CVE-2021-1699
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 · uneditedWindows (modem.sys) Information Disclosure Vulnerability
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 analysis · moderate confidenceAn information disclosure vulnerability exists in the Windows modem.sys driver. The vulnerability allows an attacker to potentially access sensitive information through the modem driver component. The CVSS 5.5 score indicates local access is required with low privileges to exploit this flaw.
Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.
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 versions= 20h2= 1607= 1803= 1809= 1909= 2004all versionsall versionsall versionsall versions= r2all versions= r2all versions= 20h2= 1909= 2004all 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
- Low
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- High
- Integrity
- None
- Availability
- None
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N
Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.
dbcve checksWork through these to decide whether this CVE applies to you.
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Check Windows versionRun 'winver' or 'systeminfo | findstr /B /C:"OS Name" /C:"OS Version"' to identify the installed Windows version and build numberAffected if The version matches any of the affected ranges: Windows 10 (all versions including 20h2, 1607, 1803, 1809, 1909, 2004), Windows 7 (all), Windows 8.1 (all), Windows RT 8.1 (all), Windows Server 2008 (all, R2), Windows Server 2012 (all, R2), Windows Server 2016 (all, 20h2, 1909, 2004), Windows Server
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Locate modem.sys driver fileCheck if the file C:\Windows\System32\modem.sys exists on the systemAffected if The file exists on the system - the vulnerability exists in this driver component
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Check modem.sys file versionRight-click C:\Windows\System32\modem.sys, select Properties, then view the File Version details, or run 'powershell (Get-Item C:\Windows\System32\modem.sys).VersionInfo'Affected if The driver is present and has not been patched - compare against Microsoft's patch date for CVE-2021-1699 (February 2021 security updates)
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Verify modem diagnostics feature statusOpen Settings > Network & Internet > Status > Network reset, or check Device Manager under Modems to see if any modem devices are present or enabledAffected if A modem device or the modem diagnostics feature is enabled or has been used on the system, increasing the attack surface for this vulnerability
The system is likely affected if it runs any Windows version from the affected list and contains the modem.sys driver, especially if the February 2021 security updates have not been installed.
Generated from the published advisory. Verify against your own configuration.
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 dataApply the relevant Microsoft security updates for Windows that address the modem.sys vulnerability. Verify that affected systems receive the patch through standard Windows Update or enterprise patch management deployment.
- Consultation2.0 h
- Implementation4.0 h
- Testing3.0 h
- Review / QA1.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $2,800.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2021-1699 — 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 sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2021-1699 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
No notes yet
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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