Bug 2464397 (CVE-2026-43038)

Summary:	CVE-2026-43038 kernel: ipv6: icmp: clear skb2->cb[] in ip6_err_gen_icmpv6_unreach()
Product:	[Other] Security Response	Reporter:	OSIDB Bzimport <bzimport>
Component:	vulnerability	Assignee:	Product Security <prodsec-ir-bot>
Status:	NEW ---	QA Contact:
Severity:	high	Docs Contact:
Priority:	high
Version:	unspecified	CC:	rhel-process-autobot, watson-tool-maintainers
Target Milestone:	---	Keywords:	Security
Target Release:	---
Hardware:	All
OS:	Linux
Whiteboard:
Fixed In Version:		Doc Type:	---
Doc Text:	A flaw was found in the Linux kernel's IPv6 ICMP error generation. A remote attacker could send a specially crafted IPv4 ICMP error packet with a Common Internet Protocol Security Option (CIPSO) IP option. This could lead to incorrect handling of packet control block data when generating an IPv6 ICMP error, potentially causing an out-of-bounds memory access. This memory corruption could result in information disclosure or a denial of service.	Story Points:	---
Clone Of:		Environment:
Last Closed:		Type:	---
Regression:	---	Mount Type:	---
Documentation:	---	CRM:
Verified Versions:		Category:	---
oVirt Team:	---	RHEL 7.3 requirements from Atomic Host:
Cloudforms Team:	---	Target Upstream Version:
Embargoed:

Description OSIDB Bzimport 2026-05-01 15:04:29 UTC

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

ipv6: icmp: clear skb2->cb[] in ip6_err_gen_icmpv6_unreach()

Sashiko AI-review observed:

  In ip6_err_gen_icmpv6_unreach(), the skb is an outer IPv4 ICMP error packet
  where its cb contains an IPv4 inet_skb_parm. When skb is cloned into skb2
  and passed to icmp6_send(), it uses IP6CB(skb2).

  IP6CB interprets the IPv4 inet_skb_parm as an inet6_skb_parm. The cipso
  offset in inet_skb_parm.opt directly overlaps with dsthao in inet6_skb_parm
  at offset 18.

  If an attacker sends a forged ICMPv4 error with a CIPSO IP option, dsthao
  would be a non-zero offset. Inside icmp6_send(), mip6_addr_swap() is called
  and uses ipv6_find_tlv(skb, opt->dsthao, IPV6_TLV_HAO).

  This would scan the inner, attacker-controlled IPv6 packet starting at that
  offset, potentially returning a fake TLV without checking if the remaining
  packet length can hold the full 18-byte struct ipv6_destopt_hao.

  Could mip6_addr_swap() then perform a 16-byte swap that extends past the end
  of the packet data into skb_shared_info?

  Should the cb array also be cleared in ip6_err_gen_icmpv6_unreach() and
  ip6ip6_err() to prevent this?

This patch implements the first suggestion.

I am not sure if ip6ip6_err() needs to be changed.
A separate patch would be better anyway.

Comment 1 Keith Grant 2026-05-01 17:54:08 UTC

Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2026050103-CVE-2026-43038-b591@gregkh/T

Comment 4 errata-xmlrpc 2026-06-03 15:19:25 UTC

This issue has been addressed in the following products:

  Red Hat Enterprise Linux 9.2 Update Services for SAP Solutions

Via RHSA-2026:22900 https://access.redhat.com/errata/RHSA-2026:22900

Comment 5 errata-xmlrpc 2026-06-03 19:17:52 UTC

This issue has been addressed in the following products:

  Red Hat Enterprise Linux 9.2 Update Services for SAP Solutions

Via RHSA-2026:22940 https://access.redhat.com/errata/RHSA-2026:22940

Comment 6 errata-xmlrpc 2026-06-04 10:22:43 UTC

This issue has been addressed in the following products:

  Red Hat Enterprise Linux 9.4 Update Services for SAP Solutions

Via RHSA-2026:23237 https://access.redhat.com/errata/RHSA-2026:23237

Comment 7 errata-xmlrpc 2026-06-04 12:16:34 UTC

This issue has been addressed in the following products:

  Red Hat Enterprise Linux 9.6 Extended Update Support

Via RHSA-2026:23224 https://access.redhat.com/errata/RHSA-2026:23224

Comment 8 errata-xmlrpc 2026-06-04 15:45:51 UTC

This issue has been addressed in the following products:

  Red Hat Enterprise Linux 8.8 Update Services for SAP Solutions
  Red Hat Enterprise Linux 8.8 Telecommunications Update Service

Via RHSA-2026:22964 https://access.redhat.com/errata/RHSA-2026:22964

Comment 9 errata-xmlrpc 2026-06-08 03:03:29 UTC

This issue has been addressed in the following products:

  Red Hat Enterprise Linux 10.0 Extended Update Support

Via RHSA-2026:24343 https://access.redhat.com/errata/RHSA-2026:24343

Comment 10 errata-xmlrpc 2026-06-10 20:00:20 UTC

This issue has been addressed in the following products:

  Red Hat Enterprise Linux 8

Via RHSA-2026:25120 https://access.redhat.com/errata/RHSA-2026:25120

Comment 11 errata-xmlrpc 2026-06-10 21:39:04 UTC

This issue has been addressed in the following products:

  Red Hat Enterprise Linux 8

Via RHSA-2026:25121 https://access.redhat.com/errata/RHSA-2026:25121

Comment 12 errata-xmlrpc 2026-06-12 19:51:48 UTC

This issue has been addressed in the following products:

  Red Hat Enterprise Linux 8.6 Extended Update Support Long-Life Add-On
  Red Hat Enterprise Linux 8.6 Advanced Mission Critical Update Support

Via RHSA-2026:25533 https://access.redhat.com/errata/RHSA-2026:25533

Comment 13 errata-xmlrpc 2026-06-17 09:18:44 UTC

This issue has been addressed in the following products:

  Red Hat Enterprise Linux 8.4 Advanced Mission Critical Update Support
  Red Hat Enterprise Linux 8.4 Extended Update Support Long-Life Add-On

Via RHSA-2026:26535 https://access.redhat.com/errata/RHSA-2026:26535