CVE-2025-54910: Office Heap Overflow Leading to Local Code Execution — Patch Guidance

Microsoft’s Security Update Guide lists CVE-2025-54910 as a heap-based buffer overflow in Microsoft Office that can allow an attacker to execute code locally when a crafted Office document is processed, but the vendor’s advisory requires direct inspection for exact builds and KB identifiers because the MSRC page content is rendered client‑side. (msrc.microsoft.com)

Background​

Microsoft Office continues to be a primary target for memory‑corruption vulnerabilities because of its ubiquity and the complexity of the file formats it supports. Heap‑based buffer overflows in Office parsers — whether in Word, Excel, PowerPoint, Visio, or ancillary components — typically arise when a parser allocates a heap buffer and then writes more data than the buffer can hold. The result can be corrupted heap metadata, overwritten function pointers or vtable entries, and ultimately control‑flow hijack that leads to arbitrary code execution in the context of the process that opened the file. (nvd.nist.gov)
Microsoft’s Security Update Guide is the canonical source for CVE → KB → affected product mappings; however, the MSRC web UI uses JavaScript to render the full advisory content, which complicates automated scraping and sometimes delays third‑party aggregators from indexing the advisory text and KB IDs. For defenders this means: treat MSRC as authoritative, and verify affected builds and KB numbers in your patch management system (WSUS/SCCM/MECM, Intune, Microsoft Update Catalog) rather than relying solely on third‑party mirrors. (msrc.microsoft.com)

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What the vulnerability is (technical overview)​

The class: heap‑based buffer overflow​

A heap‑based buffer overflow occurs when code allocates a buffer on the heap and subsequently writes more bytes into it than were allocated. In Office document parsers this typically stems from:

• Malformed length or size fields in embedded objects (images, OLE streams, shape metadata).
• Integer arithmetic errors (wraps/overflows) that produce smaller-than-intended allocation sizes.
• Incomplete bounds checks during decompression, copy, or concatenation operations.

When adjacent heap metadata or object structures are overwritten, an attacker who can influence the overwritten bytes may be able to modify pointers or control‑data and later redirect execution to attacker‑controlled memory. Real‑world exploitation chains generally combine the memory primitive with techniques to bypass DEP/NX and ASLR (ROP chains, JIT‑spraying, information leaks, heap grooming).

Attack vector and prerequisites​

The vendor description for CVE-2025-54910 lists the impact as code execution in the context of the user who opens the file. Historically this family of Office bugs is delivered via:

• Email attachments (phishing), drive‑by downloads, cloud‑share file links.
• Shared collaboration spaces and file servers where users open or preview documents.
• In some prior cases preview panes (Outlook / Explorer) have allowed “no explicit open” exploitation; whether preview is relevant to CVE‑2025‑54910 should be confirmed in Microsoft’s advisory before concluding it applies in your environment.

Exploitation generally requires user interaction (opening or previewing a crafted document), meaning the CVE’s “remote code execution” label describes the attacker’s ability to send the malicious file from a remote location — the actual exploit still needs the victim to process the file locally. That reduces but does not eliminate operational risk: document‑based RCEs are frequently used as initial access vectors that are chained with follow‑on behavior (credential theft, lateral movement, ransomware deployment).

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What is known and what remains unverified​

• Known: MSRC lists CVE‑2025‑54910 as a heap‑based buffer overflow in Microsoft Office that can lead to code execution in the user context. The MSRC entry is the authoritative vendor statement and should guide remediation. (msrc.microsoft.com)
• Verified pattern: Similar Office heap overflows patched earlier in 2025 have affected multiple Office servicing channels (Microsoft 365 Apps / Click‑to‑Run, Office LTSC/perpetual releases, Office Online Server), so expect Microsoft to provide updates across channels where applicable.
• Unverified / caution: At the time of writing, independent public trackers and aggregators may not have fully populated entries for CVE‑2025‑54910 (indexing lag is common when MSRC content requires client‑side rendering). That means third‑party CVSS scores, per‑product CPEs, or KB numbers may not be available everywhere; rely on MSRC and your patch management tooling for exact package names and KB IDs. Treat any numeric scores or “exploited in the wild” claims from secondary sources as provisional until corroborated by Microsoft, CISA, or major vendors.

