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 Software | Affected Version | How 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 |
| Linux kernel | ||
| redhat/kernel | <5.13 | 5.13 |
| Linux Linux kernel | >=5.7<5.10.37 | |
| Linux Linux kernel | >=5.11<5.11.21 | |
| Linux 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 | ||
| debian/linux | 5.10.223-1 5.10.226-1 6.1.115-1 6.1.119-1 6.11.10-1 6.12.5-1 |
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.
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Reference Links
- https://www.cve.org/CVERecord?id=CVE-2021-31440 https://nvd.nist.gov/vuln/detail/CVE-2021-31440 https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=10bf4e83167cc68595b85fd73bb91e8f2c086e36 https://www.zerodayinitiative.com/blog/2021/5/26/cve-2021-31440-an-incorrect-bounds-calculation-in-the-linux-kernel-ebpf-verifier
- https://bugzilla.redhat.com/show_bug.cgi?id=1964028
- https://access.redhat.com/errata/RHSA-2021:4140
- https://access.redhat.com/errata/RHSA-2021:4356
- https://access.redhat.com/security/cve/cve-2021-31440
- https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=10bf4e83167cc68595b85fd73bb91e8f2c086e36
- https://www.zerodayinitiative.com/advisories/ZDI-21-503/
- https://security.netapp.com/advisory/ntap-20210706-0003/
- https://launchpad.net/bugs/cve/CVE-2021-31440
- https://bugzilla.redhat.com/show_bug.cgi/show_bug.cgi?id=1964029
- https://git.kernel.org/linus/10bf4e83167cc68595b85fd73bb91e8f2c086e36
- https://security-tracker.debian.org/tracker/CVE-2021-31440
- https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2021-31440
- https://nvd.nist.gov/vuln/detail/CVE-2021-31440
- https://ubuntu.com/security/CVE-2021-31440
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