CVE-2023-3777

Published: 3 August 2023

A use-after-free vulnerability in the Linux kernel's netfilter: nf_tables component can be exploited to achieve local privilege escalation. When nf_tables_delrule() is flushing table rules, it is not checked whether the chain is bound and the chain's owner rule can also release the objects in certain circumstances. We recommend upgrading past commit 6eaf41e87a223ae6f8e7a28d6e78384ad7e407f8.

From the Ubuntu Security Team

Kevin Rich discovered that the netfilter subsystem in the Linux kernel did not properly handle table rules flush in certain circumstances. A local attacker could possibly use this to cause a denial of service (system crash) or execute arbitrary code.

Notes

Priority reason:
By using unprivileged user namespaces, this can be exploited to achieve local privilege escalation.

Google kCTF submission

Mitigation

If not needed, disable the ability for unprivileged users
to create namespaces. To do this temporarily, do:
  sudo sysctl -w kernel.unprivileged_userns_clone=0
To disable across reboots, do:
  echo kernel.unprivileged_userns_clone=0 | \
  sudo tee /etc/sysctl.d/99-disable-unpriv-userns.conf

Status

Severity score breakdown

References

• https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2023-3777
• https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=6eaf41e87a223ae6f8e7a28d6e78384ad7e407f8
• https://google.github.io/security-research/kernelctf/rules
• https://patchwork.ozlabs.org/project/netfilter-devel/patch/20230720071721.14777-1-pablo@netfilter.org/
• https://ubuntu.com/security/notices/USN-6315-1
• https://ubuntu.com/security/notices/USN-6316-1
• https://ubuntu.com/security/notices/USN-6318-1
• https://ubuntu.com/security/notices/USN-6321-1
• https://ubuntu.com/security/notices/USN-6325-1
• https://ubuntu.com/security/notices/USN-6328-1
• https://ubuntu.com/security/notices/USN-6330-1
• https://ubuntu.com/security/notices/USN-6332-1
• https://ubuntu.com/security/notices/USN-6348-1
• https://ubuntu.com/security/notices/USN-6385-1
• NVD
• Launchpad
• Debian