CVE-1999-0116
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 · uneditedDenial of service when an attacker sends many SYN packets to create multiple connections without ever sending an ACK to complete the connection, aka SYN flood.
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 confidenceA classic TCP SYN flood attack exploits the three-way handshake by sending numerous SYN packets without ever sending the corresponding ACK to complete the connection. This leaves the server with accumulating half-open connections that consume memory and fill the TCP backlog queue, eventually preventing legitimate clients from establishing new connections.
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= 3.2.5= 4.1= 4.2= 2.1= 2.2CVSS 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 checksWork through these to decide whether this CVE applies to you.
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Identify the installed IBM AIX or SNG versionRun 'oslevel' on AIX or check system documentation for SNG version. Compare the output against the affected versions: AIX 3.2.5, 4.1, 4.2 or SNG 2.1, 2.2.Affected if The system is running exactly one of the listed versions.
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Confirm TCP stack is reachable and exposedVerify the system has active TCP listening services using 'netstat -an | grep LISTEN' or 'ss -tlnp'. This confirms the TCP stack is accepting connections and could be targeted.Affected if The system has open TCP ports accepting connections.
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Check if SYN cookies are enabledOn AIX, use 'no -a | grep -i syncookie' or check the 'tcp_syncookies' network option. On SNG, review the TCP configuration for SYN cookie or equivalent protection settings.Affected if SYN cookies are disabled or not available (common for these older versions).
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Verify SYN backlog queue configurationOn AIX, run 'no -a | grep tcp' to review tcp_syn_rcv_queue_limit or equivalent backlog settings. Check if the queue is sized at default high values.Affected if The TCP backlog queue is configured to default high values and SYN cookies are disabled.
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Check SYN-received timeout configurationOn AIX, review 'no -a' output for tcp_syn_rcv_timeout or similar timeout parameters. Default timeouts in these versions are typically 60 seconds or higher.Affected if The SYN-received timeout is set to default values (typically 60+ seconds) with no rate limiting configured.
A system is affected if it is running IBM AIX 3.2.5, 4.1, or 4.2 (or SNG 2.1/2.2), has exposed TCP services, and has SYN cookies disabled with default SYN backlog and timeout settings.
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 dataEnable SYN cookies (or equivalent) on affected systems, reduce SYN-received timeout values, and implement SYN rate limiting at network edge devices or firewalls to drop or throttle suspicious traffic patterns.
- Consultation1.0 h
- Implementation2.0 h
- Testing1.0 h
- Review / QA1.0 h
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Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-1999-0116 — 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-1999-0116 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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- 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
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