# CVE-2021-4001: linux: A race condition was found in the Linux kernel's ebpf verifier between bpf_map_update_elem and bpf_map_freeze due to...

CVE-2021-4001 is fixed in linux on 1 platform, first by DEBIAN-CVE-2021-4001, released January 21, 2022. It is not reported as exploited. Patch Radar priority: Routine.

- Web page: https://patchblox.com/security/cve/CVE-2021-4001
- Priority: Routine
- CVSS: 4.1 (medium)
- EPSS: 0.0019
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Jan 21, 2022

## 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. This flaw affects kernel versions prior to 5.16 rc2.

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | linux Debian 12.15 (bookworm) | 5.15.5-1 | [DEBIAN-CVE-2021-4001](https://patchblox.com/security/data/fix/linux/debian-cve-2021-4001.md) | Jan 21, 2022 |
| Linux | linux Debian 13.5 (trixie) | 5.15.5-1 | [DEBIAN-CVE-2021-4001](https://patchblox.com/security/data/fix/linux/debian-cve-2021-4001.md) | Jan 21, 2022 |
| Linux | linux Debian 14 | 5.15.5-1 | [DEBIAN-CVE-2021-4001](https://patchblox.com/security/data/fix/linux/debian-cve-2021-4001.md) | Jan 21, 2022 |

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Data as of 2026-11-09T01:18:40Z UTC. Source: Patchblox Patch Radar (https://patchblox.com/security/patch-radar). Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo

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