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FreeBSDOperating system

CVE-1999-0963

HIGH · 7.2 CVSS v2.0 Published 1999-12-01
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
77/100
Remediation priority · High
No privileges Zero-click

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 · unedited
FreeBSD mount_union command allows local users to gain root privileges via a symlink attack.

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 confidence

This is a local privilege escalation vulnerability in FreeBSD's mount_union filesystem utility. The mount_union command improperly handles symbolic links during union mount operations, allowing a local attacker to manipulate the mount process via symlink attack to gain root privileges.

MitigationApply FreeBSD security patches for this vulnerability from 1999, or upgrade to a supported FreeBSD release that includes the fix. Restrict access to the mount_union utility to trusted administrative users only as a compensating control.

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
Affected:= 2.2

CVSS 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
Local
Complexity
Low
Authentication
None
Confidentiality
Complete
Integrity
Complete
Availability
Complete

AV:L/AC:L/Au:N/C:C/I:C/A:C

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 checks

Work through these to decide whether this CVE applies to you.

  1. Identify FreeBSD version
    Run 'uname -a' or check /etc/os-release (if available on older FreeBSD) to determine the exact FreeBSD release version
    Affected if The system is running FreeBSD 2.2.x (any patch level)
  2. Locate mount_union binary
    Run 'which mount_union' or 'ls -la /sbin/mount_union' to find the mount_union binary
    Affected if The mount_union binary exists on the system (vulnerable if using FreeBSD 2.2)
  3. Check mount_union binary permissions
    Run 'ls -la /sbin/mount_union' to view owner, group, and permission bits
    Affected if The binary is world-writable or has suspicious permissions allowing non-root execution
  4. Identify active union mounts
    Run 'mount | grep union' or check /etc/fstab for any union mount entries
    Affected if Any union mounts are currently active or configured in /etc/fstab

The system is affected if it is running FreeBSD 2.2.x and has the mount_union utility present, especially if union mounts are in use.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

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 data
Mitigation available No clean upgrade yet — mitigate in the meantime
Mitigation

Apply FreeBSD security patches for this vulnerability from 1999, or upgrade to a supported FreeBSD release that includes the fix. Restrict access to the mount_union utility to trusted administrative users only as a compensating control.

Fix this in FreeBSD Scoped from the published advisory
  • Consultation1.0 h
  • Implementation2.0 h
  • Testing1.0 h
  • Review / QA1.0 h
5.0 hours of engineering $890
Get help mitigating

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 locally
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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-1999-0963 in production — separate from our analysis above.

No notes yet

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What this is

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.

What belongs here
  • 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