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).

PUBLISHED Reserved 2026-05-01 | Published 2026-05-01 | Updated 2026-05-03 | Assigner Linux

Product status

References

git.kernel.org/...c/ea9f65b27c8404e164848ebff1443310fd187629

git.kernel.org/...c/d6621f60192fe10c047a4487be42a6f4c150707f

git.kernel.org/...c/2cc6e3b0fe0f0242d1f530a93a4924f48ab85ba5

git.kernel.org/...c/a0c4ce9900a108eaf55d0f3b399cb55999647d39

git.kernel.org/...c/1063515ce15ff31065c4e7f8265f4c2fd3c54876

git.kernel.org/...c/590f622669b97eaf7b57a1de7b0a6e68c5d8b2c3

git.kernel.org/...c/4a622658f384b03560834cbe8ffcfe69a278f7c8

git.kernel.org/...c/2edfa31769a4add828a7e604b21cb82aaaa05925

cve.org (CVE-2026-43037)

nvd.nist.gov (CVE-2026-43037)

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