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Internet Information ServerApplication · Microsoft

CVE-1999-0874

HIGH · 10.0 CVSS v2.0 Published 1999-06-16
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
100/100
Remediation priority · Urgent
High EPSS Remotely reachable No privileges Zero-click

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 · unedited
Buffer overflow in IIS 4.0 allows remote attackers to cause a denial of service via a malformed request for files with .HTR, .IDC, or .STM extensions.

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 · high confidence

Buffer overflow vulnerability in Microsoft IIS 4.0 allows remote attackers to cause a denial of service by sending malformed HTTP requests targeting files with .HTR, .IDC, or .STM extensions. The overflow occurs during request processing for these server-side include file types.

MitigationApply available Microsoft patches for IIS 4.0, or migrate to a supported IIS version. As an interim measure, consider removing or blocking access to the vulnerable .HTR, .IDC, and .STM extension handlers if not required.

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
Internet Information ServerApplication
Affected:= 4.0
Windows 2000Operating system
Affected:all versions
Windows NtOperating system
Affected:all versions= 4.0

CVSS 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
Authentication
None
Confidentiality
Complete
Integrity
Complete
Availability
Complete

AV:N/AC:L/Au:N/C:C/I:C/A:C

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 checks

Work through these to decide whether this CVE applies to you.

  1. Identify IIS version
    Check the IIS metabase or registry for the version number. In IIS 4.0, open the IIS Manager, right-click the server, and view properties, or query the registry key HKLM\SYSTEM\CurrentControlSet\Services\W3SVC\Parameters\MajorVersion
    Affected if The installed IIS version is 4.0 specifically
  2. Identify the operating system
    Check the Windows version by running 'winver' or viewing System Properties. This vulnerability affects Windows NT 4.0 and Windows 2000
    Affected if The server is running Windows NT 4.0 or Windows 2000 with IIS installed
  3. Verify .HTR handler is present
    Check if the .HTR extension mapping exists in IIS. In IIS Manager, view the 'Home Directory' or 'Configuration' for the default website and look for a mapping to ISM.DLL for the .HTR extension
    Affected if The .HTR extension mapping to ISM.DLL is present and enabled
  4. Verify .IDC handler is present
    Check if the .IDC extension mapping exists in IIS. In IIS Manager, view the extension mappings and look for a mapping to IDQ.DLL or similar for the .IDC extension
    Affected if The .IDC extension mapping is present and enabled
  5. Verify .STM handler is present
    Check if the .STM extension mapping exists in IIS. In IIS Manager, view the extension mappings and look for a mapping to the STM handler
    Affected if The .STM extension mapping is present and enabled

A server is affected if it runs IIS 4.0 on Windows NT 4.0 or Windows 2000 with any of the .HTR, .IDC, or .STM extension handlers enabled.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

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.

dbcve · scoped
Mitigation available No clean upgrade yet — mitigate in the meantime
Mitigation

Apply available Microsoft patches for IIS 4.0, or migrate to a supported IIS version. As an interim measure, consider removing or blocking access to the vulnerable .HTR, .IDC, and .STM extension handlers if not required.

Recommended fix High confidence

Windows Server 2008 or later with current IIS version (IIS 7.0+)

  1. 1. Open the Internet Information Services (IIS) Manager console
  2. 2. Navigate to the website or virtual directory requiring protection
  3. 3. Right-click and select 'Properties'
  4. 4. Click the 'Configuration' button (or 'Home Directory' > 'Configuration')
  5. 5. In the 'App Mappings' tab, locate and remove entries for .HTR, .IDC, and .STM extensions
  6. 6. Alternatively, from command line: cscript adsutil.vbs set /w3svc/1/root/HtrScriptMap '' (for each extension)
  7. 7. Restart IIS using 'iisreset' command
  8. 8. Verify that requests to .HTR, .IDC, and .STM files return 404 or are denied
Caveat Removing ISAPI mappings will disable HTR, IDC, and STM functionality - verify no legacy applications depend on these extensions before removal. Migration to modern Windows Server requires application compatibility testing.

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Internet Information Server Scoped from the published advisory
  • Consultation4.0 h
  • Implementation16.0 h
  • Testing8.0 h
  • Review / QA4.0 h
32.0 hours of engineering $5,600
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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-1999-0874 in production — separate from our analysis above.

No notes yet

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What this is

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.

What belongs here
  • 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