Bug 2492832 (CVE-2026-53263)

Summary: CVE-2026-53263 kernel: 6lowpan: fix off-by-one in multicast context address compression
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security <prodsec-ir-bot>
Status: NEW --- QA Contact:
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Priority: medium    
Version: unspecifiedCC: rhel-process-autobot, watson-tool-maintainers
Target Milestone: ---Keywords: Security
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Hardware: All   
OS: Linux   
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A flaw was found in the Linux kernel's 6lowpan component. An off-by-one error during multicast context address compression can lead to the transmission of uninitialized kernel stack memory over the network. This vulnerability results in information disclosure, potentially allowing an attacker to access sensitive kernel data.
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Description OSIDB Bzimport 2026-06-25 10:08:06 UTC 
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.
Comment 1 Keith Grant 2026-06-26 01:22:13 UTC 
Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2026062516-CVE-2026-53263-88dd@gregkh/T