CVE-2026-41579 runc /dev Symlink Host File Modification Vulnerability
runc is a CLI tool for spawning and running containers according to the OCI specification. In versions prior to 1.3.6, 1.4.0-rc.1, 1.4.0-rc.12, 1.5.0-rc.1, and 1.5.0-rc.1, when setting up the container rootfs, setupPtmx and setupDevSymlinks call os.Remove and os.Symlink with a filepath.Join string which allow an image with /dev as a symlink to trick runc into deleting files called ptmx on the host or creating a hardcoded set of symlinks with specific names and targets in an arbitrary pre-existing host directory. This issue is not exploitable under Docker, because Docker creates a top-level read-only layer that masks any malicious /dev symlink present in the container image — unlike some other Linux container tooling, whose higher-level runtimes built on runc remain exposed to exploitation via a malicious image. This issue has been fixed in versions 1.3.6, 1.4.3 and 1.5.0.
Quick answer
OpenContainers runc should be reviewed and updated if it matches the affected versions. The recommended fix is to apply the vendor-supported patched version or the mitigation steps below, then retest the public website with Fixnx.
Who is affected
Affected versions
- < 1.3.6
- >= 1.4.0-rc.1, < 1.4.3
- >= 1.5.0-rc.1, < 1.5.0-rc.3
Fixed versions
- 1.3.6
- 1.4.3
- 1.5.0
How to fix it
runc is affected by this security issue. The safest fix is to update to the fixed version, then test the site or service again to make sure the risky path is closed.
- Find every place where runc is installed or used.
- Update to 1.3.6, 1.4.3, 1.5.0 or a later vendor-supported version.
- Back up the site or service before changing production systems.
- Apply the update in staging first if possible, then deploy it to production.
- If you cannot update right away, restrict access to the affected feature and monitor logs closely.
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Verify the fix
- Confirm the installed version is no longer in the affected range.
- Retest the affected page, API, upload, login, chat, container, or network flow.
- Check logs after the change for blocked attempts, crashes, or errors.
- Run a fresh Fixnx scan and save the report.
Related categories
Trusted references
FAQ
What is affected by CVE-2026-41579?
OpenContainers runc versions listed as affected should be reviewed: < 1.3.6, >= 1.4.0-rc.1, < 1.4.3, >= 1.5.0-rc.1, < 1.5.0-rc.3.
What should I fix first?
Start with internet-facing sites, admin panels, login flows, plugins, themes, modules, packages, and systems that process user-controlled input or sensitive data.
How do I confirm the fix worked?
Apply the patched version or mitigation, clear caches where relevant, retest the affected workflow, and run a new Fixnx scan to verify public website exposure signals.
How are Fixnx security risk categories chosen?
Fixnx keeps one canonical risk page and assigns only broad, relevant categories such as ecosystem, technology area, or vulnerability class.