Linux KernelOperating system · Linux
CVE-1999-0656
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 · uneditedThe ugidd RPC interface, by design, allows remote attackers to enumerate valid usernames by specifying arbitrary UIDs that ugidd maps to local user and group names.
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 confidenceThe ugidd RPC daemon maps UIDs to local user and group names and returns them to requesting clients. By design, this allows remote attackers to enumerate valid usernames by querying arbitrary UIDs, revealing which accounts exist on the system.
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
Linux KernelOperating system
all versionsCVSS 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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Check if ugidd daemon is runningRun 'ps aux | grep ugidd' or 'systemctl status rpc.nfsd' (note: ugidd may be part of nfs-utils package). Also check with 'rpcinfo -p' to see if the 'ugidd' program is registered.Affected if The ugidd RPC daemon process is actively running on the system
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Verify if RPC port 111 is listening and exposedRun 'netstat -anp | grep 111' or 'ss -anp | grep 111' to check if the RPC portmapper is listening on external interfaces.Affected if Port 111 is listening on a publicly accessible network interface (0.0.0.0 or non-loopback IP)
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Test RPC service enumeration capabilityFrom an external system or locally, run 'rpcinfo -p <target>' to query the RPC portmapper and look for program number 570027937 (ugidd). Alternatively, use 'showmount -e <target>' to test NFS-related RPC exposure.Affected if The RPC portmapper responds to external queries and exposes ugidd or related NFS RPC services
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Check firewall rules for RPC port 111Inspect firewall configuration: 'iptables -L -n' or 'firewall-cmd --list-all' to see if port 111/tcp and 111/udp are explicitly blocked or filtered.Affected if No firewall rule blocks or restricts access to port 111 from untrusted networks
The system is vulnerable if the ugidd RPC daemon is running AND port 111 is accessible from untrusted networks, allowing remote attackers to enumerate valid user accounts by querying UIDs.
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 the ugidd service if running, and restrict RPC port 111 access through firewall rules or TCP wrappers to prevent unauthorized enumeration queries.
Fix this in Linux Kernel
Scoped from the published advisory
- Consultation1.0 h
- Implementation1.0 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-1999-0656 — 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-1999-0656 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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- Version or environment caveats, and links to real fixes
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