dbcve.org
Internet Information ServerApplication · Microsoft

CVE-1999-1591

HIGH · 7.5 CVSS v2.0 Published 1999-12-31
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
84/100
Remediation priority · High
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
Microsoft Internet Information Services (IIS) server 4.0 SP4, without certain hotfixes released for SP4, does not require authentication credentials under certain conditions, which allows remote attackers to bypass authentication requirements, as demonstrated by connecting via Microsoft Visual InterDev 6.0.

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

This is an authentication bypass vulnerability in Microsoft Internet Information Services (IIS) 4.0 Service Pack 4. Without certain hotfixes released for SP4, the server fails to require authentication credentials under certain conditions, allowing remote attackers to bypass authentication. The vulnerability was demonstrated via connections from Microsoft Visual InterDev 6.0.

MitigationApply the relevant Microsoft hotfixes for IIS 4.0 SP4 that address the authentication bypass, or migrate to a supported IIS version. Given this is a 1999 vulnerability, any remaining affected systems should be urgently retired or isolated.

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
Visual InterdevApplication
Affected:= 6.0

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
Partial
Integrity
Partial
Availability
Partial

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

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. Confirm IIS version
    Check if Microsoft Internet Information Server 4.0 is installed. In Windows NT 4.0, open Control Panel > Services, look for 'Microsoft Internet Information Server' service, or check the registry key HKLM\SOFTWARE\Microsoft\InetStp for the VersionString value.
    Affected if The version reported is 4.0 (specifically without any additional hotfixes applied)
  2. Verify Windows NT 4.0 Service Pack level
    Run 'winver' from the command line or check System Properties to see the Windows NT version and service pack. Alternatively, check the registry key HKLM\SOFTWARE\Microsoft\Windows NT\CurrentVersion\CSDVersion.
    Affected if The system is Windows NT 4.0 with Service Pack 4 applied (CSDVersion shows 'Service Pack 4')
  3. Check for missing authentication bypass hotfixes
    Check the registry for installed hotfixes. Look in HKLM\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Hotfix for entries related to this authentication bypass issue. On IIS 4.0, you can also use the IIS Hotfix Checking Tool or inspect the metabase for security-related updates.
    Affected if The relevant hotfixes for CVE-1999-1591 are not present in the installed hotfix list, meaning SP4 is applied without subsequent security updates
  4. Test Visual InterDev connection behavior
    If Visual InterDev 6.0 is in use, observe whether authentication is being bypassed during remote debugging or project connection to IIS. A successful connection without prompted credentials may indicate the vulnerability.
    Affected if Visual InterDev 6.0 connects to IIS 4.0 SP4 without requiring authentication credentials

A system is affected if it runs Microsoft IIS 4.0 on Windows NT 4.0 Service Pack 4 without the specific authentication bypass hotfixes applied.

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.

From vendor data
Mitigation available No clean upgrade yet — mitigate in the meantime
Mitigation

Apply the relevant Microsoft hotfixes for IIS 4.0 SP4 that address the authentication bypass, or migrate to a supported IIS version. Given this is a 1999 vulnerability, any remaining affected systems should be urgently retired or isolated.

Fix this in Internet Information Server Scoped from the published advisory
  • Consultation2.0 h
  • Implementation4.0 h
  • Testing2.0 h
  • Review / QA1.0 h
9.0 hours of engineering $1,600
Get help mitigating

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $2,560.

Scan for this in your stack

Free · runs locally
dbcve dependency scanner

Check whether your project pulls in CVE-1999-1591 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.

Get it on GitHub Scan in the browser

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-1999-1591 in production — separate from our analysis above.

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.

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