Linux Kernel: IPv6/IPv4 Tunnel Bug Enables Buffer Overwrite
CVE-2026-43037 Published on May 1, 2026

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

NVD

Vulnerability Analysis

CVE-2026-43037 can be exploited with network access, and requires small amount of user privileges. This vulnerability is considered to have a low attack complexity. The potential impact of an exploit of this vulnerability is considered to be very high.

Attack Vector:
NETWORK
Attack Complexity:
LOW
Privileges Required:
LOW
User Interaction:
NONE
Scope:
UNCHANGED
Confidentiality Impact:
HIGH
Integrity Impact:
HIGH
Availability Impact:
HIGH

Weakness Type

What is an Object Type Confusion Vulnerability?

The program allocates or initializes a resource such as a pointer, object, or variable using one type, but it later accesses that resource using a type that is incompatible with the original type.

CVE-2026-43037 has been classified to as an Object Type Confusion vulnerability or weakness.


Products Associated with CVE-2026-43037

You can be notified by email with stack.watch whenever vulnerabilities like CVE-2026-43037 are published in these products:

Linux Kernel
 
Red Hat Enterprise Linux Nvidia
 
Red Hat Rhel Els
 
Red Hat Openshift
 
Red Hat Enterprise Linux Eus
 
Red Hat Enterprise Linux (RHEL)
 
Red Hat Rhel E4s
 
Red Hat Rhel Eus
 
Red Hat Rhel Aus
 
Red Hat Rhel Eus Long Life
 
Red Hat Rhel Tus
 

Affected Versions

Linux: Linux: Red Hat NVIDIA for RHEL 10: Red Hat Enterprise Linux Server -EXTENSION(v. 6 ELS-EXTENSION): Red Hat Enterprise Linux Server Optional -EXTENSION (v. 6 ELS -EXTENSION): Red Hat Enterprise Linux Server (v. 7 ELS): Red Hat Enterprise Linux Server Optional (v. 7 ELS): Red Hat OpenShift Container Platform 4.12: Red Hat OpenShift Container Platform 4.13: Red Hat OpenShift Container Platform 4.18: Red Hat OpenShift Container Platform 4.19: Red Hat OpenShift Container Platform 4.20: Red Hat OpenShift Container Platform 4.21: Red Hat Enterprise Linux AppStream EUS (v. 10.0): Red Hat Enterprise Linux AppStream (v. 10): Red Hat Enterprise Linux AppStream E4S (v.9.2): Red Hat Enterprise Linux AppStream E4S (v.9.4): Red Hat Enterprise Linux AppStream EUS (v.9.6): Red Hat Enterprise Linux AppStream (v. 9): Red Hat Enterprise Linux BaseOS EUS (v. 10.0): Red Hat Enterprise Linux BaseOS (v. 10): Red Hat Enterprise Linux BaseOS (v. 8): Red Hat Enterprise Linux BaseOS AUS (v.8.4): Red Hat Enterprise Linux BaseOS EUS EXTENSION (v.8.4): Red Hat Enterprise Linux BaseOS AUS (v.8.6): Red Hat Enterprise Linux BaseOS EUS EXTENSION (v.8.6): Red Hat Enterprise Linux BaseOS E4S (v.8.8): Red Hat Enterprise Linux BaseOS TUS (v.8.8): Red Hat Enterprise Linux BaseOS E4S (v.9.2): Red Hat Enterprise Linux BaseOS E4S (v.9.4): Red Hat Enterprise Linux BaseOS EUS (v.9.6): Red Hat Enterprise Linux BaseOS (v. 9): Red Hat Enterprise Linux CodeReady Linux Builder EUS (v. 10.0): Red Hat Enterprise Linux CodeReady Linux Builder (v. 10): Red Hat Enterprise Linux CRB (v. 8): Red Hat CodeReady Linux Builder EUS (v.9.6): Red Hat Enterprise Linux CodeReady Linux Builder (v. 9): Red Hat Enterprise Linux Real Time for NFV EUS (v. 10.0): Red Hat Enterprise Linux Real Time for NFV (v. 10): Red Hat Enterprise Linux NFV (v. 8): Red Hat Enterprise Linux Real Time for NFV E4S (v.9.2): Red Hat Enterprise Linux Real Time for NFV E4S (v.9.4): Red Hat Enterprise Linux Real Time for NFV EUS (v.9.6): Red Hat Enterprise Linux Real Time for NFV (v. 9): Red Hat Enterprise Linux Real Time EUS (v. 10.0): Red Hat Enterprise Linux Real Time (v. 10): Red Hat Enterprise Linux RT (v. 8): Red Hat Enterprise Linux Real Time E4S (v.9.2): Red Hat Enterprise Linux Real Time E4S (v.9.4): Red Hat Enterprise Linux Real Time EUS (v.9.6): Red Hat Enterprise Linux Real Time (v. 9): Red Hat Enterprise Linux 7: Red Hat Enterprise Linux 9: Red Hat Enterprise Linux 10:

Exploit Probability

EPSS
0.51%
Percentile
39.63%

EPSS (Exploit Prediction Scoring System) scores estimate the probability that a vulnerability will be exploited in the wild within the next 30 days. The percentile shows you how this score compares to all other vulnerabilities.