# CVE-2024-26636: llc: make llc_ui_sendmsg() more robust against bonding changes

> A race condition in the Linux kernel LLC module allows local attackers to trigger a kernel panic via improper socket lock handling during bonding changes.

- **Severity:** Medium 5.5 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 18 Mar 2024
- **Updated:** 11 May 2026
- **Also known as:** BELL-CVE-2024-26636, DEBIAN-CVE-2024-26636, GHSA-33v3-2qxj-vgv5, UBUNTU-CVE-2024-26636

## What is CVE-2024-26636?

CVE-2024-26636 is a medium-severity vulnerability in Debian Debian Linux, published on 18 Mar 2024. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

In the Linux kernel, the following vulnerability has been resolved:

llc: make llc_ui_sendmsg() more robust against bonding changes

syzbot was able to trick llc_ui_sendmsg(), allocating an skb with no
headroom, but subsequently trying to push 14 bytes of Ethernet header [1]

Like some others, llc_ui_sendmsg() releases the socket lock before
calling sock_alloc_send_skb().
Then it acquires it again, but does not redo all the sanity checks
that were performed.

This fix:

- Uses LL_RESERVED_SPACE() to reserve space.
- Check all conditions again after socket lock is held again.
- Do not account Ethernet header for mtu limitation.

[1]

skbuff: skb_under_panic: text:ffff800088baa334 len:1514 put:14 head:ffff0000c9c37000 data:ffff0000c9c36ff2 tail:0x5dc end:0x6c0 dev:bond0

 kernel BUG at net/core/skbuff.c:193 !
Internal error: Oops - BUG: 00000000f2000800 [#1] PREEMPT SMP
Modules linked in:
CPU: 0 PID: 6875 Comm: syz-executor.0 Not tainted 6.7.0-rc8-syzkaller-00101-g0802e17d9aca-dirty #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 11/17/2023
pstate: 60400005 (nZCv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--)
 pc : skb_panic net/core/skbuff.c:189 [inline]
 pc : skb_under_panic+0x13c/0x140 net/core/skbuff.c:203
 lr : skb_panic net/core/skbuff.c:189 [inline]
 lr : skb_under_panic+0x13c/0x140 net/core/skbuff.c:203
sp : ffff800096f97000
x29: ffff800096f97010 x28: ffff80008cc8d668 x27: dfff800000000000
x26: ffff0000cb970c90 x25: 00000000000005dc x24: ffff0000c9c36ff2
x23: ffff0000c9c37000 x22: 00000000000005ea x21: 00000000000006c0
x20: 000000000000000e x19: ffff800088baa334 x18: 1fffe000368261ce
x17: ffff80008e4ed000 x16: ffff80008a8310f8 x15: 0000000000000001
x14: 1ffff00012df2d58 x13: 0000000000000000 x12: 0000000000000000
x11: 0000000000000001 x10: 0000000000ff0100 x9 : e28a51f1087e8400
x8 : e28a51f1087e8400 x7 : ffff80008028f8d0 x6 : 0000000000000000
x5 : 0000000000000001 x4 : 0000000000000001 x3 : ffff800082b78714
x2 : 0000000000000001 x1 : 0000000100000000 x0 : 0000000000000089
Call trace:
  skb_panic net/core/skbuff.c:189 [inline]
  skb_under_panic+0x13c/0x140 net/core/skbuff.c:203
  skb_push+0xf0/0x108 net/core/skbuff.c:2451
  eth_header+0x44/0x1f8 net/ethernet/eth.c:83
  dev_hard_header include/linux/netdevice.h:3188 [inline]
  llc_mac_hdr_init+0x110/0x17c net/llc/llc_output.c:33
  llc_sap_action_send_xid_c+0x170/0x344 net/llc/llc_s_ac.c:85
  llc_exec_sap_trans_actions net/llc/llc_sap.c:153 [inline]
  llc_sap_next_state net/llc/llc_sap.c:182 [inline]
  llc_sap_state_process+0x1ec/0x774 net/llc/llc_sap.c:209
  llc_build_and_send_xid_pkt+0x12c/0x1c0 net/llc/llc_sap.c:270
  llc_ui_sendmsg+0x7bc/0xb1c net/llc/af_llc.c:997
  sock_sendmsg_nosec net/socket.c:730 [inline]
  __sock_sendmsg net/socket.c:745 [inline]
  sock_sendmsg+0x194/0x274 net/socket.c:767
  splice_to_socket+0x7cc/0xd58 fs/splice.c:881
  do_splice_from fs/splice.c:933 [inline]
  direct_splice_actor+0xe4/0x1c0 fs/splice.c:1142
  splice_direct_to_actor+0x2a0/0x7e4 fs/splice.c:1088
  do_splice_direct+0x20c/0x348 fs/splice.c:1194
  do_sendfile+0x4bc/0xc70 fs/read_write.c:1254
  __do_sys_sendfile64 fs/read_write.c:1322 [inline]
  __se_sys_sendfile64 fs/read_write.c:1308 [inline]
  __arm64_sys_sendfile64+0x160/0x3b4 fs/read_write.c:1308
  __invoke_syscall arch/arm64/kernel/syscall.c:37 [inline]
  invoke_syscall+0x98/0x2b8 arch/arm64/kernel/syscall.c:51
  el0_svc_common+0x130/0x23c arch/arm64/kernel/syscall.c:136
  do_el0_svc+0x48/0x58 arch/arm64/kernel/syscall.c:155
  el0_svc+0x54/0x158 arch/arm64/kernel/entry-common.c:678
  el0t_64_sync_handler+0x84/0xfc arch/arm64/kernel/entry-common.c:696
  el0t_64_sync+0x190/0x194 arch/arm64/kernel/entry.S:595
Code: aa1803e6 aa1903e7 a90023f5 94792f6a (d4210000)

## Which versions are affected by CVE-2024-26636?

It affects 2 products.


Products: Debian Debian Linux, Linux kernel.

## How do I fix CVE-2024-26636?

Apply the vendor's patch.

## Is CVE-2024-26636 being exploited?

There is no known exploitation of CVE-2024-26636 in the wild and no public exploit code.

## Other vulnerabilities in Debian Debian Linux

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- [CVE-2026-24061](https://insights.sbomify.com/CVE-2026-24061/): GNU InetUtils Argument Injection (critical 9.8, exploited in the wild)
- [CVE-2025-39682](https://insights.sbomify.com/CVE-2025-39682/): Linux Kernel Improper Check for Unusual or Exceptional Conditions (critical 9.8, exploited in the wild)
- [CVE-2024-9680](https://insights.sbomify.com/CVE-2024-9680/): Mozilla Firefox Use-After-Free (critical 9.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2024-26636 and fix it if it is affected.

What it is: CVE-2024-26636 is a medium-severity vulnerability in Debian Debian Linux, published on 18 Mar 2024. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2024-26636 in the wild and no public exploit code.

Affected product: Debian Debian Linux. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2024-26636/ (Markdown: https://insights.sbomify.com/CVE-2024-26636/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2024-26636
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2024-26636
- OSV: https://osv.dev/vulnerability/CVE-2024-26636

---
From sbomify Insights: https://insights.sbomify.com/CVE-2024-26636/
Summaries are generated and may contain mistakes; the official description above is the record.