runc 1.3.6 -- "On no account should you allow a Vogon to read poetry at you."

This is the sixth patch release of the 1.3.z series of runc. Among some
performance improvements and bugfixes, it includes a fix for a
low-severity vulnerability (CVE-2026-41579) and users are encouraged to
update. As it was a low-severity vulnerability and it was reported by
multiple people, we decided to release it publicly with NO EMBARGO.

Security

This release includes a fix for the following low-severity security issue:

• CVE-2026-41579 allowed a malicious image with a /dev symlink to have
  limited write access to the host filesystem in ways that our analysis
  indicates was too limited to be problematic in practice. This bug was very
  similar to those fixed in CVE-2025-31133, CVE-2025-52565,
  CVE-2025-31133 and was simply missed at the time when we hardened the
  rootfs preparation code. We have conducted a deeper audit and not found any
  other problematic cases.

  This patchset required backports for #5190 and #5285, which were primarily
  code reorganisations that were already backported to runc 1.4 and 1.5.

Fixed

• A regression in runc v1.3.0 which can result in a stuck runc exec or
  runc run when the container process runs for a short time. (#5208,
  #5210, #5215)
• Various integration test improvements. (#5159, #5188, #5226, #5228, #5239,
  #5253, #5269, #5288)

Changed

• When masking directories with maskPaths, runc will now re-use a single
  tmpfs instance (which is not writable) to reduce the number tmpfs
  superblocks that need to be reaped when containers die (in particular,
  Kubernetes applies masks to per-CPU sysfs directories which get expensive
  quickly). (#5275, #5281)

Static Linking Notices

The runc binary distributed with this release are statically linked with
the following GNU LGPL-2.1 licensed libraries, with runc acting
as a "work that uses the Library":

• libseccomp

The versions of these libraries were not modified from their upstream versions,
but in order to comply with the LGPL-2.1 (§6(a)), we have attached the
complete source code for those libraries which (when combined with the attached
runc source code) may be used to exercise your rights under the LGPL-2.1.

However we strongly suggest that you make use of your distribution's packages
or download them from the authoritative upstream sources, especially since
these libraries are related to the security of your containers.

---

Thanks to the following contributors for making this release possible:

• Aleksa Sarai cyphar@cyphar.com
• Ayato Tokubi atokubi@redhat.com
• Davanum Srinivas davanum@gmail.com
• Kevin Berry kpberry11@gmail.com
• Kir Kolyshkin kolyshkin@gmail.com
• Ricardo Branco rbranco@suse.de
• Rodrigo Campos Catelin rodrigo@amutable.com
• Li Fubang lifubang@acmcoder.com

Signed-off-by: Aleksa Sarai cyphar@cyphar.com