CVE-1999-1203
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 · uneditedMultilink PPP for ISDN dialup users in Ascend before 4.6 allows remote attackers to cause a denial of service via a spoofed endpoint identifier.
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 confidenceVulnerability in Ascend multilink PPP implementations before version 4.6 allows remote attackers to cause denial of service by spoofing endpoint identifiers. The flaw exploits the Multilink PPP protocol used for aggregating multiple ISDN B-channels, where insufficient validation of endpoint identifier fields enables an attacker to disrupt active dialup sessions.
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<= 4.6CVSS 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 Ascend ISDN equipmentLocate Ascend branded ISDN routers or access servers in the network infrastructure. Check physical devices, network diagrams, or use SNMP to query device identification (sysDescr OID).Affected if The device is an Ascend ISDN multilink-capable system.
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Confirm Multilink PPP is enabledReview the device configuration for multilink PPP settings. On Ascend equipment, check for 'multilink' or 'multilink PPP' statements in the configuration, or inspect interface configurations for multilink bundle bindings.Affected if Multilink PPP protocol is actively configured on one or more ISDN interfaces.
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Check Ascend Multilink PPP versionAccess the Ascend device via console, telnet, or SSH and execute the command to display software version (commonly 'show version' or 'version' depending on the Ascend OS variant). Look for the Multilink PPP component version number.Affected if The displayed Multilink PPP version is 4.6 or earlier.
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Verify ISDN B-channel aggregationCheck that multiple ISDN B-channels are configured for multilink operation. Review the interface configuration to confirm multiple B-channels are bound to a multilink bundle for aggregate bandwidth.Affected if Multiple ISDN B-channels are actively aggregated using Multilink PPP.
A system is affected if it is an Ascend ISDN device with Multilink PPP enabled and the software version is 4.6 or earlier, allowing spoofed endpoint identifiers to disrupt active dialup sessions.
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 dataGiven this affects legacy ISDN infrastructure from the late 1990s, the primary remediation is retirement and replacement of any remaining Ascend ISDN equipment with modern networking hardware, as patches for such vintage systems are unlikely to be available.
- Consultation2.0 h
- Implementation8.0 h
- Testing3.0 h
- Review / QA2.0 h
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Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-1999-1203 — 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-1999-1203 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
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