Detect Linux Kernel Incorrect Resource Transfer Between Spheres (CVE-2026-31431) in Splunk
CVE-2026-31431 is a Linux Kernel vulnerability classified as CWE-669 (Incorrect Resource Transfer Between Spheres). The flaw allows improper transfer of resources across security boundaries within the kernel, potentially enabling privilege escalation or unauthorized memory access. This vulnerability is listed in the CISA Known Exploited Vulnerabilities catalog, indicating active exploitation in the wild. Attackers with local access may exploit this to escalate privileges to root or escape container boundaries.
MITRE ATT&CK
SPL Detection Query
index=linux_logs (sourcetype=syslog OR sourcetype=linux_secure OR sourcetype=linux_audit)
| where (source="/var/log/kern.log" OR source="/var/log/messages" OR source="/dev/log")
AND (message LIKE "%copy_to_user%" OR message LIKE "%copy_from_user%" OR message LIKE "%__copy_overflow%"
OR message LIKE "%BUG: unable to handle%" OR message LIKE "%general protection fault%"
OR message LIKE "%use-after-free%" OR message LIKE "%kernel NULL pointer%"
OR message LIKE "%out-of-bounds%")
| eval severity_level=case(
match(message, "BUG:|Oops:|kernel panic"), "critical",
match(message, "general protection|use-after-free"), "high",
true(), "medium")
| stats count AS event_count, earliest(_time) AS first_seen, latest(_time) AS last_seen, values(message) AS kernel_messages BY host, severity_level
| where event_count > 0
| sort - last_seenSplunk query to identify Linux kernel resource transfer boundary violations associated with CVE-2026-31431, correlating kernel log fault messages that indicate improper cross-sphere memory access or copy operations.
Data Sources
Required Sourcetypes
False Positives & Tuning
- Kernel bug reports from crash reporters or automated diagnostic tools unrelated to exploitation
- Memory fault messages triggered by hardware errors or RAM issues rather than software exploitation
- Development or staging hosts running experimental kernel modules that produce intentional fault messages
Other platforms for CVE-2026-31431
Testing Methodology
Validate this detection against 3 adversary techniques from Atomic Red Team. Each test below lists the behaviour to exercise and the telemetry you should expect to see. Executable commands and cleanup steps are available with Pro.
- Test 1Simulate kernel copy boundary fault via /proc/kcore read attempt
Expected signal: Kernel message in dmesg showing access denial or fault; audit log SYSCALL record for 'open' or 'read' on /proc/kcore by non-root UID; possible kernel warning message about unauthorized memory access attempt
- Test 2Privilege escalation simulation via SUID binary abuse on unpatched kernel
Expected signal: Audit log SYSCALL record showing execve of test_suid with uid!=0 but euid=0; EDR process event showing SUID execution; possible AppArmor/SELinux denial log if MAC policy is enforced
- Test 3Container escape boundary test via /proc/sysrq-trigger probe
Expected signal: Host kernel log entries showing container namespace probe attempts; Docker daemon log entries for the test container; audit log entries showing file access attempts to /dev/mem or /proc/1/ from container process
Response Playbook
Triage
- Verify the affected Linux host's kernel version against the patched releases referenced in the kernel stable git tree (https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/about/) to confirm vulnerability exposure before escalating.
- Check /var/log/kern.log, /var/log/syslog, and dmesg output for kernel OOPS, BUG, or general protection fault messages timestamped around the detection alert to determine if exploitation was attempted or successful.
- Identify the process tree that triggered the alert using 'ps auxf' and 'pstree -p' at time of detection, correlating with audit logs from /var/log/audit/audit.log to determine the originating user and parent process.
- Assess whether the affected host is a container host (Kubernetes node, Docker host) — CVE-2026-31431 may enable container escape in addition to local privilege escalation, significantly widening blast radius.
- Query your EDR or SIEM for lateral movement indicators from the affected host IP within 1 hour before and after the kernel fault timestamp, as successful exploitation may be followed immediately by credential harvesting or lateral movement.
