What’s Vulnerable › Vulnerabilities
CVE-2021-3490: Linux kernel eBPF bitwise ops ALU32 bounds tracking
- Severity: high (CVSS 7.8 v3.1)
- Exploited in the wild: not listed in CISA KEV
- EPSS: 27.4% probability of exploitation in the next 30 days
- Public exploit or detection template: yes
- Published: 2021-06-04 · updated 2026-06-17
- Weakness: CWE-20
Description
The eBPF ALU32 bounds tracking for bitwise ops (AND, OR and XOR) in the Linux kernel did not properly update 32-bit bounds, which could be turned into out of bounds reads and writes in the Linux kernel and therefore, arbitrary code execution. This issue was fixed via commit 049c4e13714e ("bpf: Fix alu32 const subreg bound tracking on bitwise operations") (v5.13-rc4) and backported to the stable kernels in v5.12.4, v5.11.21, and v5.10.37. The AND/OR issues were introduced by commit 3f50f132d840 ("bpf: Verifier, do explicit ALU32 bounds tracking") (5.7-rc1) and the XOR variant was introduced by 2921c90d4718 ("bpf:Fix a verifier failure with xor") ( 5.10-rc1).
Affected products
- Canonical Ubuntu Linux: 20.04, 20.10, 21.04
- Linux kernel: from 5.10 before 5.10.37; from 5.11 before 5.11.21; from 5.12 before 5.12.4; 5.13, 5.13-rc1, 5.13-rc2, 5.13-rc3 — fixed in 5.10.37, 5.11.21, 5.12.4
How to fix
Upgrade to a fixed version: Linux kernel 5.10.37, 5.11.21, 5.12.4. Check the vendor advisory for mitigations.
References
- http://packetstormsecurity.com/files/164015/Linux-eBPF-ALU32-32-bit-Invalid-Bounds-Tracking-Local-Privilege-Escalation.html
- https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf.git/commit/?id=049c4e13714ecbca567b4d5f6d563f05d431c80e
- https://security.netapp.com/advisory/ntap-20210716-0004/
- https://ubuntu.com/security/notices/USN-4949-1
- https://ubuntu.com/security/notices/USN-4950-1
- https://www.openwall.com/lists/oss-security/2021/05/11/11
- https://www.zerodayinitiative.com/advisories/ZDI-21-606/
- http://packetstormsecurity.com/files/164015/Linux-eBPF-ALU32-32-bit-Invalid-Bounds-Tracking-Local-Privilege-Escalation.html
- https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf.git/commit/?id=049c4e13714ecbca567b4d5f6d563f05d431c80e
- https://security.netapp.com/advisory/ntap-20210716-0004/
- https://ubuntu.com/security/notices/USN-4949-1
- https://ubuntu.com/security/notices/USN-4950-1
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