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50 lines
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50 lines
2.4 KiB
Markdown
# CVE-2024-1086: kernel
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## Title
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CVE-2024-1086: kernel: nf_tables: use-after-free vulnerability in the nft_verdict_init() function
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## Summary
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As [briefly described by Red Hat](https://access.redhat.com/security/cve/CVE-2024-1086):
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A flaw was found in the Netfilter subsystem in the Linux kernel. This issue occurs in the `nft_verdict_init()` function, allowing positive values as a drop error within the hook verdict, therefore, the `nf_hook_slow()` function can cause a double-free vulnerability when `NF_DROP` is issued with a drop error that resembles `NF_ACCEPT`. The `nf_tables` component can be exploited to achieve local privilege escalation.
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Exploitation of the flaw is [described in great detail in a blog post by Notselwyn](https://pwning.tech/nftables/).
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Public disclosure date: March 26, 2024 for the above blog post, which made the issue widely known
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## EL9
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Affected. We will of course rebuild upstream's fix as soon as it arrives. Meanwhile, please refer to the mitigations below.
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## EL8
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- Fixed in version: `kernel-4.18.0-513.24.1.el8_9` available April 5, 2024
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- Errata: [RLSA-2024:1607](https://errata.rockylinux.org/RLSA-2024:1607) issued April 5, 2024
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## Mitigation
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Meanwhile, we recommend two mitigations:
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- If you don't use containers, we recommend that you disable user namespaces e.g. by running the below commands as root:
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```
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echo user.max_user_namespaces=0 > /etc/sysctl.d/userns.conf
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sysctl -p /etc/sysctl.d/userns.conf
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```
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This is a mitigation also suggested by Red Hat.
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It is sufficient to fully mitigate this and other/future related vulnerabilities.
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- If you cannot disable user namespaces, you may nevertheless be able to [disable network namespaces](https://www.openwall.com/lists/oss-security/2024/04/14/1), which is also sufficient to fully mitigate this and some other/future related vulnerabilities.
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- Install our [package of LKRG](../packages/lkrg.md), start and enable the service.
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This does not fully mitigate the vulnerability,
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but it reliably prevents the specific exploit referenced above from working and produces LKRG alerts when the exploit is run.
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LKRG's feature that does so is its allow list for the kernel's usermodehelper.
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This will similarly prevent other/future exploits that abuse usermodehelper.
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The remaining risks are Denial of Service (DoS) as even interrupted exploits may leave the system in an unstable state,
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and a different exploit of the same vulnerability bypassing LKRG.
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