CVE-2026-23010: Linux Kernel Use-After-Free Vulnerability

CVE-2026-23010 Overview

CVE-2026-23010 is a use-after-free vulnerability in the Linux kernel's IPv6 address configuration subsystem. The vulnerability exists in the inet6_addr_del() function within net/ipv6/addrconf.c, where a race condition allows access to freed memory when deleting IPv6 addresses. This flaw was discovered by the syzbot automated fuzzing system and affects systems running vulnerable kernel versions with IPv6 enabled.

The vulnerability occurs because a previous commit accidentally moved the ipv6_del_addr() call for mngtmpaddr addresses before reading the ifp->flags field for temporary addresses. This ordering error causes the code to access the inet6_ifaddr structure after it has already been freed, triggering a classic use-after-free condition.

Critical Impact

Local attackers with network configuration privileges could exploit this use-after-free vulnerability to potentially execute arbitrary code in kernel context, crash the system causing denial of service, or leak sensitive kernel memory contents.

Affected Products

• Linux kernel (versions prior to the patch commits)
• Systems with IPv6 networking enabled
• Network equipment and servers running vulnerable Linux kernel versions

Discovery Timeline

• 2026-01-25 - CVE-2026-23010 published to NVD
• 2026-01-26 - Last updated in NVD database

Technical Details for CVE-2026-23010

Vulnerability Analysis

This use-after-free vulnerability occurs in the IPv6 address management code path when handling the deletion of managed temporary addresses (mngtmpaddr). The inet6_addr_del() function is responsible for removing IPv6 addresses from network interfaces through the socket ioctl interface.

The vulnerability manifests when processing ioctl operations (specifically SIOCDIFADDR with ioctl number 0x8936) through the inet6_ioctl() handler. A local process with appropriate permissions can trigger address deletion operations that expose the race condition.

The KASAN (Kernel Address Sanitizer) report indicates a read operation of 4 bytes from freed memory at address ffff88807b89c86c, specifically at line 3117 of addrconf.c. The freed memory was originally allocated by ipv6_add_addr() for an inet6_ifaddr structure and later freed via the RCU (Read-Copy-Update) mechanism through kvfree_rcu_bulk().

Root Cause

The root cause is an incorrect ordering of operations in the inet6_addr_del() function. A previous kernel commit inadvertently moved the ipv6_del_addr() call—which frees the inet6_ifaddr structure—before the code that reads ifp->flags to check for temporary addresses.

This creates a temporal violation where:

1. ipv6_del_addr() is called, which initiates freeing of the inet6_ifaddr structure
2. The code subsequently attempts to read ifp->flags from the now-freed structure
3. The read operation accesses deallocated memory, causing undefined behavior

The fix involves reordering these operations so that all reads from the inet6_ifaddr structure complete before ipv6_del_addr() is invoked.

Attack Vector

The attack vector requires local access to the system with sufficient privileges to perform network interface configuration operations. An attacker would need to:

1. Obtain local access to a system running a vulnerable kernel version
2. Have permissions to execute network ioctl operations (typically root or CAP_NET_ADMIN capability)
3. Trigger IPv6 address deletion operations that exercise the vulnerable code path
4. Time the operations to exploit the use-after-free condition

The vulnerability is exploitable through the standard socket ioctl interface, making it accessible to processes with network administration capabilities. The syzbot fuzzer was able to trigger this consistently, indicating the race window may be relatively wide.

Detection Methods for CVE-2026-23010

Indicators of Compromise

• KASAN (Kernel Address Sanitizer) reports indicating slab-use-after-free in inet6_addr_del or related functions
• Kernel panic or oops messages referencing addrconf.c around line 3117
• Unexpected system crashes during IPv6 address configuration operations
• Anomalous behavior when adding or removing IPv6 addresses from network interfaces

Detection Strategies

• Enable KASAN in kernel builds to detect use-after-free conditions during testing and development
• Monitor kernel log messages (dmesg) for memory corruption reports related to IPv6 subsystem
• Deploy runtime memory debugging tools to identify exploitation attempts
• Implement system call auditing for ioctl operations on AF_INET6 sockets

Monitoring Recommendations

• Configure centralized logging for kernel messages across all Linux systems
• Set up alerts for KASAN or KFENCE memory error reports in production environments
• Monitor for unusual patterns of IPv6 address configuration changes
• Implement anomaly detection for network interface ioctl activity

How to Mitigate CVE-2026-23010

Immediate Actions Required

• Update the Linux kernel to a patched version containing one of the fix commits
• Review systems for any signs of exploitation attempts in kernel logs
• Restrict access to network administration capabilities (CAP_NET_ADMIN) to trusted users only
• Consider temporarily disabling IPv6 on critical systems if patching is not immediately possible

Patch Information

The Linux kernel development team has released fixes for this vulnerability through multiple stable kernel branches. The following commits address the use-after-free issue by reordering the ipv6_del_addr() call after all necessary reads from the inet6_ifaddr structure:

• Kernel Git Commit 2684610
• Kernel Git Commit 8b6dcb5
• Kernel Git Commit ddf96c3

System administrators should apply kernel updates from their distribution vendor or compile a patched kernel from the stable kernel sources.

Workarounds

• Restrict CAP_NET_ADMIN capability using Linux capabilities or container security policies
• Disable IPv6 at boot time by adding ipv6.disable=1 to kernel command line parameters
• Use SELinux or AppArmor policies to limit which processes can perform network configuration
• Implement network namespace isolation to contain potential exploitation attempts

# Temporary workaround: Disable IPv6 system-wide
echo 1 > /proc/sys/net/ipv6/conf/all/disable_ipv6
echo 1 > /proc/sys/net/ipv6/conf/default/disable_ipv6

# Persistent workaround: Add to /etc/sysctl.conf
# net.ipv6.conf.all.disable_ipv6 = 1
# net.ipv6.conf.default.disable_ipv6 = 1