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Practical risk assessment​

A heap‑based overflow in Office remains a high‑impact finding for most environments:

• Immediate endpoint compromise under user privileges is the typical first step; that may include credential theft, lateral movement, staging for privilege escalation, or ransomware deployment.
• Blast radius depends on user privileges. If targeted users have admin rights, the risk of full system compromise and persistence is significantly higher.
• Exploitability: Document‑open vectors require social engineering, but attackers routinely weaponize such bugs quickly after disclosure or patch publication — especially when PoCs are released or patches expose fix details.

Organizations with aggressive patch windows or strong email and endpoint defenses will reduce exposure, but because Office is widely used the potential for rapid, mass exploitation is real — treat this as a high‑priority remediation candidate until your specific telemetry demonstrates otherwise.

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Immediate actions (operational checklist)​

Apply a risk‑based, measurable response now. The list below is ordered from highest to lower priority.

• Patch first
• Retrieve the MSRC advisory entry for CVE‑2025‑54910 and extract the KB numbers for each affected Office SKU and servicing channel from Microsoft’s Security Update Guide or your update catalog. Apply the vendor‑supplied updates as the first and definitive mitigation. (msrc.microsoft.com)
• If you cannot patch immediately — apply containment
• Enforce Protected View for files from the internet and Outlook attachments.
• Disable Office preview/thumbnail rendering in high‑risk mailboxes and on servers that ingest untrusted documents.
• Block Office applications from creating child processes (enable relevant Attack Surface Reduction (ASR) rules in Microsoft Defender / Defender for Endpoint); deploy in audit mode first and then move to block after tuning.
• Hardening and prevention
• Apply Application Guard for Office where available (isolates document rendering in a containerized environment).
• Enforce least privilege: remove unnecessary local admin rights that increase exploitation impact.
• Harden mail gateways and use sandbox detonation for attachments from untrusted senders.
• Detection and hunting
• Monitor EDR/NGAV telemetry for Office processes spawning suspicious children (WINWORD.EXE, EXCEL.EXE, VISIO.EXE → PowerShell/cmd/wscript/rundll32). Use your EDR’s advanced hunting queries or Defender Advanced Hunting (DeviceProcessEvents) to build alerts.
• Hunt for new persistence artifacts or unusual network callbacks shortly after Office process events.
• Communication and change control
• Test the patch on a pilot group, confirm business‑critical macros and add‑ins remain functional, then schedule an expedited rollout with documented rollback plans.
• Notify helpdesk and IR teams to expect possible post‑exploit alerts and to follow a prepared incident playbook for Office‑related compromises.

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Detection guidance — concrete examples​

• High‑value indicators:
• Office process creation of child processes: WINWORD.EXE/EXCEL.EXE/VISIO.EXE spawning cmd.exe, powershell.exe, wscript.exe, or rundll32.exe.
• Rapid, repeated crashes in Office modules or anomalous Office process memory allocations.
• Network connections initiated immediately after Office file open events to IPs/domains not seen in baseline telemetry.
• Example Defender Advanced Hunting (conceptual) query:
• DeviceProcessEvents | where FileName in ("winword.exe","excel.exe","visio.exe") | where ProcessCommandLine contains_cs "powershell" or ProcessCommandLine contains_cs "cmd.exe" | project Timestamp, DeviceName, FileName, ProcessCommandLine, InitiatingProcessFileName. Adapt to your telemetry schema and tune for false positives.

