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Critical severity9.8NVD Advisory· Published May 1, 2026· Updated May 4, 2026

CVE-2026-43037

CVE-2026-43037

Description

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

ip6_tunnel: clear skb2->cb[] in ip4ip6_err()

Oskar Kjos reported the following problem.

ip4ip6_err() calls icmp_send() on a cloned skb whose cb[] was written by the IPv6 receive path as struct inet6_skb_parm. icmp_send() passes IPCB(skb2) to __ip_options_echo(), which interprets that cb[] region as struct inet_skb_parm (IPv4). The layouts differ: inet6_skb_parm.nhoff at offset 14 overlaps inet_skb_parm.opt.rr, producing a non-zero rr value. __ip_options_echo() then reads optlen from attacker-controlled packet data at sptr[rr+1] and copies that many bytes into dopt->__data, a fixed 40-byte stack buffer (IP_OPTIONS_DATA_FIXED_SIZE).

To fix this we clear skb2->cb[], as suggested by Oskar Kjos.

Also add minimal IPv4 header validation (version == 4, ihl >= 5).

Affected products

8
  • Torvalds/Linuxinferred
  • Linux/Kernel7 versions
    cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*+ 6 more
    • cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*range: >=2.6.22,<5.10.253
    • cpe:2.3:o:linux:linux_kernel:7.0:rc1:*:*:*:*:*:*
    • cpe:2.3:o:linux:linux_kernel:7.0:rc2:*:*:*:*:*:*
    • cpe:2.3:o:linux:linux_kernel:7.0:rc3:*:*:*:*:*:*
    • cpe:2.3:o:linux:linux_kernel:7.0:rc4:*:*:*:*:*:*
    • cpe:2.3:o:linux:linux_kernel:7.0:rc5:*:*:*:*:*:*
    • cpe:2.3:o:linux:linux_kernel:7.0:rc6:*:*:*:*:*:*

Patches

0

No patches discovered yet.

Vulnerability mechanics

AI mechanics synthesis has not run for this CVE yet.

News mentions

47