CVE-2021-4001
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Last Modified:
Insights vulnerability analysis
Description
A race condition was found in the Linux kernel's ebpf verifier between bpf_map_update_elem and bpf_map_freeze due to a missing lock in kernel/bpf/syscall.c. In this flaw, a local user with a special privilege (cap_sys_admin or cap_bpf) can modify the frozen mapped address space.
Statement
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.
Mitigation
Mitigation for this issue is either not available or the currently available options don't meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base, or stability.
Additional information
- Bugzilla 2025645: kernel: race condition when the EBPF map is frozen
- CWE-367: Time-of-check Time-of-use (TOCTOU) Race Condition
- FAQ: Frequently asked questions about CVE-2021-4001
Common Vulnerability Scoring System (CVSS) Score Details
Important note
CVSS scores for open source components depend on vendor-specific factors (e.g. version or build chain). Therefore, Red Hat's score and impact rating can be different from NVD and other vendors. Red Hat remains the authoritative CVE Naming Authority (CNA) source for its products and services (see Red Hat classifications).
The following CVSS metrics and score provided are preliminary and subject to review.
| Red Hat | NVD | |
|---|---|---|
CVSS v3 Base Score | 6.7 | 4.1 |
Attack Vector | Local | Local |
Attack Complexity | Low | High |
Privileges Required | High | High |
User Interaction | None | None |
Scope | Unchanged | Unchanged |
Confidentiality Impact | High | None |
Integrity Impact | High | High |
Availability Impact | High | None |
CVSS v3 Vector
Red Hat: CVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:H
NVD: CVSS:3.1/AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:H/A:N
Acknowledgements
Red Hat would like to thank anciety@starcross, swing@chaitin, and w1tcher@w1tcherSun for reporting this issue.
Frequently Asked Questions
Why is Red Hat's CVSS v3 score or Impact different from other vendors?
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