code locally. Microsoft’s advisory page lists the entry but renders via JavaScript (the page requires a browser to display full metadata), and at the time of writing Microsoft’s online summary is the authoritative vendor statement available.
Independent vulnerability aggregators also show CVE‑2025‑54904 in their feeds and track it as a newly published Excel memory‑corruption issue, but at the moment public feeds indicate that CVSS scoring and exploit metrics were not immediately available in the public databases. This means analysts must rely on the vendor advisory and standard mitigation practices until scoring and exploitability data are formalized in NVD or other scoring authorities.
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Source: MSRC Security Update Guide - Microsoft Security Response Center
Overview
This vulnerability, tracked as CVE‑2025‑54904, is listed in Microsoft's Security Update Guide with the short description that a use‑after‑free in Microsoft Office Excel allows an unauthorized attacker to execute code locally. Microsoft’s advisory page lists the entry but renders via JavaScript (the page requires a browser to display full metadata), and at the time of writing Microsoft’s online summary is the authoritative vendor statement available. Independent vulnerability aggregators also show CVE‑2025‑54904 in their feeds and track it as a newly published Excel memory‑corruption issue, but at the moment public feeds indicate that CVSS scoring and exploit metrics were not immediately available in the public databases. This means analysts must rely on the vendor advisory and standard mitigation practices until scoring and exploitability data are formalized in NVD or other scoring authorities.
Background: use‑after‑free in Office is a recurring class of risk
Memory‑corruption flaws like use‑after‑free and buffer overflow have long been a frequent source of remote and local code execution vulnerabilities in Microsoft Office components. Throughout 2025 Microsoft published multiple separate Excel advisories describing memory‑management defects that could be abused to run arbitrary code when an attacker gets a target to open a crafted file. These advisories follow a consistent pattern: improperly managed object lifetimes in Excel’s parsing or rendering code create references to freed memory, and an attacker crafts input that forces execution down that path. Seeing one more Excel use‑after‑free should be read as part of that broader pattern rather than an isolated engineering anomaly. (feedly.com, cvedetails.com)- Past 2025 advisories show Excel vulnerabilities with similar descriptions and, in many cases, CVSS vectors assigned as local with user interaction required, reflecting the typical exploitation model for malicious Office documents.
- Microsoft maintains individual advisory pages for each CVE entry in the Security Update Guide; those pages are the primary source for the exact list of affected products and for Microsoft’s recommended updates.
What Microsoft says (vendor summary)
Microsoft’s entry for CVE‑2025‑54904 states that the issue is a use‑after‑free in Excel that allows an unauthorized attacker to execute code locally. The wording indicates:- The underlying root cause is memory management (use‑after‑free).
- The impact is local arbitrary code execution (attacker gains ability to run code under the privileges of the user who opens the file).
- Microsoft’s advisory entry is the canonical description; for details on affected versions, build numbers, or patch KBs, Microsoft’s Security Update Guide page for the CVE is the authoritative source but requires viewing the dynamic page to enumerate product‑specific fix information.
Technical analysis — how a use‑after‑free becomes code execution
What is a use‑after‑free?
A use‑after‑free (UAF) condition happens when a program frees (releases) memory but later continues to use a pointer that refers to that freed memory. An attacker who can control the data or the timing around allocation/free operations can often arrange for the freed memory to be reallocated with attacker‑controlled content, leading to memory corruption, crash, or even execution of attacker‑controlled code.Why Excel is a target
Excel processes complex, feature‑rich file formats: formulas, embedded objects, charts, ActiveX controls, OLE objects, fonts, and rendering paths. These increase attack surface and complexity in memory management. Parsing, rendering, or object lifecycle logic that fails to maintain correct ownership semantics or to sanitise malformed input can create UAF windows. Historical advisories in 2025 demonstrate multiple distinct UAF and buffer overflow defects across Excel builds. (cvedetails.com, feedly.com)Likely exploitation model for CVE‑2025‑54904
Microsoft’s one‑line description (“execute code locally”) strongly implies this variant requires that a user open a malicious spreadsheet on the target machine (or the file be rendered by an Office server component that opens files on a user’s behalf). In practical terms the exploitation chain typically looks like:- Attacker crafts a malicious .xlsx/.xlsb/.xls file that triggers the use‑after‑free during parsing or rendering.
