CVE-2026-53263

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.