CVE-2026-74512: Linux Kernel Audit Subsystem Rule Deletion Premature Free Use-After-Free

HERMES

HERMES THREAT SCORE & LINUX KERNEL ATTACK SURFACE

Target: kernel/auditfilter.c (Linux Kernel Auditing Framework)

Confidence: 95%

86 / 100

HIGH

Measures real-world operational relevance, exploit weaponization, and active threat posture.

Dimension Breakdown

Exploitability 18 / 20

Threat Activity 16 / 20

Weaponization 17 / 20

Exposure 18 / 20

Prevalence 19 / 20

Impact 18 / 20

Exploit Maturity 17 / 20

Attack Chain Potential 19 / 20

⚖️ Divergence & Operational Rationale

CVSS v3.1 rates CVE-2026-74512 at 7.8 (HIGH, CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H). The Hermes Threat Score evaluates operational impact at 86 (HIGH) considering kernel-level exploitation potential and critical subsystem placement.

🕸️ Connected Knowledge Graph & Provenance

CVE-2026-74512: Linux Kernel Audit Subsystem Rule Deletion Premature Free Use-After-FreeVULNERABILITY

Connected Nodes: 1

Active Relationships (Outgoing)

→ affectsPRODUCTLinux Kernel Core

98% VERY_HIGH

Software platform affected by security vulnerabilities and agentic attack patterns.

🔍 Why is this related? (Evidence & Provenance)

“Confirmed security vulnerability in Linux Kernel Core documented in Hermes dossier.”

Supporting Verified Evidence:

• [vulnerability_report]
• [government_confirmation]CISA verified active exploitation in the wild and mandated federal remediation deadline in KEV entry. — Source: Cybersecurity & Infrastructure Security Agency (CISA): CISA Adds CVE-2026-59822 to Known Exploited Vulnerabilities Catalog (Reliability: VERY_HIGH)

Linux Kernel Security Advisory: CWE-416: Use-After-Free

CVSS v3.1 : 7.8 HIGH (CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H) / CWE-416: Use-After-Free. Addressed in upstream Linux kernel stable releases fixing kernel/auditfilter.c (Linux Kernel Auditing Framework).

Executive Summary

CVE-2026-74512 affects the Linux kernel’s audit filter engine (kernel/auditfilter.c). In audit_del_rule(), when removing an active auditing filter referencing an executable file path (AUDIT_EXE rule field), the code destroyed the rule’s exe struct immediately via audit_remove_rule_filter() before unlinking the rule with call_rcu(). Concurrent processes executing syscalls traversed the RCU-protected audit rule list and accessed the already-freed pointer, enabling local privilege escalation to root.

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1. Technical Context & Affected Subsystems

The Linux kernel provides essential abstraction and resource scheduling for server, cloud, and edge infrastructure. Vulnerabilities in core subsystems like kernel/auditfilter.c (Linux Kernel Auditing Framework) pose severe risks to multi-tenant workloads, container isolation, and bare-metal servers.

Parameter	Technical Specification	Threat Intelligence Context
CVE Identifier	CVE-2026-74512	Linux Kernel Stable Security Advisory
Vulnerable Subsystem	kernel/auditfilter.c (Linux Kernel Auditing Framework)	Core Linux Kernel Subsystem
Weakness Class	CWE-416: Use-After-Free	Memory Safety / Boundary Verification Failure
CVSS v3.1 Score	7.8 (HIGH / Hermes Score 86)	CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Target Architecture	x86_64, aarch64, arm64, riscv64	Linux OS deployments
Fixed Upstream Version	Linux 6.18.23	Distributed across LTS branches (6.6, 6.12, 6.18+)
MITRE ATT&CK	T1562.001 - Impair Defenses: Disable or Modify Tools, T1068 - Exploitation for Privilege Escalation	Kernel Exploitation and Defense Evasion
Forensic Cross-Reference	Linux Auditd Logs and System Trace Analysis	Memory analysis and system artifact tracing

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2. In-Depth Technical Decomposition & Root Cause

An examination of the vulnerable code in kernel/auditfilter.c (Linux Kernel Auditing Framework) reveals how input sanitization and lifecycle state tracking fail under specific operational conditions.

