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Date: Thu, 1 Feb 2024 07:33:01 +1100
From: Aleksa Sarai <>
Subject: runc: CVE-2024-21626: high severity container breakout attack

NOTE: This advisory was sent to <>
two weeks ago. If you ship any Open Container Initiative software, we
highly recommend that you subscribe to our security-announce list in
order to receive more timely disclosures of future security issues. The
procedure for subscribing to security-announce is outlined here[1].


This is a notification to vendors that use runc about a high-severity
vulnerability (CVE-2024-21626) with several exploit methods which allow
for full container breakouts due to an internal file descriptor leak.

Attached are patches which resolve this issue and provide further
hardening to prevent similar issues from happening in the future. The
provided patches apply cleanly on top of runc 1.1.11. We have also
released runc 1.1.12[3] with these patches applied.

The most severe version of this issue is assigned a CVSS of
CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:H (8.6 -- High severity). For
a full breakdown of the CVSS scoring for each sub-issue, please read
through the advisory[2] which describes each attack in more detail.

The core issue is a file descriptor leak, and while we do O_CLOEXEC all
file descriptors before executing the container code, the file
descriptor is open when doing setcwd(2) which means that the reference
can be kept alive into the container by configuring the working
directory to be a path resolved through the file descriptor (and the
non-dumpable bit is unset after execve(2) meaning that there are
multiple ways to attack this other than bad configurations).

There is also an execve(2)-based attack that makes simple verification
unworkable and was particularly hairy to fix (the patch involves doing
//go:linkname to access Go runtime internals, because the only way to
defend against it entirely is to close all unneeded file descriptors --
for the same reason that #!-based tricks meant that CVE-2019-5736
required drastic measures).

Aside from only running trusted images and never using "runc exec" on
containers, there are no generic workarounds for the issue and so users
are strongly advised to patch their installations as soon as possible.
Usage of user namespaces and LSMs like SELinux will reduce the impact of
a container breakout (and we recommend using them) but do not stop it
from happening entirely.

Credit for discovering and reporting the original vulnerability goes to
Rory McNamara from Snyk. In addition, credit goes to @lifubang from
acmcoder and Aleksa Sarai from SUSE for discovering how to adapt the
attacks in various ways to make them more severe and practical for real
SaaS workloads.

Please send any questions you have to <> or open
an issue on our issue tracker[4]. If you feel the issue is
security-sensitive please send a mail to <>.


Aleksa Sarai
Senior Software Engineer (Containers)
SUSE Linux GmbH

View attachment "0001-Fix-File-to-Close.patch" of type "text/x-patch" (1196 bytes)

View attachment "0002-init-verify-after-chdir-that-cwd-is-inside-the-conta.patch" of type "text/x-patch" (6850 bytes)

View attachment "0003-setns-init-do-explicit-lookup-of-execve-argument-ear.patch" of type "text/x-patch" (2668 bytes)

View attachment "0004-init-close-internal-fds-before-execve.patch" of type "text/x-patch" (10463 bytes)

View attachment "0005-cgroup-plug-leaks-of-sys-fs-cgroup-handle.patch" of type "text/x-patch" (4160 bytes)

View attachment "0006-libcontainer-mark-all-non-stdio-fds-O_CLOEXEC-before.patch" of type "text/x-patch" (1922 bytes)

View attachment "0007-init-don-t-special-case-logrus-fds.patch" of type "text/x-patch" (2302 bytes)

Download attachment "signature.asc" of type "application/pgp-signature" (229 bytes)

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