CVE-2021-21284 privilege escalation in Moby

What is CVE-2021-21284?

CVE-2021-21284 is a medium-severity vulnerability in Debian Debian Linux, published on 2 Feb 2021. It can only be exploited from the same machine or local network, with no action from the victim.

Official description

In Docker before versions 9.03.15, 20.10.3 there is a vulnerability involving the --userns-remap option in which access to remapped root allows privilege escalation to real root. When using "--userns-remap", if the root user in the remapped namespace has access to the host filesystem they can modify files under "/var/lib/docker/<remapping>" that cause writing files with extended privileges. Versions 20.10.3 and 19.03.15 contain patches that prevent privilege escalation from remapped user.

Weakness: CWE-22

Which versions are affected by CVE-2021-21284?

4 open source packages ship an affected version, including github.com/moby/moby. It affects 3 products.

Products include Debian Debian Linux, Docker Docker, Netapp E-Series Santricity Os Controller.

How do I fix CVE-2021-21284?

Upgrade github.com/moby/moby to a fixed version for your release line: 19.3.15 or 20.10.3.

Is CVE-2021-21284 being exploited?

There is no known exploitation of CVE-2021-21284 in the wild and no public exploit code.

Other vulnerabilities in Debian Debian Linux

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• CVE-2025-49113 RoundCube Webmail Deserialization of Untrusted Data Exploited Critical 9.9
• CVE-2026-24061 GNU InetUtils Argument Injection Exploited Critical 9.8
• CVE-2025-39682 Linux Kernel Improper Check for Unusual or Exceptional Conditions Exploited Critical 9.8
• CVE-2024-9680 Mozilla Firefox Use-After-Free Exploited Critical 9.8

All Debian Debian Linux vulnerabilities

Sources

• CVE record
• NVD
• OSV
• GitHub advisory
• How this page is made

Also known as CLEANSTART-2026-QN82133, DEBIAN-CVE-2021-21284, GHSA-7452-xqpj-6rpc, UBUNTU-CVE-2021-21284.