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Exchange ServerApplication · Microsoft

CVE-2004-0840

HIGH · 10.0 CVSS v2.0 Published 2004-11-03
Patch available
A vendor patch is available. No clean upgrade release — apply the published patch.
See remediation →
100/100
Remediation priority · Urgent
Remotely reachable No privileges Zero-click Patch available

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
The SMTP (Simple Mail Transfer Protocol) component of Microsoft Windows XP 64-bit Edition, Windows Server 2003, Windows Server 2003 64-bit Edition, and the Exchange Routing Engine component of Exchange Server 2003, allows remote attackers to execute arbitrary code via a malicious DNS response message containing length values that are not properly validated.

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
How this class of weakness works · CWE-20

The application accepts input without confirming it is well-formed or within expected bounds, so malformed data can push the program into states its author never anticipated. Attackers probe these gaps to trigger crashes, bypass logic, or feed tainted values into more dangerous operations downstream. Remediating it well means validating and normalising every input at the boundary against a strict allow-list — not merely filtering known-bad values.

General guidance for the improper input validation class — the official description and references above are authoritative for this specific CVE. Want a bespoke review and a reviewed fix? Ask our team →

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
Exchange ServerApplication
Affected:= 2003
Windows Server 2003Operating system
Affected:all versions= r2
Windows XpOperating system
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
Complete
Integrity
Complete
Availability
Complete

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

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
Patch available Apply the vendor patch
Vendor patch www.kb.cert.org →
Recommended fix High confidence

Windows Server 2016/2019/2022 and Exchange Server 2016/2019; Windows 10/11 for workstations

  1. 1. Identify all systems running affected versions: Windows XP (all versions), Windows Server 2003 (all versions including R2), and Exchange Server 2003.
  2. 2. Because these products (Windows XP, Windows Server 2003, Exchange Server 2003) are all end-of-life and no longer receive security updates from Microsoft, migrate to supported operating systems and Exchange versions.
  3. 3. For Exchange Server workloads: migrate to a supported version of Exchange Server (Exchange Server 2016 or Exchange Server 2019) on supported Windows Server (Windows Server 2019 or 2022).
  4. 4. For Windows Server workloads: upgrade to a supported Windows Server version (Windows Server 2016, 2019, or 2022).
  5. 5. For Windows XP workstations: upgrade to a supported Windows version (Windows 10 or Windows 11).
  6. 6. Apply the principle of least privilege to SMTP services after migration.
  7. 7. Implement network segmentation to isolate SMTP/DNS services from untrusted networks as an additional defense-in-depth measure.
Caveat These are legacy systems from 2003-2004 era; migration to modern platforms will require significant planning, potential application compatibility testing, and possible reconfiguration of mail flow rules and connectors.

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

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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-2004-0840 in production — separate from our analysis above.

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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
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