CVE-2026-43038 ipv6: icmp: clear skb2->cb[] in ip6_err_gen_icmpv6_unreach()
A memory corruption vulnerability in the Linux kernel IPv6 ICMP handling allows attackers to trigger out-of-bounds writes via forged ICMPv4 errors, potentially leading to code execution or system crashes.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-43038?
CVE-2026-43038 is a critical memory corruption vulnerability in Linux kernel, published on 1 May 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official 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.
Which versions are affected by CVE-2026-43038?
It affects 1 product.
Products include Linux kernel.
How do I fix CVE-2026-43038?
Apply the vendor's patch.
Upgrade to the fixed version. Memory-safe languages, compiler hardening and fuzzing prevent most new cases. More about Memory corruption.
Is CVE-2026-43038 being exploited?
There is no known exploitation of CVE-2026-43038 in the wild and no public exploit code.
Other vulnerabilities in Linux kernel
Sources
Also known as BELL-CVE-2026-43038, DEBIAN-CVE-2026-43038, GHSA-78m7-4xgc-xrrq, ROOT-OS-DEBIAN-11-CVE-2026-43038, ROOT-OS-UBUNTU-2204-CVE-2026-43038, ROOT-OS-UBUNTU-2404-CVE-2026-43038 and 1 more.