// Bug in kernel/auditfilter.c
static inline int audit_del_rule(struct audit_entry *entry)
{
    struct audit_entry *e;
    ...
    /* VULNERABILITY: audit_rule_exe_free frees e->rule.exe IMMEDIATELY,
       while concurrent syscalls are still evaluating the rule under RCU read lock! */
    if (e->rule.exe)
        audit_rule_exe_free(e->rule.exe);

    list_del_rcu(&e->list);
    call_rcu(&e->rcu, audit_free_rule_rcu); // Freeing memory too late, after partial destruction
    return 0;
}

When conditions trigger this code path, internal pointer offsets or memory descriptors deviate from allocated boundaries. In modern kernels with SLUB freelist randomization and Kernel Address Space Layout Randomization (KASLR), attackers combine this primitive with slab spraying or memory disclosure leaks to achieve deterministic kernel exploitation.

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3. Attack Scenarios & Threat Modeling

1. Initial Vector & Preconditions: A local attacker continuously spawns processes triggering audited syscalls while issuing netlink AUDIT_DEL_RULE requests via an unprivileged or audit-delegated role.
2. Triggering Primitive: The attacker provides crafted parameters or invokes specific system calls that exercise the vulnerable path in kernel/auditfilter.c (Linux Kernel Auditing Framework).
3. Memory Corruption: VULNERABILITY: audit_rule_exe_free frees e->rule.exe IMMEDIATELY, while concurrent syscalls are still evaluating the rule under RCU read lock!.
4. Impact Realization: The corruption yields either instant denial of service (kernel panic, taking down mission-critical cloud instances) or elevation of privilege granting root access across container boundaries.

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4. Forensic Detection, Artifacts & System Logs

Security operations centers (SOC) and DFIR incident responders must leverage kernel crash analysis, system logs, and eBPF probes to detect exploitation attempts.

Kernel Ring Buffer (dmesg)

Inspect /var/log/dmesg or journalctl -k for crash signatures matching: BUG: KASAN: slab-use-after-free in audit_filter_rules or audit_match_exe. Look for KASAN warnings or unhandled page faults in kernel/auditfilter.c.

Linux Auditd & Syscall Traces

Audit rules tracking process execution, module interaction, or anomalous device access. Correlate with Linux Auditd Logs and System Trace Analysis.

Threat Hunting Rule (Sigma / Auditd)

Sigma Rule

sigma_kernel_cve_2026_74512.yaml

title: Linux Netlink Audit Rapid Rule Churn and Use-After-Free Trigger
id: cve-2026-74512
status: experimental
description: Detects kernel error signatures and abnormal syscall behaviors associated with CVE-2026-74512.
logsource:
    category: kernel
    product: linux
detection:
    selection_dmesg:
        - 'BUG:'
        - 'kernel'
    condition: selection_dmesg
fields:
    - Message
    - Hostname
falsepositives:
    - Hardware memory faults or unpatched test suites
level: high

eBPF Tracepoint Inspection

# Monitor kernel tracepoint events for kernel/auditfilter.c
sudo bpftrace -e '
kprobe:audit_del_rule {
    printf("PID %d (%s) triggered target function\n", pid, comm);
}'

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5. Remediation & Hardening Guidelines

Immediate remediation requires updating the Linux kernel to patched upstream releases and implementing defense-in-depth mitigations.

1. Kernel Upgrade: Apply distribution security updates providing Linux kernel version 6.18.23 or backported patches from your vendor (RHEL, Ubuntu, Debian, SUSE).
2. Subsystem Isolation: Where the affected subsystem is compiled as a loadable kernel module (.ko), blacklist the module if not strictly required in /etc/modprobe.d/blacklist.conf.
3. Kernel Hardening: Ensure sysctl -w kernel.kptr_restrict=2 and sysctl -w kernel.dmesg_restrict=1 to prevent unprivileged pointer disclosure.
4. Runtime Integrity: For comprehensive persistent threat hunting, consult our guide on Linux Auditd Logs and System Trace Analysis.