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OutlookApplication · Microsoft

CVE-1999-1164

MEDIUM · 5.0 CVSS v2.0 Published 1999-06-25
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
59/100
Remediation priority · Elevated
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 Outlook client allows remote attackers to cause a denial of service by sending multiple email messages with the same X-UIDL headers, which causes Outlook to hang.

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

Microsoft Outlook email client contains a denial of service vulnerability where processing multiple email messages with identical X-UIDL headers causes the client to hang, rendering it unresponsive.

MitigationApply available Microsoft security patches for the affected Outlook versions or implement mail server-side filtering to detect and block emails with duplicate X-UIDL headers.

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
OutlookApplication
Affected:= 97= 98= 2000
Outlook ExpressApplication
Affected:all versions

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
None
Integrity
None
Availability
Partial

AV:N/AC:L/Au:N/C:N/I:N/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. Identify Outlook version
    Open Microsoft Outlook, go to Help > About Microsoft Outlook to view the version number. Alternatively, check the registry key HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Office\<version>\Outlook\InstallRoot if available.
    Affected if The installed version is 97, 98, or 2000
  2. Identify Outlook Express version
    Open Microsoft Outlook Express, go to Help > About Microsoft Outlook Express to view the version number.
    Affected if Any version of Microsoft Outlook Express is installed (all versions are affected)
  3. Confirm email processing is active
    Verify the email client has been configured with at least one mail account and is capable of receiving or has received email messages.
    Affected if The client is actively used for email processing and can receive messages containing X-UIDL headers

A user is affected if they are running Microsoft Outlook versions 97, 98, or 2000, or any version of Microsoft Outlook Express, and use the client to process emails with X-UIDL headers present.

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 available Microsoft security patches for the affected Outlook versions or implement mail server-side filtering to detect and block emails with duplicate X-UIDL headers.

Fix this in Outlook 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.

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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-1999-1164 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