CVE-2001-1533
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 · uneditedMicrosoft Internet Security and Acceleration (ISA) Server 2000 allows remote attackers to cause a denial of service via a flood of fragmented UDP packets. NOTE: the vendor disputes this issue, saying that it requires high bandwidth to exploit, and the server does not experience any instability. Therefore this "laws of physics" issue might not be included in CVE
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 confidenceMicrosoft ISA Server 2000 is vulnerable to denial of service via fragmented UDP packet floods. Remote attackers can send large numbers of fragmented UDP packets to exhaust server resources and disrupt service.
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 data= 2000CVSS 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
- Low
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
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.
-
Confirm ISA Server 2000 installationCheck for ISA Server 2000 in Add/Remove Programs, or check the registry key HKLM\SOFTWARE\Microsoft\ISA Server\CurrentVersion for a value indicating version 2000, or look for the ISA Server service running on the system.Affected if ISA Server 2000 is installed and running on the system.
-
Verify network exposure to untrusted UDP trafficDetermine if the ISA Server interface is directly exposed to the internet or an untrusted network by reviewing network adapter bindings and firewall rules. Check if UDP port 500 or other UDP services are listening on external interfaces.Affected if ISA Server 2000 has a public-facing network interface that accepts UDP traffic from untrusted sources.
-
Inspect ISA Server logs for fragmented UDP patternsReview ISA Server monitoring logs (typically in C:\ISA\ISALogs\ or via the ISA Management console) for unusually high volumes of fragmented UDP packets, dropped packets, or service degradation events around the time of suspected attacks.Affected if Logs show excessive fragmented UDP packet processing or resource exhaustion events.
-
Check Windows Event Viewer for DoS indicatorsOpen Windows Event Viewer and look under System and Security logs for event IDs related to network buffer exhaustion, UDP packet floods, or ISA Server service instability.Affected if Event logs contain entries indicating UDP-related resource exhaustion or ISA Server service failures.
The environment is affected if Microsoft ISA Server 2000 is installed and exposed to untrusted UDP traffic, as the vulnerability allows remote attackers to exhaust server resources via fragmented UDP packet floods.
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 dataImplement network-level filtering to block or rate-limit malformed/fragmented UDP packets at the perimeter. Configure IDS/IPS rules to detect and mitigate UDP flood attacks. Consider upgrading from ISA Server 2000 as it is legacy software.
- Consultation2.0 h
- Implementation3.0 h
- Testing2.0 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 $2,272.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2001-1533 — 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-2001-1533 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
Be the first to add a field note for this CVE — a mitigation you’ve verified, a version caveat, or a link to a working fix. Sign in above to contribute.
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