CVE-2026-23231
Description
A flaw was found in the Linux kernel. A local attacker with CAP_NET_ADMIN capabilities, or remote packet traffic, could exploit a use-after-free vulnerability in the nf_tables_addchain() function's error handling. Successful exploitation could lead to a kernel crash, resulting in a Denial of Service (DoS), or potentially privilege escalation.
Statement
A use after free can occur in nf_tables_addchain error handling because a new chain is published to table chains via RCU before hook registration completes and is then freed without an RCU grace period when hook registration fails. This creates a race with RCU readers in the control plane such as nf_tables_dump_chains and also with in flight packet evaluation when an IPv4 hook is transiently installed for NFPROTO_INET and later IPv6 hook registration fails. For the CVSS the PR is L because a local actor with CAP_NET_ADMIN can induce the failing add chain path while remote packet traffic may hit the transient hook and trigger the UAF window. Impact ranges from a kernel crash to potential privilege escalation.
Mitigation
In order to trigger the issue, it requires the ability to create user/net namespaces.
On non-containerized deployments of Red Hat Enterprise Linux 7.4 and later, it is recommended to disable user namespaces by setting user.max_user_namespaces to 0:
Make it persistent across reboot
On RHEL 7.4, you can put the setting in /etc/sysctl.conf:
# echo "user.max_user_namespaces=0" | sudo tee -a /etc/sysctl.conf
# sudo sysctl -p
On RHEL8 and above
# echo "user.max_user_namespaces=0" > /etc/sysctl.d/userns.conf
# sysctl -p /etc/sysctl.d/userns.conf
On containerized deployments, such as Red Hat OpenShift Container Platform, do not use this mitigation as the functionality is needed to be enabled.
Common Vulnerability Scoring System (CVSS) Score Details
Info alert:Important note
CVSS scores for open source components depend on vendor-specific factors (e.g. version or build chain). Therefore, Red Hat's score and impact rating can be different from NVD and other vendors. Red Hat remains the authoritative CVE Naming Authority (CNA) source for its products and services (see Red Hat classifications).
CVSS v3 Score Breakdown
| Red Hat | NVD | cve.org | |
|---|---|---|---|
| Base Score | 7.5 | 7.8 | 7.8 |
| Attack Vector | Network | Local | Local |
| Attack Complexity | High | Low | Low |
| Privileges Required | Low | Low | Low |
| User Interaction | None | None | None |
| Scope | Unchanged | Unchanged | Unchanged |
| Confidentiality | High | High | High |
| Integrity Impact | High | High | High |
| Availability Impact | High | High | High |
Vector
Red Hat: CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
NVD: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
cve.org: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Understanding the Weakness (CWE)
Integrity
Technical Impact: Modify Memory
The use of previously freed memory may corrupt valid data, if the memory area in question has been allocated and used properly elsewhere.
Availability
Technical Impact: DoS: Crash, Exit, or Restart
If chunk consolidation occurs after the use of previously freed data, the process may crash when invalid data is used as chunk information.
Confidentiality
Technical Impact: Read Memory
Read operations on freed memory can sometimes leak sensitive information instead of causing a crash
Integrity,Confidentiality,Availability
Technical Impact: Execute Unauthorized Code or Commands
If malicious data is entered before chunk consolidation can take place, it may be possible to take advantage of a write-what-where primitive to execute arbitrary code. If the newly allocated data happens to hold a class, in C++ for example, various function pointers may be scattered within the heap data. If one of these function pointers is overwritten with an address to valid shellcode, execution of arbitrary code can be achieved.
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