# CVE-2026-45842: slip: reject VJ receive packets on instances with no rstate array

> An attacker with CAP_NET_ADMIN can trigger a kernel crash via a null pointer dereference in the SLIP driver when processing VJ compressed packets.

- **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:** 27 May 2026
- **Updated:** 15 Oct 2026
- **Also known as:** AZL-88490, BELL-CVE-2026-45842, DEBIAN-CVE-2026-45842, GHSA-g2vj-v28f-r7cf, ROOT-OS-DEBIAN-11-CVE-2026-45842, ROOT-OS-DEBIAN-12-CVE-2026-45842, ROOT-OS-DEBIAN-13-CVE-2026-45842, ROOT-OS-UBUNTU-2204-CVE-2026-45842, ROOT-OS-UBUNTU-2404-CVE-2026-45842, UBUNTU-CVE-2026-45842

## What is CVE-2026-45842?

CVE-2026-45842 is a medium-severity vulnerability in Linux kernel, published on 27 May 2026. 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:

slip: reject VJ receive packets on instances with no rstate array

slhc_init() accepts rslots == 0 as a valid configuration, with the
documented meaning of 'no receive compression'. In that case the
allocation loop in slhc_init() is skipped, so comp->rstate stays
NULL and comp->rslot_limit stays 0 (from the kzalloc of struct
slcompress).

The receive helpers do not defend against that configuration.
slhc_uncompress() dereferences comp->rstate[x] when the VJ header
carries an explicit connection ID, and slhc_remember() later assigns
cs = &comp->rstate[...] after only comparing the packet's slot number
to comp->rslot_limit. Because rslot_limit is 0, slot 0 passes the
range check, and the code dereferences a NULL rstate.

The configuration is reachable in-tree through PPP. PPPIOCSMAXCID
stores its argument in a signed int, and (val >> 16) uses arithmetic
shift. Passing 0xffff0000 therefore sign-extends to -1, so val2 + 1
is 0 and ppp_generic.c ends up calling slhc_init(0, 1). Because
/dev/ppp open is gated by ns_capable(CAP_NET_ADMIN), the whole path
is reachable from an unprivileged user namespace. Once the malformed
VJ state is installed, any inbound VJ-compressed or VJ-uncompressed
frame that selects slot 0 crashes the kernel in softirq context:

 Oops: general protection fault, probably for non-canonical
       address 0xdffffc0000000000: 0000 [#1] SMP KASAN NOPTI
 KASAN: null-ptr-deref in range [0x0000000000000000-0x0000000000000007]
 RIP: 0010:slhc_uncompress (drivers/net/slip/slhc.c:519)
 Call Trace:
  <TASK>
  ppp_receive_nonmp_frame (drivers/net/ppp/ppp_generic.c:2466)
  ppp_input (drivers/net/ppp/ppp_generic.c:2359)
  ppp_async_process (drivers/net/ppp/ppp_async.c:492)
  tasklet_action_common (kernel/softirq.c:926)
  handle_softirqs (kernel/softirq.c:623)
  run_ksoftirqd (kernel/softirq.c:1055)
  smpboot_thread_fn (kernel/smpboot.c:160)
  kthread (kernel/kthread.c:436)
  ret_from_fork (arch/x86/kernel/process.c:164)
  </TASK>

Reject the receive side on such instances instead of touching rstate.
slhc_uncompress() falls through to its existing 'bad' label, which
bumps sls_i_error and enters the toss state. slhc_remember() mirrors
that with an explicit sls_i_error increment followed by slhc_toss();
the sls_i_runt counter is not used here because a missing rstate is
an internal configuration state, not a runt packet.

The transmit path is unaffected: the only in-tree caller that picks
rslots from userspace (ppp_generic.c) still supplies tslots >= 1, and
slip.c always calls slhc_init(16, 16), so comp->tstate remains valid
and slhc_compress() continues to work.

Weakness: CWE-476 (NULL Pointer Dereference)

## Which versions are affected by CVE-2026-45842?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2026-45842?

Apply the vendor's patch.

## Is CVE-2026-45842 being exploited?

There is no known exploitation of CVE-2026-45842 in the wild and no public exploit code.

## Other vulnerabilities in Linux kernel

- [CVE-2026-53266](https://insights.sbomify.com/CVE-2026-53266/): Linux Kernel Out-of-Bounds Write (high 8.8, exploited in the wild)
- [CVE-2013-6282](https://insights.sbomify.com/CVE-2013-6282/): Linux Kernel Improper Input Validation (high 8.8, exploited in the wild)
- [CVE-2022-0185](https://insights.sbomify.com/CVE-2022-0185/): Linux Kernel Heap-Based Buffer Overflow (high 8.4, exploited in the wild)
- [CVE-2013-2094](https://insights.sbomify.com/CVE-2013-2094/): Linux Kernel Privilege Escalation (high 8.4, exploited in the wild)
- [CVE-2026-53362](https://insights.sbomify.com/CVE-2026-53362/): Linux Kernel Unspecified (high 7.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-45842 and fix it if it is affected.

What it is: CVE-2026-45842 is a medium-severity vulnerability in Linux kernel, published on 27 May 2026. 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-2026-45842 in the wild and no public exploit code.

Affected product: Linux kernel. 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-2026-45842/ (Markdown: https://insights.sbomify.com/CVE-2026-45842/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-45842
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-45842
- OSV: https://osv.dev/vulnerability/CVE-2026-45842

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-45842/
Summaries are generated and may contain mistakes; the official description above is the record.