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Ubuntu LinuxOperating system · Canonical

CVE-2020-11935

MEDIUM · 5.5 CVSS v3.1 Published 2023-04-07
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
57/100
Remediation priority · Elevated
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
It was discovered that aufs improperly managed inode reference counts in the vfsub_dentry_open() method. A local attacker could use this vulnerability to cause a denial of service 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 · moderate confidence

This vulnerability exists in aufs (advanced multi-layered unification filesystem), a Linux kernel module that implements a union mount filesystem. The issue is in the vfsub_dentry_open() function where inode reference counts are improperly managed, leading to potential memory corruption or leak. A local attacker could exploit this to cause a denial of service by triggering the improper reference counting.

MitigationUpdate the aufs package or kernel module to a version that includes the fix for proper inode reference count management in vfsub_dentry_open(). Consider restricting local unprivileged access to aufs operations as a compensating control until patching is feasible.

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
Affected:= 14.04= 16.04= 18.04= 20.04
Debian LinuxOperating system
Affected:= 10.0

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
Privileges
Low
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/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 checks

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

  1. Check if aufs kernel module is loaded
    Run 'lsmod | grep aufs' to see if the aufs module is currently loaded in the kernel
    Affected if The module is loaded (output shows aufs)
  2. Check for installed aufs package on Ubuntu
    Run 'dpkg -l | grep aufs' to list installed aufs packages and their versions
    Affected if An aufs package is installed with a version matching Ubuntu 14.04, 16.04, 18.04, or 20.04
  3. Check for aufs utilities on Debian
    Run 'dpkg -l | grep aufs' on Debian systems to identify installed aufs packages
    Affected if An aufs package is installed on Debian 10.0
  4. Verify aufs mount capability
    Run 'grep -q aufs /proc/filesystems && mount | grep aufs' to check if aufs can be used and if any aufs filesystems are currently mounted
    Affected if aufs appears in /proc/filesystems and is actively mounted

Your environment is affected if the aufs kernel module is loaded or any aufs package is installed on Ubuntu 14.04-20.04 or Debian 10.0, as these versions contain the vulnerable vfsub_dentry_open() function with improper inode reference counting.

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.

dbcve · scoped
Mitigation available No clean upgrade yet — mitigate in the meantime
Mitigation

Update the aufs package or kernel module to a version that includes the fix for proper inode reference count management in vfsub_dentry_open(). Consider restricting local unprivileged access to aufs operations as a compensating control until patching is feasible.

Recommended fix Moderate confidence

Update to the latest Ubuntu/Debian security releases for your version (kernel and aufs updates via standard apt repository)

  1. Run 'sudo apt-get update' to refresh package lists
  2. Run 'sudo apt-get upgrade' to install all available security updates, which will include the patched aufs/linux-image packages
  3. Reboot the system to load the updated kernel with the fixed aufs module
  4. Verify the fix by checking 'dpkg -l | grep aufs' shows the updated package version, or check the running kernel version with 'uname -r'
Caveat Kernel updates may require system reboot and could have compatibility implications with custom kernel modules

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Ubuntu Linux Scoped from the published advisory
  • Consultation2.0 h
  • Implementation4.0 h
  • Testing6.0 h
  • Review / QA3.0 h
15.0 hours of engineering $2,560
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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-2020-11935 in production — separate from our analysis above.

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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
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  • Version or environment caveats, and links to real fixes
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