CVE-2026-43037
ip6_tunnel: clear skb2->cb[] in ip4ip6_err()
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).
INFO
Published Date :
May 1, 2026, 3:16 p.m.
Last Modified :
May 1, 2026, 3:24 p.m.
Remotely Exploit :
No
Source :
416baaa9-dc9f-4396-8d5f-8c081fb06d67
Affected Products
The following products are affected by CVE-2026-43037
vulnerability.
Even if cvefeed.io is aware of the exact versions of the
products
that
are
affected, the information is not represented in the table below.
No affected product recoded yet
Solution
- Update the Linux kernel to the latest version.
- Verify kernel version after applying updates.
- Review system logs for related errors.
References to Advisories, Solutions, and Tools
Here, you will find a curated list of external links that provide in-depth
information, practical solutions, and valuable tools related to
CVE-2026-43037.
CWE - Common Weakness Enumeration
While CVE identifies
specific instances of vulnerabilities, CWE categorizes the common flaws or
weaknesses that can lead to vulnerabilities. CVE-2026-43037 is
associated with the following CWEs:
Common Attack Pattern Enumeration and Classification (CAPEC)
Common Attack Pattern Enumeration and Classification
(CAPEC)
stores attack patterns, which are descriptions of the common attributes and
approaches employed by adversaries to exploit the CVE-2026-43037
weaknesses.
We scan GitHub repositories to detect new proof-of-concept exploits. Following list is a collection of public exploits and proof-of-concepts, which have been published on GitHub (sorted by the most recently updated).
Results are limited to the first 15 repositories due to potential performance issues.
The following list is the news that have been mention
CVE-2026-43037 vulnerability anywhere in the article.
The following table lists the changes that have been made to the
CVE-2026-43037 vulnerability over time.
Vulnerability history details can be useful for understanding the evolution of a vulnerability, and for identifying the most recent changes that may impact the vulnerability's severity, exploitability, or other characteristics.
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New CVE Received by 416baaa9-dc9f-4396-8d5f-8c081fb06d67
May. 01, 2026
Action Type Old Value New Value Added 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). Added Reference https://git.kernel.org/stable/c/1063515ce15ff31065c4e7f8265f4c2fd3c54876 Added Reference https://git.kernel.org/stable/c/2cc6e3b0fe0f0242d1f530a93a4924f48ab85ba5 Added Reference https://git.kernel.org/stable/c/2edfa31769a4add828a7e604b21cb82aaaa05925 Added Reference https://git.kernel.org/stable/c/4a622658f384b03560834cbe8ffcfe69a278f7c8 Added Reference https://git.kernel.org/stable/c/590f622669b97eaf7b57a1de7b0a6e68c5d8b2c3 Added Reference https://git.kernel.org/stable/c/a0c4ce9900a108eaf55d0f3b399cb55999647d39 Added Reference https://git.kernel.org/stable/c/d6621f60192fe10c047a4487be42a6f4c150707f Added Reference https://git.kernel.org/stable/c/ea9f65b27c8404e164848ebff1443310fd187629