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Recommended patch management workflow​

• Inventory
• Use WSUS/SCCM/MECM or Intune to enumerate Office builds across channels (Monthly Enterprise Channel, Semi‑Annual Channel, LTSC, Click‑to‑Run).
• Map MSRC’s affected SKUs / KB numbers to your inventory and prioritize hosts with high business impact or elevated privileges.
• Test
• Validate the update on representative endpoints, including those with common add‑ins (line‑of‑business macros, third‑party Office integrations).
• Deploy
• Stage rollout: pilot → broad enterprise.
• For unmanaged devices, publish user guidance and require installation via Microsoft Update or Office Update.
• Verify
• Confirm build numbers or installed KB revisions via your management console, reporting and tagging endpoints as remediated.

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Exploitation and post‑exploit scenarios (threat modeling)​

• Typical attacker flow:
• Phishing email with a weaponized Office document (or targeted drop in a cloud share).
• Victim opens or previews the document; parsing triggers the heap overflow and results in RCE under the user context.
• Attacker runs a loader or reconnaissance commands; if user is privileged or additional EoP bugs are chained, privilege escalation may follow.
• Lateral movement, credential harvesting, persistence (scheduled tasks, services), and data exfiltration or ransomware deployment.
• Why attackers prize Office heap overflows:
• They sometimes don’t require macros or scripting.
• They can be weaponized in targeted and commodity campaigns.
• Office’s reach across enterprise endpoints creates a large attack surface for mass distribution.

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Strengths and limitations of vendor guidance​

• Strengths:
• Microsoft’s Security Update Guide is authoritative for the precise mapping of CVEs to KBs and affected builds, which is necessary for targeted remediation. (msrc.microsoft.com)
• Vendor advisories often include short‑term mitigations and recommended operator actions (e.g., protected view, ASR rules).
• Limitations / operational cautions:
• The MSRC UI’s client‑side rendering can delay automated indexing; third‑party trackers may lag in listing CVSS scores, KB IDs, or exploitation notes. Always confirm KB numbers in your patch tooling.
• Some hardening steps (disabling preview panes, enforcing ASR rules, disabling macros) can disrupt legitimate workflows; test changes before enforcing at scale.

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Governance checklist for IT leaders​

• Confirm whether your estate includes any of Microsoft’s affected Office builds for CVE‑2025‑54910; use MSRC and your patch management telemetry to extract KB IDs and build numbers. (msrc.microsoft.com)
• Prioritize patches for:
• Admins, privileged users, and machines that access sensitive data.
• Externally facing systems or mail‑facing inboxes that handle untrusted documents.
• Ensure compensating controls are in place while patching:
• Mail sandboxing and detonation.
• ASR rule enforcement tuned to avoid operational friction.
• Endpoint backups and recovery plans in case of post‑exploit impact.
• Document rollouts, exceptions, and acceptance criteria for re‑enabling any temporarily disabled features.

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Final analysis and risk posture​

CVE‑2025‑54910 fits a recurring and dangerous pattern: Office document parsers with memory‑safety bugs that lead to local code execution. Although exploitation typically requires user interaction, these bugs have high real‑world value for attackers and are frequently incorporated into phishing and targeted campaigns. Microsoft’s Security Update Guide entry is the definitive remediation source; defenders must immediately map the vendor’s KBs to their estate and patch following validated change control procedures. If you cannot patch every endpoint immediately, apply layered mitigations — Protected View, Application Guard, ASR rules, mail sandboxing, and EDR detection — while you stage updates.
Caveat: exact per‑product KB identifiers, CVSS scoring, and in‑the‑wild exploitation status for CVE‑2025‑54910 were not consistently indexed across the public aggregators consulted during this review; consult Microsoft’s advisory and your internal patching systems to extract authoritative KB numbers and confirm patch availability before executing large scale rollouts. (msrc.microsoft.com)

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CVE‑2025‑54910 is a critical reminder that even well‑maintained productivity suites remain high‑value attack vectors. Practical, measurable steps — timely patching, layered mitigations, and focused telemetry hunts — will materially reduce risk while organizations verify and deploy the vendor fixes.

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Source: MSRC Security Update Guide - Microsoft Security Response Center