# CVE-2026-63831: mac802154: llsec: add skb_cow_data() before in-place crypto


- **Severity:** High 8.8 (`CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Fix available:** Yes
- **Published:** 19 Jul 2026
- **Updated:** 19 Oct 2026
- **Also known as:** BELL-CVE-2026-63831, DEBIAN-CVE-2026-63831, GHSA-3745-g9hm-6m5f, ROOT-OS-DEBIAN-11-CVE-2026-63831, ROOT-OS-UBUNTU-2204-CVE-2026-63831, UBUNTU-CVE-2026-63831

## What is CVE-2026-63831?

CVE-2026-63831 is a high-severity vulnerability in Linux kernel, published on 19 Jul 2026. 

### Official description

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

mac802154: llsec: add skb_cow_data() before in-place crypto

llsec_do_encrypt_unauth(), llsec_do_encrypt_auth(),
llsec_do_decrypt_unauth(), and llsec_do_decrypt_auth() all perform
in-place cryptographic transformations on skb data.  They build a
scatterlist with sg_init_one() pointing into the skb's linear data area
and then pass the same scatterlist as both src and dst to the crypto API
(e.g. crypto_skcipher_encrypt/decrypt, crypto_aead_encrypt/decrypt).

On the RX path, __ieee802154_rx_handle_packet() clones the received skb
before handing it to each subscriber via ieee802154_subif_frame().  The
cloned skb shares the same underlying data buffer via reference
counting.  When llsec_do_decrypt() subsequently modifies this shared
buffer in place, it corrupts data that other clones -- potentially
belonging to other sockets or subsystems -- still reference.

On the TX path, similar data sharing can occur when an skb's head has
been cloned (skb_cloned() returns true).

The fix is to call skb_cow_data() before performing any in-place crypto
operation.  skb_cow_data() ensures that the skb's data area is not
shared: if the skb head is cloned or the data spans multiple fragments,
it copies the data into a private buffer that can be safely modified in
place.  This is the same pattern used by:

  - ESP (net/ipv4/esp4.c, net/ipv6/esp6.c)
  - MACsec (drivers/net/macsec.c)
  - WireGuard (drivers/net/wireguard/receive.c)
  - TIPC (net/tipc/crypto.c)

Without this guard, in-place crypto on shared skb data leads to:
  - Silent data corruption of other skb clones
  - Use-after-free when the crypto API scatterwalk writes through a
    page that has already been freed by another clone's kfree_skb()
  - Kernel crashes under concurrent 802.15.4 traffic with security
    enabled (KASAN/KMSAN reports slab-use-after-free)

Found by 0sec (https://0sec.ai) using automated source analysis.

Weakness: CWE-416 (Use After Free)

## Which versions are affected by CVE-2026-63831?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2026-63831?

Upgrade to a fixed version.

## Is CVE-2026-63831 being exploited?

There is no known exploitation of CVE-2026-63831 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-2026-63831 and fix it if it is affected.

What it is: CVE-2026-63831 is a high-severity vulnerability in Linux kernel, published on 19 Jul 2026. 
Exploitation: There is no known exploitation of CVE-2026-63831 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-2026-63831/ (Markdown: https://insights.sbomify.com/CVE-2026-63831/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-63831
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-63831
- OSV: https://osv.dev/vulnerability/CVE-2026-63831

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-63831/
Summaries are generated and may contain mistakes; the official description above is the record.