Containment
- Isolate the affected Linux host at the network level (firewall rule blocking all outbound except management) immediately if kernel exploitation is confirmed, preventing post-exploitation lateral movement while preserving forensic state.
- Do NOT reboot the host until memory forensics have been captured — reboot destroys volatile evidence of in-memory exploitation artifacts. Use 'virsh dump' or LiME kernel module to capture a memory image before any restart.
- Revoke active SSH sessions and rotate credentials for all accounts that had active sessions on the host during the exploitation window, as compromised root access enables full credential extraction from /etc/shadow and memory.
Evidence Collection
- Capture a full memory image using the LiME (Linux Memory Extractor) kernel module: 'insmod lime.ko path=/tmp/memory.lime format=lime' — this preserves kernel heap state showing the resource transfer boundary violation in situ.
- Preserve the following artifacts before any remediation: /var/log/kern.log, /var/log/audit/audit.log, /proc/[suspicious_pid]/maps, /proc/[suspicious_pid]/cmdline, bash history for all users (~/.bash_history, /root/.bash_history), and a copy of currently loaded kernel modules via 'lsmod > /tmp/lsmod.txt'.
- Collect network connection state with 'ss -tulpn > /tmp/netstat.txt' and 'ip route > /tmp/routes.txt' to identify any backdoor listeners or routing changes made post-exploitation.
Escalation Criteria
- !Escalate immediately to incident response if evidence shows successful privilege escalation to root (UID=0 process with non-root parent in audit logs), as the host must be treated as fully compromised and all secrets it could access (Vault tokens, SSH keys, service credentials) rotated.
- !Escalate to CISO and legal/compliance if the compromised host processes PII, PHI, PCI data, or holds credentials for cloud infrastructure — CVE-2026-31431 KEV status indicates active exploitation and may trigger mandatory breach notification timelines.
Investigation Guide
Related Techniques
Forensic Artifacts
- >
Kernel OOPS or BUG trace in /var/log/kern.log or dmesg output containing 'copy_to_user', 'copy_from_user', or '__copy_overflow' stack frames near the time of exploitation - >
Audit log entries in /var/log/audit/audit.log showing SYSCALL records for process that changed UID from non-root to root (uid=X euid=0) without a legitimate sudo/su invocation - >
Unexpected setuid binaries or new entries in /etc/sudoers or /etc/sudoers.d/ created after the exploitation timestamp, indicating persistence mechanisms installed by the attacker - >
Loaded kernel modules not present in the system's package manager database (dpkg -l | grep linux-modules or rpm -qa | grep kernel) that may represent rootkit persistence
Tuning Guidance
This detection will generate noise on Linux hosts running kernel crash testing frameworks (kdump, kexec), hosts with failing RAM (hardware memory errors produce similar kernel messages), and development systems running kernel debug builds with KASAN/UBSAN enabled. Suppress alerts from hosts tagged as 'kernel-dev' or 'staging-test' in your asset inventory. For high-fidelity tuning, combine kernel fault messages with a correlated privilege escalation event (UID transition to 0) within a 60-second window — this significantly reduces false positives while preserving detection of actual exploitation chains. Additionally, establish a baseline of 'normal' kernel fault rate per host over 14 days and alert only on statistically significant spikes above the host's historical baseline.
Hunting Queries
30-day retrospective hunt for Linux kernel resource transfer fault messages across all monitored Linux hosts to identify potential historical exploitation of CVE-2026-31431 or related kernel copy vulnerabilities that may have preceded the detection rule deployment.
