CVE-2026-43037 — ip6_tunnel: clear skb2->cb[] in ip4ip6_err()

Description (CNA)

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 (CNA)

Vendor / product	Versions
Linux / Linux	affected c4d3efafcc933fd2ffd169d7dc4f980393a13796 before ea9f65b27c8404e164848ebff1443310fd187629; affected c4d3efafcc933fd2ffd169d7dc4f980393a13796 before d6621f60192fe10c047a4487be42a6f4c150707f; affected c4d3efafcc933fd2ffd169d7dc4f980393a13796 before 2cc6e3b0fe0f0242d1f530a93a4924f48ab85ba5; affected c4d3efafcc933fd2ffd169d7dc4f980393a13796 before a0c4ce9900a108eaf55d0f3b399cb55999647d39; affected c4d3efafcc933fd2ffd169d7dc4f980393a13796 before 1063515ce15ff31065c4e7f8265f4c2fd3c54876; affected c4d3efafcc933fd2ffd169d7dc4f980393a13796 before 590f622669b97eaf7b57a1de7b0a6e68c5d8b2c3; affected c4d3efafcc933fd2ffd169d7dc4f980393a13796 before 4a622658f384b03560834cbe8ffcfe69a278f7c8; affected c4d3efafcc933fd2ffd169d7dc4f980393a13796 before 2edfa31769a4add828a7e604b21cb82aaaa05925
Linux / Linux	affected 2.6.22; unaffected 0 before 2.6.22; unaffected 5.10.253 through 5.10.; unaffected 5.15.203 through 5.15.; unaffected 6.1.168 through 6.1.; unaffected 6.6.134 through 6.6.; unaffected 6.12.81 through 6.12.; unaffected 6.18.22 through 6.18.; unaffected 6.19.12 through 6.19.; unaffected 7.0 through

Vendor / product

Versions

Linux / Linux

affected c4d3efafcc933fd2ffd169d7dc4f980393a13796 before ea9f65b27c8404e164848ebff1443310fd187629; affected c4d3efafcc933fd2ffd169d7dc4f980393a13796 before d6621f60192fe10c047a4487be42a6f4c150707f; affected c4d3efafcc933fd2ffd169d7dc4f980393a13796 before 2cc6e3b0fe0f0242d1f530a93a4924f48ab85ba5; affected c4d3efafcc933fd2ffd169d7dc4f980393a13796 before a0c4ce9900a108eaf55d0f3b399cb55999647d39; affected c4d3efafcc933fd2ffd169d7dc4f980393a13796 before 1063515ce15ff31065c4e7f8265f4c2fd3c54876; affected c4d3efafcc933fd2ffd169d7dc4f980393a13796 before 590f622669b97eaf7b57a1de7b0a6e68c5d8b2c3; affected c4d3efafcc933fd2ffd169d7dc4f980393a13796 before 4a622658f384b03560834cbe8ffcfe69a278f7c8; affected c4d3efafcc933fd2ffd169d7dc4f980393a13796 before 2edfa31769a4add828a7e604b21cb82aaaa05925

Linux / Linux

affected 2.6.22; unaffected 0 before 2.6.22; unaffected 5.10.253 through 5.10.*; unaffected 5.15.203 through 5.15.*; unaffected 6.1.168 through 6.1.*; unaffected 6.6.134 through 6.6.*; unaffected 6.12.81 through 6.12.*; unaffected 6.18.22 through 6.18.*; unaffected 6.19.12 through 6.19.*; unaffected 7.0 through *

CWE

No CWE identifiers supplied.

References

ADP enrichment

redhat-SADP

A flaw was found in the Linux kernel's IPv6 tunnel implementation. A remote attacker could exploit this flaw by sending malicious ICMPv6 error messages to cause a stack-based buffer overflow in the kernel's IPv4-over-IPv6 tunnel error handling code. This could result in a kernel crash (denial of service) or potentially allow arbitrary code execution with kernel privileges.

CISA-ADP

No English description supplied.

No references supplied.