CVE-1999-1591

CVE-1999-1591 is a high-severity vulnerability in Microsoft Internet Information Server with a CVSS 2.0 base score of 7.5. Its EPSS exploit-prediction score of 11% places it in the 95th percentile, indicating an elevated likelihood of exploitation.

Key facts

Description

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.

Frequently asked questions

What is CVE-1999-1591?
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.
How severe is CVE-1999-1591?
CVE-1999-1591 has a CVSS 2.0 base score of 7.5, rated high severity.
Is CVE-1999-1591 being actively exploited?
It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 11% (95th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-1999-1591?
CVE-1999-1591 primarily affects Microsoft Internet Information Server. In total, 2 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-1999-1591?
Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.
When was CVE-1999-1591 published?
CVE-1999-1591 was published on 1999-12-31 and last updated on 2026-06-16.

References

Affected products (2)

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