- Victim opens the file in Excel (user interaction).
- Freed memory gets reused with attacker‑controlled content; the control flow is hijacked to run payload code in the context of the victim (local code execution).
- Effects can range from an arbitrary program running to payloads that establish persistence depending on the victim’s privileges.
Affected products and severity: what we can and cannot verify
- Microsoft’s Security Update Guide lists the CVE entry; however, the dynamic page requires the vendor’s UI to enumerate the specific affected Office builds and patch KB numbers. The advisory title and description are verified by Microsoft’s advisory page. Because the rendered page content can vary and is JavaScript‑driven, readers are advised to consult Microsoft’s update portal directly for their environment’s exact affected build list and remediation KB.
- Third‑party aggregators that track CVEs show CVE‑2025‑54904 appearing in feeds (Feedly and similar) with a publication date in early August 2025, but some aggregators indicate No CVSS yet, which confirms that scoring authorities had not posted a formal CVSS metric at the time those feeds captured the entry. This lack of immediate CVSS scoring is not unusual — vendor advisories are often published before NVD or other databases finalize scores. Analysts should treat the absence of a CVSS score as a sign to prioritize patching on the basis of vendor severity and exploitation context rather than waiting for a numeric score.
- For context, many Excel UAF CVEs from 2025 received CVSS v3.1 vectors in the 7.8 range when scored — typically due to local attack vector combined with high integrity/confidentiality impact. While CVE‑2025‑54904’s exact score must be confirmed, it is reasonable to consider it in the same risk band until a formal score is posted. This is an analytical inference based on the class of vulnerability and past advisory patterns and should be treated with caution until an authoritative score is available. (feedly.com, app.opencve.io)
Immediate risk assessment
- Attack complexity: likely low for exploit developers who already have deep knowledge of Office internals, but practical exploitation depends on being able to get targets to open the malicious file (user interaction). Many Excel memory corruption bugs historically required only standard social engineering.
- Scope of impact: local code execution under the context of the user. If the user runs with administrative privileges, the impact is far greater. Typical enterprise mitigations (least privilege, application control) significantly reduce blast radius.
- Exploit availability: as of the advisory’s initial appearance, public proof‑of‑concepts were not widely reported in major exploit repositories; however, historically once a vulnerability like this is published unpatched, proof‑of‑concepts often appear within days to weeks. Organizations should assume a risk window and patch quickly.
Mitigation and prioritized action plan
The priority for system administrators and users is to eliminate the exposure by applying Microsoft’s official updates. Because Microsoft’s advisory lists the CVE in the Security Update Guide, the vendor has released (or will release) fixes that correspond to specific Office versions and build numbers. Follow these steps in sequence:- Immediately identify Excel/Office versions in your environment and map them to Microsoft’s advisory to find the exact KB or update that addresses CVE‑2025‑54904. Consult the vendor advisory for build‑level mappings.
- Prioritize patch deployment for high‑risk endpoints: users with elevated privileges, machines in sensitive networks, and systems that handle untrusted documents. Use standard change control but accelerate the rollout for vulnerable classes.
- Where immediate patching is not possible, apply compensating controls:
- Enable Excel’s Protected View for files originating from the internet and from potentially untrusted locations.
- Block or heavily filter incoming attachments of Excel workbook types at the email gateway where possible.
- Use application allow‑listing (AppLocker, Windows Defender Application Control) to prevent arbitrary binaries from running even if a memory corruption is exploited.
- Ensure users run with least privilege (standard user accounts) instead of local administrator.
