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5.3

Microsoft ISA Server 2000 can be overwhelmed by UDP floods

CVE-2001-1533 · published 24 years ago
Summary

The 2000 version of Microsoft’s Internet Security and Acceleration Server can stop responding if an attacker sends a huge number of fragmented UDP messages, a type of network traffic. This can make the server unavailable to legitimate users. Reduce the risk by applying any available updates, limiting or blocking UDP traffic, and monitoring for unusually high network loads.

What to do

The CVE record does not list a fixed version. Check the vendor's site or the advisory links below - a fix may already be released.

Affected software
VendorProductAffected versions
microsoft isa_server 2000
cpe:2.3:a:microsoft:isa_server:2000:*:*:*:*:*:*:*
Original advisory text
Microsoft 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, say...
Microsoft 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
References
Fix within
Internet-facing 14 days
Internal 60 days
  • Not known to be exploited
  • Can be exploited automatically
  • Gives an attacker partial control
Severity
5.3 Medium
Exploitation
18% chance of attack within 30 days
Timeline
Published31 Dec 2001
Updated4 Nov 2026
First seen29 Sep 2026
Sources
CVE-2001-1533 · NVD
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