VULNERABILITY INTELLIGENCE

CVE-2026-43037

CVSS score9.8 CRITICAL
EPSS probability0.69%
CISA KEVNot currently listed
Published2026-05-01
Last modified2026-10-19
CVSS vectorCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

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).

Weakness classification

  • nvd@nist.gov: CWE-787
  • 134c704f-9b21-4f2e-91b3-4a467353bcc0: CWE-121
  • 0b0ca135-0b70-47e7-9f44-1890c2a1c46c: CWE-843

Primary references