CVE-2023-21557
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 Lightweight Directory Access Protocol (LDAP) Denial of Service 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 confidenceThis is a Denial of Service (DoS) vulnerability in Windows Lightweight Directory Access Protocol (LDAP). The vulnerability allows an unauthenticated attacker to send specially crafted LDAP packets that can cause the LDAP service to become unresponsive or crash, disrupting authentication and directory services.
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 versionsall versionsall 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
- Network
- Complexity
- Low
- Privileges
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- None
- Integrity
- None
- Availability
- High
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
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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Identify Windows versionRun 'winver' or 'systeminfo | findstr /B /C:"OS Name" /C:"OS Version"' to determine the installed Windows version and build numberAffected if The version matches one of the affected releases: Windows 10 1607, 1809, 20h2, 21h2, 22h2; Windows 11 21h2, 22h2; or Windows 7 (all versions)
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Verify LDAP service is enabledCheck if the LDAP service is running by opening Services (services.msc) and looking for 'Active Directory Domain Services' or 'LDAP Service', or run 'Get-Service | Where-Object {$_.DisplayName -like "*LDAP*" -or $_.DisplayName -like "*Active Directory*"}' in PowerShellAffected if An LDAP-related service such as Active Directory Domain Services is installed and running on the system
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Confirm LDAP network listening portsRun 'netstat -an | findstr ":389 "' or 'netstat -an | findstr ":636 "' to check if LDAP ports 389 (LDAP) or 636 (LDAPS) are listening on network interfacesAffected if The system is listening on LDAP ports 389 or 636, indicating it is providing LDAP services over the network
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Assess network exposureReview firewall rules or network configuration to determine if LDAP ports are accessible from untrusted networks, using 'netsh advfirewall firewall show rule name=all' or by checking inbound firewall rules for port 389Affected if LDAP services are exposed to untrusted or external networks without proper network segmentation or filtering
A system is affected if it runs one of the vulnerable Windows versions listed, has an LDAP service enabled, and has that service reachable over the network where an attacker could send malicious LDAP packets.
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 Microsoft security update for CVE-2023-21557, which addresses the LDAP DoS vulnerability. Until patched, monitor LDAP service availability and implement network segmentation to limit exposure to untrusted networks.
- Consultation2.0 h
- Implementation4.0 h
- Testing3.0 h
- Review / QA2.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $3,088.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2023-21557 — 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-2023-21557 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