medium
5.5
CWE
125 863
Advisory Published
CVE Published
Updated

CVE-2021-29155

First published: Sun Apr 18 2021(Updated: )

A vulnerability was discovered in retrieve_ptr_limit in kernel/bpf/verifier.c in the Linux kernel mechanism to mitigate speculatively out-of-bounds loads (Spectre mitigation). In this flaw a local, special user privileged (CAP_SYS_ADMIN) BPF program running on affected systems may bypass the protection, and execute speculatively out-of-bounds loads from the kernel memory. This can be abused to extract contents of kernel memory via side-channel.

Credit: cve@mitre.org cve@mitre.org cve@mitre.org

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<5.12
5.12
Linux kernel<5.11.16
Fedora=32
Fedora=33
Fedora=34
Debian=9.0
debian/linux
5.10.223-1
5.10.234-1
6.1.123-1
6.1.128-1
6.12.12-1
6.12.16-1

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://www.openwall.com/lists/oss-security/2021/04/18/4

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Reference Links

Parent vulnerabilities

(Appears in the following advisories)

Frequently Asked Questions

  • What is the severity of CVE-2021-29155?

    The severity of CVE-2021-29155 is categorized as critical due to its potential to allow local attackers to bypass security mechanisms.

  • How do I fix CVE-2021-29155?

    To fix CVE-2021-29155, update your Linux kernel to the latest version as specified in the security advisories.

  • What systems are affected by CVE-2021-29155?

    CVE-2021-29155 affects various versions of the Linux kernel, particularly those prior to version 5.12 and specific Red Hat kernel packages.

  • What is the exploitability of CVE-2021-29155?

    CVE-2021-29155 is exploitable by local users with special privileges, which may lead to unauthorized access or manipulation of system memory.

  • Is CVE-2021-29155 related to Spectre vulnerabilities?

    Yes, CVE-2021-29155 is a vulnerability that pertains to the Linux kernel's mechanism designed to mitigate Spectre-related issues.

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