Frozen-map modification via eBPF update race
Published Jan 21, 2022 · Updated Aug 3, 2024
TOCTOU in the Linux Kernel eBPF verifier before 5.16 rc2 allows local users with CAP_SYS_ADMIN or CAP_BPF to modify frozen maps. The verifier treats a frozen read-only map value as a stable constant while an update started before the freeze can still finish, invalidating its assumptions and enabling out-of-bounds access. Exploitation requires local execution plus CAP_SYS_ADMIN or CAP_BPF; the demonstrated outcome is modification of supposedly immutable map contents.
Summary
What happened
TOCTOU in the Linux Kernel eBPF verifier before 5.16 rc2 allows local users with CAP_SYS_ADMIN or CAP_BPF to modify frozen maps. The verifier treats a frozen read-only map value as a stable constant while an update started before the freeze can still finish, invalidating its assumptions and enabling out-of-bounds access. Exploitation requires local execution plus CAP_SYS_ADMIN or CAP_BPF; the demonstrated outcome is modification of supposedly immutable map contents.
The record
- CVE
- CVE-2021-4001
- Published
- Jan 21, 2022
- Updated
- Aug 3, 2024
- Vendor
- The Linux Kernel Organization
- Product
- Linux Kernel
- Classifications
- CWE-367
- Attack vector
- local
- Privileges
- admin
Timeline
How it unfolded
- Jan 21, 2022CVE publishedPublication date reported by the CVE source.
- Aug 3, 2024Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
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- Affected versionversion=kernel 5.16 rc2
What conditions does exploitation require?
What is affected?
Attacks
What attackers are doing with it
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Weakness, pattern, technique
Public exploit references
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Your stack
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