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

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Summary

CVECVE-2026-43037
StatePUBLISHED
AssignerLinux
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-05-01 15:16:48 UTC
Updated2026-05-03 07:16:23 UTC
DescriptionIn 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).

Risk And Classification

Primary CVSS: v3.1 9.8 CRITICAL from 416baaa9-dc9f-4396-8d5f-8c081fb06d67

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

EPSS: 0.000240000 probability, percentile 0.068220000 (date 2026-05-02)

VersionSourceTypeScoreSeverityVector
3.1416baaa9-dc9f-4396-8d5f-8c081fb06d67Secondary9.8CRITICALCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
3.1CNADECLARED9.8CRITICALCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

CVSS v3.1 Breakdown

Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Linux Linux affected c4d3efafcc933fd2ffd169d7dc4f980393a13796 ea9f65b27c8404e164848ebff1443310fd187629 git Not specified
CNA Linux Linux affected c4d3efafcc933fd2ffd169d7dc4f980393a13796 d6621f60192fe10c047a4487be42a6f4c150707f git Not specified
CNA Linux Linux affected c4d3efafcc933fd2ffd169d7dc4f980393a13796 2cc6e3b0fe0f0242d1f530a93a4924f48ab85ba5 git Not specified
CNA Linux Linux affected c4d3efafcc933fd2ffd169d7dc4f980393a13796 a0c4ce9900a108eaf55d0f3b399cb55999647d39 git Not specified
CNA Linux Linux affected c4d3efafcc933fd2ffd169d7dc4f980393a13796 1063515ce15ff31065c4e7f8265f4c2fd3c54876 git Not specified
CNA Linux Linux affected c4d3efafcc933fd2ffd169d7dc4f980393a13796 590f622669b97eaf7b57a1de7b0a6e68c5d8b2c3 git Not specified
CNA Linux Linux affected c4d3efafcc933fd2ffd169d7dc4f980393a13796 4a622658f384b03560834cbe8ffcfe69a278f7c8 git Not specified
CNA Linux Linux affected c4d3efafcc933fd2ffd169d7dc4f980393a13796 2edfa31769a4add828a7e604b21cb82aaaa05925 git Not specified
CNA Linux Linux affected 2.6.22 Not specified
CNA Linux Linux unaffected 2.6.22 semver Not specified
CNA Linux Linux unaffected 5.10.253 5.10.* semver Not specified
CNA Linux Linux unaffected 5.15.203 5.15.* semver Not specified
CNA Linux Linux unaffected 6.1.168 6.1.* semver Not specified
CNA Linux Linux unaffected 6.6.134 6.6.* semver Not specified
CNA Linux Linux unaffected 6.12.81 6.12.* semver Not specified
CNA Linux Linux unaffected 6.18.22 6.18.* semver Not specified
CNA Linux Linux unaffected 6.19.12 6.19.* semver Not specified
CNA Linux Linux unaffected 7.0 * original_commit_for_fix Not specified

References

ReferenceSourceLinkTags
git.kernel.org/stable/c/2edfa31769a4add828a7e604b21cb82aaaa05925 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/1063515ce15ff31065c4e7f8265f4c2fd3c54876 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/a0c4ce9900a108eaf55d0f3b399cb55999647d39 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/d6621f60192fe10c047a4487be42a6f4c150707f 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/590f622669b97eaf7b57a1de7b0a6e68c5d8b2c3 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/ea9f65b27c8404e164848ebff1443310fd187629 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/2cc6e3b0fe0f0242d1f530a93a4924f48ab85ba5 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/4a622658f384b03560834cbe8ffcfe69a278f7c8 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
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