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Critical 9.8Published May 1, 2026

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

Updated under an hour ago ()

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It affects Linux and 12 other products. Add what you run to find out whether that includes you.

No exploitation reported and no EPSS estimate yet.

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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).

CVSS
9.8 CRITICAL (v3.1, CNA)CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Weakness (CWE)
CWE-843, CWE-121
Known exploited
Not in CISA's KEV catalog
EPSS (exploitation in the next 30 days)
Not loaded for this CVE
Assigned by
Linux
NVD analysis
Modified
Record last updated
Oct 19, 2026
First seen by InfoSec Signals
Oct 9, 2026

Affected products

Affected products
Linux Linux
linux:linux (from the name)
from c4d3efafcc933fd2ffd169d7dc4f980393a13796 before ea9f65b27c8404e164848ebff1443310fd187629; from c4d3efafcc933fd2ffd169d7dc4f980393a13796 before d6621f60192fe10c047a4487be42a6f4c150707f; from c4d3efafcc933fd2ffd169d7dc4f980393a13796 before 2cc6e3b0fe0f0242d1f530a93a4924f48ab85ba5; from c4d3efafcc933fd2ffd169d7dc4f980393a13796 before a0c4ce9900a108eaf55d0f3b399cb55999647d39; from c4d3efafcc933fd2ffd169d7dc4f980393a13796 before 1063515ce15ff31065c4e7f8265f4c2fd3c54876; from c4d3efafcc933fd2ffd169d7dc4f980393a13796 before 590f622669b97eaf7b57a1de7b0a6e68c5d8b2c3; from c4d3efafcc933fd2ffd169d7dc4f980393a13796 before 4a622658f384b03560834cbe8ffcfe69a278f7c8; from c4d3efafcc933fd2ffd169d7dc4f980393a13796 before 2edfa31769a4add828a7e604b21cb82aaaa05925
CNA record
Red Hat NVIDIA for RHEL 10
redhat:enterprise_linux_nvidia
from 0:6.12.0-212.10.el10nv not affected; from 0:6.12.0-231.12.el10nv not affected
CISA ADP
from 0:6.12.0-211.22.1.el10_2 not affected
CISA ADP
from 0:6.12.0-55.77.1.el10_0 not affected
CISA ADP
from 0:2.6.32-754.61.1.el6 not affected
CISA ADP
from 0:3.10.0-1160.155.1.rt56.1307.el7 not affected
CISA ADP
from 0:4.18.0-305.194.1.el8_4 not affected
CISA ADP
from 0:4.18.0-305.194.1.el8_4 not affected
CISA ADP
from 0:4.18.0-477.145.1.el8_8 not affected
CISA ADP
from 0:4.18.0-477.145.1.el8_8 not affected
CISA ADP

References

References

The CVE record is authoritative. Products marked “from the name” were identified from the CNA's free-text names, not a CPE, and are matched less certainly. This product uses the NVD API but is not endorsed or certified by the NVD.

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