# CVE-2026-99033: net/packet: guard the ll header push in packet_rcv_spkt()


- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Fix available:** Yes
- **Published:** 23 Oct 2026
- **Updated:** 23 Oct 2026
- **Also known as:** AZL-110894, BELL-CVE-2026-99033, DEBIAN-CVE-2026-99033, GHSA-4crx-j28m-6wrf, UBUNTU-CVE-2026-99033

## What is CVE-2026-99033?

CVE-2026-99033 is a vulnerability in Linux, published on 23 Oct 2026. 

### Official description

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

net/packet: guard the ll header push in packet_rcv_spkt()

packet_rcv_spkt() restores the link layer header with

	skb_push(skb, skb->data - skb_mac_header(skb));

That subtraction is only meaningful when the device actually has a link
layer header.  packet_rcv() and tpacket_rcv() both wrap it in
dev_has_header(), which is also the predicate the block comment at the
top of the file states the restore in terms of; packet_rcv_spkt() does
not.  commit d549699048b4 ("net/packet: fix packet receive on L3
devices without visible hard header") introduced the helper and changed
the two call sites, and this one stayed behind.

A device without a visible ll header can leave skb->mac_header at the
0xFFFF sentinel that __alloc_skb() initialises it to.  A CAN skb does:
init_can_skb() sets pkt_type and ip_summed but does not reset the
headers, and commit 9f10374bb024 ("can: remove private CAN skb
headroom infrastructure") dropped the skb_reset_*_header() calls that
used to be there.  skb_mac_header() is then 0xFFFF, the length becomes
a large negative number and skb_push() reports it through
skb_under_panic() -- from softirq context, so it is a full system panic
even with panic_on_oops=0:

  skbuff: skb_under_panic: text:ffffffff8bd21bc1 len:-65455 put:-65471 head:... data:... tail:0x50 end:0x180 dev:can0
  kernel BUG at net/core/skbuff.c:214!
  RIP: 0010:skb_panic+0x50/0x60
  Call Trace:
   <IRQ>
   skb_push+0x38/0x40
   packet_rcv_spkt+0xe1/0x170
   __netif_receive_skb_core.constprop.0+0x7e8/0xd30
   ...
  Kernel panic - not syncing: Fatal exception in interrupt

The socket type is reachable: packet_create() accepts SOCK_PACKET
alongside SOCK_RAW and SOCK_DGRAM behind the same CAP_NET_RAW check,
and neither the socket length nor a capability check keeps it away
from a CAN interface.

The missing skb_reset_*_header() calls in init_can_skb() are a
regression in their own right and are being fixed separately, but a
packet socket should not turn a link layer that did not initialise its
mac header into a kernel panic.  Guard the push the way the other two
receive paths do.

Tested on v7.3-rc5 under QEMU with a slcan device on a pty, which is
the driver RX path: vcan does not reproduce it, because can_send()
resets the headers on the way out.  One SOCK_PACKET socket bound to
can0 and one frame written into the line discipline panics an
unpatched kernel with the trace above; the same image with this patch
prints no panic and powers off normally.  Both kernels are this tree,
defconfig plus CONFIG_CAN_SLCAN=y, differing only in this hunk.

## Which versions are affected by CVE-2026-99033?


## How do I fix CVE-2026-99033?

Upgrade to a fixed version.

## Is CVE-2026-99033 being exploited?

There is no known exploitation of CVE-2026-99033 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-99033 and fix it if it is affected.

What it is: CVE-2026-99033 is a vulnerability in Linux, published on 23 Oct 2026. 
Exploitation: There is no known exploitation of CVE-2026-99033 in the wild and no public exploit code.

Affected product: 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-2026-99033/ (Markdown: https://insights.sbomify.com/CVE-2026-99033/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-99033
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-99033
- OSV: https://osv.dev/vulnerability/CVE-2026-99033

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-99033/
Summaries are generated and may contain mistakes; the official description above is the record.