Syslog
| where TimeGenerated > ago(30d)
| where Facility =~ "kern"
| where SyslogMessage has_any ("copy_to_user", "copy_from_user", "__copy_overflow", "BUG:", "Oops:", "general protection fault")
| summarize EventCount=count(), FirstSeen=min(TimeGenerated), LastSeen=max(TimeGenerated), SampleMessages=make_set(SyslogMessage, 5) by Computer
| where EventCount > 0
| order by LastSeen descindex=linux_logs sourcetype=syslog earliest=-30d
| rex field=_raw "kernel: (?<kernel_msg>.+)"
| where match(kernel_msg, "copy_to_user|copy_from_user|__copy_overflow|BUG:|Oops:|general protection fault")
| stats count AS fault_count, earliest(_time) AS first_seen, latest(_time) AS last_seen, values(kernel_msg) AS messages BY host
| sort - last_seenAtomic Red Team Tests
Attempts to read from /proc/kcore as an unprivileged user to trigger kernel memory access boundary enforcement, simulating the class of access that CVE-2026-31431 bypasses. This does not exploit the CVE but generates similar telemetry.
Command
# Run as non-root user in isolated lab VM
id
dd if=/proc/kcore of=/tmp/kcore_sample bs=4096 count=1 2>&1 || echo 'Expected: permission denied or kernel fault'
dmesg | tail -20Cleanup
rm -f /tmp/kcore_sampleExpected Telemetry
Kernel message in dmesg showing access denial or fault; audit log SYSCALL record for 'open' or 'read' on /proc/kcore by non-root UID; possible kernel warning message about unauthorized memory access attempt
Expected Detection
Syslog/kern.log kernel message detected by the query; QRadar/Sentinel alert fires on kernel boundary message pattern
In a controlled lab environment with a known-vulnerable kernel version, uses a crafted SUID binary to test privilege escalation detection telemetry without executing an actual exploit payload. Tests detection of UID transition to root.
Command
# LAB ONLY — requires unpatched kernel in isolated VM with no network
# Create test SUID binary that logs the UID transition for telemetry testing
cat > /tmp/test_suid.c << 'EOF'
#include <stdio.h>
#include <unistd.h>
int main() { printf("EUID: %d\n", geteuid()); return 0; }
EOF
gcc -o /tmp/test_suid /tmp/test_suid.c
# As root, set SUID bit (simulates post-exploitation artifact)
chmod u+s /tmp/test_suid
# Run as non-root to generate UID-0 execution telemetry
su -c '/tmp/test_suid' testuser 2>/dev/null
# Check audit log for SYSCALL record
ausearch -k suid_exec 2>/dev/null || grep 'test_suid' /var/log/audit/audit.log | tail -5Cleanup
rm -f /tmp/test_suid /tmp/test_suid.c; userdel testuser 2>/dev/null || trueExpected Telemetry
Audit log SYSCALL record showing execve of test_suid with uid!=0 but euid=0; EDR process event showing SUID execution; possible AppArmor/SELinux denial log if MAC policy is enforced
Expected Detection
CrowdStrike Falcon PrivilegeEscalationDetected event; SIEM alert on SUID binary execution by non-privileged user context
From inside a Docker container on a lab host, probes kernel interface files that should be inaccessible from within the container namespace, generating telemetry for the container escape detection path of CVE-2026-31431.
Command
# LAB ONLY — run inside Docker container on isolated test host
# Start test container
docker run --rm -it --name cve_2026_31431_test ubuntu:22.04 bash -c '
echo "Container UID: $(id)"
# Probe kernel interfaces that should be namespace-isolated
cat /proc/sysrq-trigger 2>&1 || echo "Blocked as expected"
ls -la /proc/1/ns/ 2>&1
cat /proc/1/cmdline 2>/dev/null && echo "WARNING: accessed host PID 1" || echo "PID namespace isolated"
# Probe /dev/mem (should fail in unprivileged container)
dd if=/dev/mem bs=1 count=1 2>&1 || echo "dev/mem blocked"
'
# On host: check kernel log for any boundary fault messages
dmesg | tail -30 | grep -E 'namespace|container|cgroup|fault'Cleanup
docker rm -f cve_2026_31431_test 2>/dev/null || trueExpected Telemetry
Host kernel log entries showing container namespace probe attempts; Docker daemon log entries for the test container; audit log entries showing file access attempts to /dev/mem or /proc/1/ from container process
Expected Detection
Chronicle YARA-L rule triggers on /proc/*/mem access pattern; Elastic EQL sequence detects file access to kernel interfaces followed by attempted privilege boundary crossing