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VulnerabilityPublished Updated

CVE-2026-43038: Linux kernel · ipv6: icmp: clear skb2->cb[] in ip6_err_gen_icmpv6_unreach()

Affects Linux kernelSource CVE Database V5

0

Not known to be exploited · CVSS 9.8 Critical · fixed in e41953e7d118e2702bcb217879c173d9d1d3cd4e : patch Linux kernel as a priority.

Data as of 26 Oct 2026, 14:18 UTC

CVSS 3.1 base score
9.8Critical
How severe the flaw is on the 0–10 CVSS scale.
EPSS
0.2% chance of exploitation in 30 days – higher than 16% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
CISA SSVC
Exploitation
No evidence of active exploitation and no public proof of concept
Automatable
Attackers can reliably automate steps 1–4 of the kill chain
Technical impact
Total control over the software or total information disclosure

CISA SSVC assessment, 2026-10-16.

Patch
Available – fixed in e41953e7d118e2702bcb217879c173d9d1d3cd4e, c438ba010171b70bad22fc18b1d5bdc3627476e8, a4437faf135da293d16fcc4cc607316742bd0ebb +5
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Exploitation evidence

  1. Disclosed: evidence found.

    CVE published 1 May 2026

  2. Detectable: no evidence on record.

    No public nuclei template indexed

  3. Weaponised: no evidence on record.

    No public exploit code indexed in Metasploit or Exploit-DB

  4. Exploited in the wild: no evidence on record.

    Not in CISA KEV and no source reports exploitation

  5. Observed by OffSeq Mirage: no evidence on record.

    No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 26 Oct 2026.

What to do

Upgrade to a fixed release listed under Affected software.

Affected software

ProductAffectedFixed in
LinuxLinuxAffected
  • ≥ ca15a078bd907df5fc1c009477869c5cbde3b753, < e41953e7d118e2702bcb217879c173d9d1d3cd4e
Fixed in
  • e41953e7d118e2702bcb217879c173d9d1d3cd4e
LinuxLinuxAffected
  • ≥ ca15a078bd907df5fc1c009477869c5cbde3b753, < c438ba010171b70bad22fc18b1d5bdc3627476e8
Fixed in
  • c438ba010171b70bad22fc18b1d5bdc3627476e8
LinuxLinuxAffected
  • ≥ ca15a078bd907df5fc1c009477869c5cbde3b753, < a4437faf135da293d16fcc4cc607316742bd0ebb
Fixed in
  • a4437faf135da293d16fcc4cc607316742bd0ebb
LinuxLinuxAffected
  • ≥ ca15a078bd907df5fc1c009477869c5cbde3b753, < a2edbb6393972a02114b6003953a5cef3104fada
Fixed in
  • a2edbb6393972a02114b6003953a5cef3104fada
LinuxLinuxAffected
  • ≥ ca15a078bd907df5fc1c009477869c5cbde3b753, < 0452b6526b2f54b2413b9cb4ff1ea2ac542c99c7
Fixed in
  • 0452b6526b2f54b2413b9cb4ff1ea2ac542c99c7
LinuxLinuxAffected
  • ≥ ca15a078bd907df5fc1c009477869c5cbde3b753, < 86ab3e55673a7a49a841838776f1ab18d23a67b5
Fixed in
  • 86ab3e55673a7a49a841838776f1ab18d23a67b5

Description

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.

References

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