This CVE is a local out-of-bounds read in Microsoft Office's document parsing layer. The attack vector is straightforward: a victim opens a crafted file, and Office reads memory outside the document buffer, exposing data that should have been inaccessible. No code execution is required—just file open. That matters because it lowers the attacker门槛 significantly. They don't need phishing with credential theft; they need one document opened. The CVSS 5.5 is technically accurate for the disclosure event itself, but it misrepresents the actual risk. An OOB read in the parsing path isn't the terminal impact—it reconnoiters. If this occurs before heap hardening, ASLR entropy establishment, or credential clearing activates (all of which happen at different points in Office's startup sequence), it can fingerprint memory layout, expose loaded DLL versions, or surface fragments of previously-processed data. This transforms the vulnerability from an information disclosure into a reconnaissance enabler for subsequent, higher-severity attacks. Treat the CVSS score as a floor, not a ceiling. The more important question isn't the severity number—it's why this class of bug persists. Microsoft has been patching OOB reads in Office parsers for over two decades. If each instance were an isolated procedural miss, decades of SDL investment should have eliminated this pattern. The fact that it keeps reproducing suggests the parsing architecture creates structural pressure points: complex state, performance-sensitive code paths, and document content influencing pointer arithmetic in ways that make bounds handling perpetually error-prone. What to do: patch immediately. But also treat this as a signal to audit your Office exposure. If you process untrusted documents at scale—particularly in high-value target environments—consider whether those documents are being opened in isolated sandboxed processes before user authentication, or whether the parsing occurs in the main Office session where credential handling and memory state are more exposed. The difference in blast radius is substantial.
CVE-2026-64899
Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.
NVD · uneditedOut-of-bounds read in Microsoft Office allows an unauthorized attacker to disclose information locally.
In the news
Third-party coverageSurfaced from public web coverage — external links open in a new tab.
Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.
dbcve analysisThe code reads past the end (or before the start) of a buffer, returning memory that was never meant to be exposed. Attackers use it to leak secrets like keys or to defeat memory-protection defences. Remediation is validating indices and lengths before every read.
General guidance for the out-of-bounds read class — the official description and references above are authoritative for this specific CVE. Want a bespoke review and a reviewed fix? Ask our team →
Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.
NVD · CPE dataall versionsall versionsall versionsall versionsall versionsall versionsCVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.
From the vector- Attack vector
- Local
- Complexity
- Low
- Privileges
- None
- User interaction
- Required
- Scope
- Unchanged
- Confidentiality
- High
- Integrity
- None
- Availability
- None
CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:N/A:N
Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.
From vendor dataThere is no version to upgrade to and no patch to apply. Every affected install stays exposed until the vendor ships a fix — or somebody else builds one.
Free. We build fixes in the order the community asks for them — and we’ll tell you the moment this one lands.
We develop and verify an original fix where the vendor hasn’t, from $7,100. Deployed to your staging first — never straight to production.
Scope it with usSee what else the community needs solved on the solutions-needed board.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2026-64899 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesThis CVE is a local out-of-bounds read in Microsoft Office's document parsing layer. The attack vector is straightforward: a victim opens a crafted file, and Office reads memory outside the document buffer, exposing data that should have been inaccessible. No code execution is required—just file open. That matters because it lowers the attacker门槛 significantly. They don't need phishing with credential theft; they need one document opened. The CVSS 5.5 is technically accurate for the disclosure event itself, but it misrepresents the actual risk. An OOB read in the parsing path isn't the terminal impact—it reconnoiters. If this occurs before heap hardening, ASLR entropy establishment, or credential clearing activates (all of which happen at different points in Office's startup sequence), it can fingerprint memory layout, expose loaded DLL versions, or surface fragments of previously-processed data. This transforms the vulnerability from an information disclosure into a reconnaissance enabler for subsequent, higher-severity attacks. Treat the CVSS score as a floor, not a ceiling. The more important question isn't the severity number—it's why this class of bug persists. Microsoft has been patching OOB reads in Office parsers for over two decades. If each instance were an isolated procedural miss, decades of SDL investment should have eliminated this pattern. The fact that it keeps reproducing suggests the parsing architecture creates structural pressure points: complex state, performance-sensitive code paths, and document content influencing pointer arithmetic in ways that make bounds handling perpetually error-prone. What to do: patch immediately. But also treat this as a signal to audit your Office exposure. If you process untrusted documents at scale—particularly in high-value target environments—consider whether those documents are being opened in isolated sandboxed processes before user authentication, or whether the parsing occurs in the main Office session where credential handling and memory state are more exposed. The difference in blast radius is substantial.
Practitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2026-64899 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.
- Verified mitigations, workarounds, and config changes
- Version or environment caveats, and links to real fixes
- No weaponised exploit code, or anything meant to cause harm
- No spam, self-promotion, credentials, or personal data