- Monitor telemetry: enable/inspect endpoint detection and response (EDR) logs for suspicious child processes spawned from Excel, anomalous code injection indicators, or persistence artifacts. Increase logging on systems that cannot be patched immediately.
- Educate users: remind staff about the risks of opening unsolicited or unexpected spreadsheets, especially those with macros or embedded content. Prefer secure file sharing channels and verify senders out of band.
- For server‑side exposures (Office Online Server, file‑rendering services), isolate and prioritize these systems — they can be leveraged for remote exploitation if the server renders untrusted files for clients. Confirm vendor guidance for server updates. (feedly.com, msrc.microsoft.com)
Longer‑term controls to reduce future memory‑corruption risk
- Enforce the principle of least privilege across endpoints and service accounts. Memory‑corruption exploits that succeed under a non‑privileged user are significantly less catastrophic.
- Use modern application control and sandboxing where possible to isolate Office processes from critical system components.
- Move sensitive document processing to hardened, patched services with strong content sanitization, and limit direct user access to raw attachments in high‑risk sectors.
- Invest in proactive testing: fuzzing and memory‑safety testing of document parsers has repeatedly found these classes of bugs before attackers do; coordinate vulnerability disclosure with vendors where issues are discovered.
- Adopt an incident playbook for in‑the‑wild Office exploits: triage, isolate, patch, hunt for indicators of compromise, and restore from known‑good backups if necessary.
Why organizations should act now — and what to watch for
Microsoft’s advisory confirms the vulnerability exists; external feeds have indexed the CVE ID and flagged it as a memory‑corruption Excel issue with potential local RCE. Given the track record of Office exploits appearing in the wild after advisories are published, delaying mitigations increases the window of exposure. The immediate priority is patching plus short‑term compensating controls for systems that cannot be updated at once. (msrc.microsoft.com, feedly.com)Watch for:
- Microsoft publishing the exact affected build list and KB update IDs on the Security Update Guide page for CVE‑2025‑54904.
- NVD, CISA, or other national vulnerability databases assigning a CVSS score and adding detailed technical metadata. When those scores appear, they will help refine prioritization.
- Proof‑of‑concept exploits or active exploitation reports — these often migrate quickly into exploit feeds after an advisory is public.
Strengths and limitations of current public information
Strengths
- The vendor has assigned a canonical CVE and published an advisory entry, which is the most important step for coordinated remediation. Microsoft’s Security Update Guide is the authoritative location to find which builds are affected and which patches to apply.
- Third‑party aggregators and vulnerability feeds have already indexed the CVE, raising awareness across security teams and automated scanners.
Limitations and risks
- As of initial posting, public scoring and exploitability metadata were not yet universally published by NVD or other central databases; this is a common timing gap but it complicates automated prioritization workflows that rely solely on CVSS numbers. Analysts must therefore act on vendor guidance and risk context rather than waiting for numeric scores.
- The Security Update Guide page uses dynamic content; automated scanners that do not execute JavaScript may miss the full product/patch mapping. Human review of the Microsoft advisory is recommended to confirm the affected versions and KBs.
- Public exploit code was not reported in mainstream exploit repositories at the initial appearance; however, absence of proof‑of‑concept is not evidence of safety. Historically, once the vulnerability is public and unpatched, proof‑of‑concepts follow.
Conclusion
CVE‑2025‑54904 is another entry in a continuing series of Microsoft Excel memory‑corruption advisories in 2025. Microsoft’s advisory confirms a use‑after‑free condition in Excel that can lead to local code execution; third‑party feeds have captured the CVE but public scoring was not immediately available. The practical response for IT teams is straightforward: consult Microsoft’s Security Update Guide for the exact update that patches CVE‑2025‑54904, deploy the update across affected endpoints as a priority, and apply compensating controls where immediate patching is infeasible. Treat this advisory as high‑priority for remediation planning and hunting, and do not delay applying vendor fixes. (msrc.microsoft.com, feedly.com)Source: MSRC Security Update Guide - Microsoft Security Response Center
