CVE-2026-70310 Overview
CVE-2026-70310 is an out-of-bounds read vulnerability [CWE-125] in Microsoft Office Word. An unauthorized attacker can exploit the flaw to disclose sensitive information locally. The vulnerability requires user interaction, typically opening a crafted Word document. Microsoft has published guidance through the Microsoft Security Response Center (MSRC).
The issue does not enable code execution or data modification directly. However, leaked memory contents can include process data useful for chaining with other vulnerabilities. The CVE was published to the National Vulnerability Database (NVD) on 2026-08-11.
Critical Impact
Successful exploitation exposes in-process memory contents from Microsoft Word, potentially revealing sensitive document data, address layout information, or other artifacts useful in follow-on attacks.
Affected Products
- Microsoft Office Word (see the Microsoft Security Update CVE-2026-70310 advisory for specific build ranges)
Discovery Timeline
- 2026-08-11 - CVE-2026-70310 published to NVD
- 2026-08-11 - Last updated in NVD database
Technical Details for CVE-2026-70310
Vulnerability Analysis
The vulnerability is an out-of-bounds read [CWE-125] in Microsoft Office Word's document parsing logic. When Word processes a specially crafted file, it reads memory beyond the bounds of an intended buffer. The excess data is then incorporated into program state accessible to the attacker's document context, resulting in information disclosure.
Exploitation requires the victim to open a malicious document on the local system. The attacker does not need prior authentication to the target machine. Impact is limited to confidentiality; integrity and availability are not affected according to the CVSS vector provided by Microsoft.
Because the flaw discloses memory rather than executing code, it is commonly used as a primitive in larger attack chains. Adversaries may combine leaked pointers or heap contents with a separate memory-corruption bug to defeat mitigations such as Address Space Layout Randomization (ASLR).
Root Cause
Out-of-bounds read conditions in Office parsers typically stem from missing or incorrect length validation of record fields within compound document structures. When the parser trusts an attacker-controlled size or offset without bounding it against the actual buffer, it reads beyond the allocation. Refer to the Microsoft Security Update CVE-2026-70310 advisory for authoritative root-cause guidance.
Attack Vector
The attack vector is local and requires user interaction. A user must open a crafted Word document delivered through email, chat, a network share, or a web download. Once opened, Word processes the malformed structure and leaks memory to attacker-controlled fields within the document or to embedded scripting. Verified public proof-of-concept code is not currently available for this CVE.
Detection Methods for CVE-2026-70310
Indicators of Compromise
- Unexpected Word process crashes or abnormal termination events (WINWORD.EXE) shortly after opening a document from an untrusted source.
- Word documents originating from external senders that contain unusually large or malformed OLE/OOXML structures.
- Outbound network connections initiated by WINWORD.EXE shortly after document open, potentially exfiltrating leaked content.
Detection Strategies
- Inspect inbound .doc, .docx, .rtf, and related attachments at the email gateway using content disarm and reconstruction (CDR) or sandbox detonation.
- Alert on WINWORD.EXE spawning script interpreters (wscript.exe, powershell.exe, cmd.exe) or making unusual outbound connections.
- Correlate Office telemetry with endpoint process events to identify document-driven anomalies across users.
Monitoring Recommendations
- Enable Microsoft Office cloud protection and attack surface reduction (ASR) rules that block Office child-process creation.
- Forward Office and endpoint logs to a centralized analytics platform for cross-user correlation of suspicious document activity.
- Track patch compliance for Microsoft Office across the fleet and alert on unpatched hosts opening external documents.
How to Mitigate CVE-2026-70310
Immediate Actions Required
- Apply the Microsoft security update referenced in the Microsoft Security Update CVE-2026-70310 advisory to all affected Office installations.
- Prioritize patching for users who routinely process external documents, including executives, HR, finance, and legal staff.
- Verify that Protected View and Office macro-blocking policies are enforced through Group Policy or Intune.
Patch Information
Microsoft has released updates through its standard servicing channels. Consult the Microsoft Security Update CVE-2026-70310 advisory for the specific KB articles, click-to-run builds, and MSI packages applicable to your deployment.
Workarounds
- Open untrusted documents in Protected View or the Office viewer sandbox until patches are deployed.
- Block or quarantine Office documents from external senders at the mail gateway when business workflows allow.
- Restrict document delivery channels by disabling automatic preview in mail clients and file explorers.
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
