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).
Predictions
Heuristic predictions, AS-IS, for prioritization only.
Mitigations
Vendor advisory: debian — https://security-tracker.debian.org/tracker/CVE-2026-43037
Vendor advisory: suse — https://www.suse.com/security/cve/CVE-2026-43037.html
Vendor advisory: 416baaa9-dc9f-4396-8d5f-8c081fb06d67 — https://git.kernel.org/stable/c/ea9f65b27c8404e164848ebff1443310fd187629
Vendor advisory: 416baaa9-dc9f-4396-8d5f-8c081fb06d67 — https://git.kernel.org/stable/c/d6621f60192fe10c047a4487be42a6f4c150707f
Vendor advisory: 416baaa9-dc9f-4396-8d5f-8c081fb06d67 — https://git.kernel.org/stable/c/a0c4ce9900a108eaf55d0f3b399cb55999647d39
Vendor advisory: 416baaa9-dc9f-4396-8d5f-8c081fb06d67 — https://git.kernel.org/stable/c/590f622669b97eaf7b57a1de7b0a6e68c5d8b2c3
Vendor advisory: 416baaa9-dc9f-4396-8d5f-8c081fb06d67 — https://git.kernel.org/stable/c/4a622658f384b03560834cbe8ffcfe69a278f7c8
Vendor advisory: 416baaa9-dc9f-4396-8d5f-8c081fb06d67 — https://git.kernel.org/stable/c/2edfa31769a4add828a7e604b21cb82aaaa05925
Vendor advisory: 416baaa9-dc9f-4396-8d5f-8c081fb06d67 — https://git.kernel.org/stable/c/2cc6e3b0fe0f0242d1f530a93a4924f48ab85ba5
Vendor advisory: 416baaa9-dc9f-4396-8d5f-8c081fb06d67 — https://git.kernel.org/stable/c/1063515ce15ff31065c4e7f8265f4c2fd3c54876
OS impact
| OS | Version | Status | Fixed in |
|---|---|---|---|
| sles | affected | | |
| debian | bookworm | fixed | 6.1.170-1 |
| debian | bullseye | fixed | 6.1.170-1~deb11u1 |
| debian | forky | fixed | 6.19.12-1 |
| debian | sid | fixed | 6.19.12-1 |
| debian | trixie | fixed | 6.12.85-1 |
| linux-kernel | affected | 5.10.253 | |
| linux-kernel | 7.0 | affected | |
Application impact
| Vendor | Product | Versions | Fixed |
|---|---|---|---|
| gcp | | |
References
- https://git.kernel.org/stable/c/1063515ce15ff31065c4e7f8265f4c2fd3c54876
- https://git.kernel.org/stable/c/2cc6e3b0fe0f0242d1f530a93a4924f48ab85ba5
- https://git.kernel.org/stable/c/2edfa31769a4add828a7e604b21cb82aaaa05925
- https://git.kernel.org/stable/c/4a622658f384b03560834cbe8ffcfe69a278f7c8
- https://git.kernel.org/stable/c/590f622669b97eaf7b57a1de7b0a6e68c5d8b2c3
- https://git.kernel.org/stable/c/a0c4ce9900a108eaf55d0f3b399cb55999647d39
- https://git.kernel.org/stable/c/d6621f60192fe10c047a4487be42a6f4c150707f
- https://git.kernel.org/stable/c/ea9f65b27c8404e164848ebff1443310fd187629
- https://www.suse.com/security/cve/CVE-2026-43037.html
- https://security-tracker.debian.org/tracker/CVE-2026-43037
CWEs
CWE-787
Verify integrity in audit chain (admin only). AS-IS.