CVE-1999-0077
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 · uneditedPredictable TCP sequence numbers allow spoofing.
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 · moderate confidenceThis vulnerability stems from early TCP/IP implementations that used predictable, incremental sequence numbers. Attackers could exploit this predictability to spoof TCP connections, potentially enabling session hijacking or man-in-the-middle attacks by guessing or calculating valid sequence numbers.
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= 4.0CVSS 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
- None
- Availability
- None
AV:N/AC:L/Au:N/C:P/I:N/A:N
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 checksWork through these to decide whether this CVE applies to you.
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Verify Windows NT versionRun 'winver' from Start > Run, or check System in Control Panel to confirm the exact Windows version and build numberAffected if The system is running any version of Windows NT 4.0 (all builds are affected)
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Confirm TCP/IP stack is loadedOpen Network applet in Control Panel, go to Protocols tab, verify TCP/IP Protocol is bound to at least one network adapterAffected if TCP/IP protocol is installed and bound to a network adapter - this is required for the vulnerability to be exploitable
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Check for exposed TCP listening servicesRun 'netstat -an' from command prompt and review output for LISTENING states on any portAffected if The system has any TCP service listening on any port (these would be potential targets for sequence number guessing)
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Verify network exposureDetermine if the affected NT 4.0 system has direct Internet exposure or is behind a properly configured firewall/NATAffected if The NT 4.0 system with TCP/IP enabled is directly accessible from untrusted networks without firewall protection
A system is affected only if it is running Windows NT 4.0 with the TCP/IP protocol stack loaded and has TCP services exposed to a network where an attacker could attempt sequence number prediction.
Generated from the published advisory. Verify against your own configuration.
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 dataModern systems implement RFC 1948 random sequence number generation, which mitigates this vulnerability. Organizations should ensure all systems and network devices run current, supported software versions with up-to-date TCP/IP stacks.
- Consultation2.0 h
- Testing1.0 h
- Review / QA1.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $1,200.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-1999-0077 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-1999-0077 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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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.
- 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