FreeBSDOperating system
CVE-1999-0796
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 · uneditedFreeBSD T/TCP Extensions for Transactions can be subjected to spoofing attacks.
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 affects FreeBSD's implementation of T/TCP (TCP Extensions for Transactions), a protocol designed to reduce latency for transaction-oriented traffic. The flaw allows remote attackers to perform spoofing attacks by forging TCP packets due to inadequate validation or weak sequence number handling in the T/TCP implementation.
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
FreeBSDOperating system
= 2.1.0= 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
- Partial
- Integrity
- Partial
- Availability
- Partial
AV:N/AC:L/Au:N/C:P/I:P/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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Check FreeBSD versionRun 'uname -a' or 'sysctl kern.osreldate' to determine the installed FreeBSD versionAffected if The system runs FreeBSD 2.1.0 or FreeBSD 2.2 (specifically versions matching the = 2.1.0 or = 2.2 notation)
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Verify T/TCP kernel module is loadedCheck if the T/TCP kernel module is loaded by examining kernel module list with 'kldstat' or checking for presence of tcpcc.ko or similar T/TCP-related kernel objectsAffected if T/TCP kernel support is compiled into or loaded by the kernel
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Check T/TCP sysctl controlRun 'sysctl -a | grep rfc1644' or directly 'sysctl net.inet.tcp.rfc1644' to query the T/TCP enable/disable settingAffected if net.inet.tcp.rfc1644 is set to 1 (enabled) - a value of 0 means T/TCP is disabled
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Inspect kernel configuration for T/TCPIf kernel source is available, examine the kernel configuration file (e.g., in /sys/i386/conf/) for options like 'TCPCC' or 'TCP_TRANSACTIONS' or grep the kernel source for 'rfc1644' or 'T/TCP' referencesAffected if The kernel is compiled with T/TCP (TCPCC or transaction-oriented TCP options) enabled
A system is affected if it runs FreeBSD 2.1.0 or 2.2 AND has T/TCP enabled (net.inet.tcp.rfc1644 set to 1 or T/TCP compiled into the kernel), as the vulnerability requires both the vulnerable version and active T/TCP support to be exploitable.
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 dataDisable T/TCP support in FreeBSD systems via kernel configuration (set `net.inet.tcp.rfc1644=0`) or apply period-appropriate patches from 1999. Alternatively, implement network filtering to reject T/TCP packets at the perimeter.
Fix this in FreeBSD
Scoped from the published advisory
- Consultation1.0 h
- Implementation2.0 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 $1,424.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-1999-0796 — 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-1999-0796 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
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