CVE-2026-41579: CWE-61: UNIX Symbolic Link (Symlink) Following in opencontainers runc
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.
AI Analysis
Technical Summary
In opencontainers runc versions before 1.3.6, 1.4.3, and 1.5.0, the setupPtmx and setupDevSymlinks functions use os.Remove and os.Symlink on paths constructed with filepath.Join. If a container image contains /dev as a symlink, this can trick runc into deleting host files named ptmx or creating symlinks with specific names and targets in arbitrary existing host directories. Docker mitigates this by applying a top-level read-only layer that masks malicious /dev symlinks, but other container runtimes built on runc may remain vulnerable. The issue is tracked as CVE-2026-41579 and classified under CWE-61 (Improper Handling of Symbolic Links).
Potential Impact
The vulnerability allows a container image to manipulate host filesystem objects by exploiting symlink handling during container rootfs setup. This can lead to unauthorized deletion or creation of files on the host, impacting host integrity. However, the impact is limited as it requires local access (attack vector is local), user interaction, and low privileges, and it does not affect confidentiality or availability. Docker users are not affected due to its protective layering.
Mitigation Recommendations
Upgrade runc to version 1.3.6, 1.4.3, 1.5.0 or later, where this vulnerability has been fixed. If using Docker, this issue is not exploitable due to Docker's top-level read-only layer. For other container runtimes built on runc, ensure they use patched runc versions or apply equivalent mitigations to prevent symlink-based host filesystem manipulation.
CVE-2026-41579: CWE-61: UNIX Symbolic Link (Symlink) Following in opencontainers runc
Description
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.
CVSS v3.1
Score 3.3low
Affected software
pkg:github/opencontainers/runcRun on your own infrastructure? Check whether these packages are installed with threat-finder — our free open-source scanner.
Weaknesses
AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
In opencontainers runc versions before 1.3.6, 1.4.3, and 1.5.0, the setupPtmx and setupDevSymlinks functions use os.Remove and os.Symlink on paths constructed with filepath.Join. If a container image contains /dev as a symlink, this can trick runc into deleting host files named ptmx or creating symlinks with specific names and targets in arbitrary existing host directories. Docker mitigates this by applying a top-level read-only layer that masks malicious /dev symlinks, but other container runtimes built on runc may remain vulnerable. The issue is tracked as CVE-2026-41579 and classified under CWE-61 (Improper Handling of Symbolic Links).
Potential Impact
The vulnerability allows a container image to manipulate host filesystem objects by exploiting symlink handling during container rootfs setup. This can lead to unauthorized deletion or creation of files on the host, impacting host integrity. However, the impact is limited as it requires local access (attack vector is local), user interaction, and low privileges, and it does not affect confidentiality or availability. Docker users are not affected due to its protective layering.
Mitigation Recommendations
Upgrade runc to version 1.3.6, 1.4.3, 1.5.0 or later, where this vulnerability has been fixed. If using Docker, this issue is not exploitable due to Docker's top-level read-only layer. For other container runtimes built on runc, ensure they use patched runc versions or apply equivalent mitigations to prevent symlink-based host filesystem manipulation.
Technical Details
- Data Version
- 5.2
- Assigner Short Name
- GitHub_M
- Date Reserved
- 2026-04-21T14:15:21.958Z
- Cvss Version
- 3.1
- State
- PUBLISHED
- Remediation Level
- null
Threat ID: 6a446bac27e9c79719c24386
Added to database: 07/01/2026, 01:21:48 UTC
Last enriched: 07/08/2026, 12:48:53 UTC
Last updated: 08/13/2026, 18:25:01 UTC
Views: 147
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