Ubuntu LinuxOperating system · Canonical
CVE-2018-6553
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 CUPS AppArmor profile incorrectly confined the dnssd backend due to use of hard links. A local attacker could possibly use this issue to escape confinement. This flaw affects versions prior to 2.2.7-1ubuntu2.1 in Ubuntu 18.04 LTS, prior to 2.2.4-7ubuntu3.1 in Ubuntu 17.10, prior to 2.1.3-4ubuntu0.5 in Ubuntu 16.04 LTS, and prior to 1.7.2-0ubuntu1.10 in Ubuntu 14.04 LTS.
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 CUPS AppArmor profile incorrectly confined the dnssd (DNS Service Discovery) backend due to use of hard links, allowing a local attacker to potentially escape AppArmor confinement and gain unauthorized access.
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
Ubuntu LinuxOperating system
= 14.04= 16.04= 17.10= 18.04
Debian LinuxOperating system
= 8.0= 9.0all 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
- Local
- Complexity
- Low
- Privileges
- Low
- User interaction
- None
- Scope
- Changed
- Confidentiality
- High
- Integrity
- High
- Availability
- High
CVSS:3.0/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H
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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Verify CUPS is installedCheck for CUPS package using your system package manager (e.g., dpkg -l cups, rpm -q cups, or which cupsd)Affected if CUPS is installed on the system
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Confirm AppArmor is enabledRun 'aa-status' or check /sys/kernel/security/apparmor/profiles to see if AppArmor is actively enforcing profilesAffected if AppArmor is enabled and enforcing profiles on the system
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Locate the CUPS AppArmor profileLook for the CUPS AppArmor profile in /etc/apparmor.d/ (typically usr.sbin.cupsd or usr.lib.cups)Affected if A CUPS AppArmor profile exists on the system
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Inspect the dnssd backend entry in the profileExamine the CUPS AppArmor profile for entries related to the dnssd backend (often found at /usr/lib/cups/backend/dnssd or /usr/libexec/cups/backend/dnssd)Affected if The profile contains a hard-linked reference to the dnssd backend rather than its direct path, indicating the vulnerability is present
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Check for hard links in the CUPS backend directoryUse 'ls -li /usr/lib/cups/backend/' (or /usr/libexec/cups/backend/) to list inodes and look for multiple filenames pointing to the same inode as the dnssd backendAffected if Hard links exist that incorrectly associate the dnssd backend with a different AppArmor profile confinement than intended
A system is affected if it runs CUPS with AppArmor enabled and the CUPS AppArmor profile contains hard-linked references to the dnssd backend that cause incorrect confinement.
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 dataUpdate CUPS to the patched versions specified for each Ubuntu release, which include the corrected AppArmor profile that properly confines the dnssd backend.
Fix this in Ubuntu Linux
Scoped from the published advisory
- Consultation3.0 h
- Implementation4.0 h
- Testing2.0 h
- Review / QA2.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $3,168.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2018-6553 — 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-2018-6553 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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