high
8.8
CWE
682
Advisory Published
CVE Published
Updated
Advisory Published

CVE-2021-31440: Linux Kernel eBPF Improper Input Validation Privilege Escalation Vulnerability

First published: Fri May 21 2021(Updated: )

An out-of-bounds access flaw was found in the Linux kernel’s implementation of the eBPF code verifier, where an incorrect register bounds calculation while checking unsigned 32-bit instructions in an eBPF program occurs.. By default accessing the eBPF verifier is only accessible to privileged users with CAP_SYS_ADMIN. The issue results from the lack of proper validation of user-supplied eBPF programs prior to executing them. A local user could use this flaw to crash the system or possibly escalate their privileges on the system.

Credit: zdi-disclosures@trendmicro.com zdi-disclosures@trendmicro.com zdi-disclosures@trendmicro.com

Affected SoftwareAffected VersionHow to fix
redhat/kernel-rt<0:4.18.0-348.rt7.130.el8
0:4.18.0-348.rt7.130.el8
redhat/kernel<0:4.18.0-348.el8
0:4.18.0-348.el8
redhat/kernel<5.13
5.13
Linux Kernel>=5.7<5.10.37
Linux Kernel>=5.11<5.11.21
Linux Kernel>=5.12<5.12.4
netapp solidfire baseboard management controller firmware
netapp solidfire baseboard management controller
netapp cloud backup
NetApp H500S Firmware
netapp h500s
netapp h700s firmware
netapp h700s
netapp h300e firmware
netapp h300e
netapp h500e firmware
netapp h500e
netapp h700e firmware
netapp h700e
netapp h410s firmware
netapp h410s
netapp h300s firmware
netapp h300s
All of
netapp solidfire baseboard management controller firmware
netapp solidfire baseboard management controller
All of
NetApp H500S Firmware
netapp h500s
All of
netapp h700s firmware
netapp h700s
All of
netapp h300e firmware
netapp h300e
All of
netapp h500e firmware
netapp h500e
All of
netapp h700e firmware
netapp h700e
All of
netapp h410s firmware
netapp h410s
All of
netapp h300s firmware
netapp h300s
Linux kernel
debian/linux
5.10.223-1
5.10.226-1
6.1.123-1
6.1.128-1
6.12.12-1
6.12.15-1

Remedy

The default Red Hat Enterprise Linux kernel prevents unprivileged users from being able to use eBPF by the kernel.unprivileged_bpf_disabled sysctl. This would require a privileged user with CAP_SYS_ADMIN or root to be able to abuse this flaw reducing its attack space. For the Red Hat Enterprise Linux 7 the eBPF for unprivileged users is always disabled. For the Red Hat Enterprise Linux 8 to confirm the current state, inspect the sysctl with the command: # cat /proc/sys/kernel/unprivileged_bpf_disabled The setting of 1 would mean that unprivileged users can not use eBPF, mitigating the flaw. A kernel update will be required to mitigate the flaw for the root or users with CAP_SYS_ADMIN capabilities.

Remedy

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=10bf4e83167cc68595b85fd73bb91e8f2c086e36

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Reference Links

Parent vulnerabilities

(Appears in the following advisories)

Frequently Asked Questions

  • What is the severity of CVE-2021-31440?

    CVE-2021-31440 has a medium severity rating due to its potential impact on the Linux kernel's eBPF code verifier.

  • How do I fix CVE-2021-31440?

    To fix CVE-2021-31440, ensure you upgrade to the recommended kernel versions for your distribution.

  • What systems are affected by CVE-2021-31440?

    CVE-2021-31440 affects various Linux kernel versions including 4.18, 5.10, and 5.13, along with specific Red Hat kernel packages.

  • What is the nature of the vulnerability in CVE-2021-31440?

    CVE-2021-31440 is an out-of-bounds access flaw in the eBPF code verifier caused by incorrect register bounds calculation.

  • Is CVE-2021-31440 exploitable?

    Yes, CVE-2021-31440 can be exploited by crafting malicious eBPF programs that leverage the vulnerability.

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