CVE-2025-38212: Linux Kernel Use-After-Free Vulnerability

CVE-2025-38212 Overview

CVE-2025-38212 is a use-after-free vulnerability [CWE-416] in the Linux kernel's Inter-Process Communication (IPC) subsystem. The flaw exists in shm_destroy_orphaned(), where idr_for_each() traversals are protected by rwsem but not by a Read-Copy-Update (RCU) read-critical region. When radix_tree_node_free() frees a radix_tree_node through call_rcu(), subsequent reads in radix_tree_for_each_slot() can access already-freed memory. Syzbot discovered the flaw during automated kernel fuzzing. The vulnerability affects the Linux kernel and Debian Linux 11.0 distributions.

Critical Impact
A local, authenticated attacker can trigger memory corruption in kernel space, leading to privilege escalation, denial of service, or arbitrary code execution in ring 0.

Affected Products

Linux Kernel (multiple stable branches prior to the fix commits)
Debian Linux 11.0
Siemens products incorporating affected kernel versions (per Siemens Security Advisory SSA-082556)

Discovery Timeline

2025-07-04 - CVE-2025-38212 published to the National Vulnerability Database
2026-07-30 - Last updated in NVD database

Technical Details for CVE-2025-38212

Vulnerability Analysis

The vulnerability resides in the System V shared memory (shm) IPC cleanup path. Specifically, shm_destroy_orphaned() invokes idr_for_each() to iterate over IPC identifiers held in an IDR (integer ID allocator) structure backed by a radix tree. The kernel's radix tree implementation defers node reclamation using call_rcu(), expecting readers to hold the RCU read lock during traversal.

While rwsem provides mutual exclusion against writers, it does not defer RCU grace periods. When a concurrent path removes IPC entries, radix_tree_node_free() schedules node deallocation via RCU. Without an enclosing rcu_read_lock(), the pending free can complete between iterations of radix_tree_for_each_slot(). The subsequent slot dereference reads freed heap memory.

Exploitation of use-after-free conditions in kernel memory typically enables attackers to corrupt adjacent objects, hijack function pointers, or overwrite credential structures to gain root privileges.

Root Cause

The root cause is missing RCU read-side critical section coverage around idr_for_each() in shm_destroy_orphaned(). The IPC subsystem relied on rwsem for serialization but failed to account for the RCU-deferred freeing semantics of the underlying radix tree. This design mismatch created a race window between node reclamation and iterator dereference.

Attack Vector

A local attacker with the ability to create and destroy System V shared memory segments can race IPC namespace cleanup against concurrent IPCS lookups. Triggering the race requires precise timing of shmctl() operations across processes or namespaces. Successful exploitation corrupts kernel memory and can be leveraged for local privilege escalation.

No verified exploit code has been publicly released. See the kernel patch d66adabe and related commits for the authoritative fix details.

Detection Methods for CVE-2025-38212

Indicators of Compromise

Unexpected kernel oops or general protection fault messages referencing shm_destroy_orphaned, idr_for_each, or radix_tree_for_each_slot in dmesg or /var/log/kern.log.
KASAN (Kernel Address Sanitizer) reports flagging use-after-free reads within the IPC or radix tree code paths on instrumented builds.
Unexplained crashes or panics during heavy IPC workload cleanup, particularly in containerized environments performing frequent namespace teardown.

Detection Strategies

Inventory kernel versions across Linux fleets and correlate against the fix commits listed in the Linux kernel stable tree.
Monitor for anomalous shmget(), shmat(), and shmctl() syscall patterns from low-privileged processes using auditd or eBPF-based syscall telemetry.
Deploy vulnerability scanners that consume NVD feeds and flag hosts running unpatched kernel versions listed under the affected CPE URIs.

Monitoring Recommendations

Enable kernel crash dump collection (kdump) so that use-after-free crashes produce forensic artifacts for post-incident analysis.
Alert on kernel ring buffer entries containing KASAN or slab corruption signatures, forwarding them to a centralized log platform.
Track privilege escalation indicators such as unexpected UID transitions to root by non-root parent processes.

How to Mitigate CVE-2025-38212

Immediate Actions Required

Apply the vendor-supplied kernel updates from your Linux distribution. Debian LTS users should install the packages referenced in Debian LTS Announcement #00007 and Debian LTS Announcement #00008.
Prioritize patching multi-tenant hosts, container orchestration nodes, and shared build systems where local users have shell access.
Review Siemens deployments against Siemens Security Advisory SSA-082556 and follow vendor-specific remediation.

Patch Information

The fix wraps the idr_for_each() invocation in shm_destroy_orphaned() inside an RCU read-critical section. Backports are available across multiple stable branches via commits d66adabe, 5180561a, 5f1e1573, 68c173ea, 74bc813d, 78297d53, b0b6bf90, and b968ba8b.

Workarounds

Restrict local shell access on multi-tenant systems until kernels are patched, since the attack requires local, authenticated access.
Constrain use of System V IPC by unprivileged workloads through seccomp filters that block shmget, shmat, shmdt, and shmctl where these syscalls are not required.
Isolate untrusted workloads in dedicated hosts or virtual machines so that a kernel-level compromise cannot pivot into shared infrastructure.

bash

# Verify running kernel and confirm patch level after update
uname -r
apt list --installed 2>/dev/null | grep -E 'linux-image|linux-headers'

# Debian/Ubuntu: apply available kernel updates and reboot
sudo apt update && sudo apt upgrade -y
sudo reboot

# Optional: block System V shared memory syscalls for a workload via seccomp
# (example policy fragment for container runtimes)
# {"syscalls": [{"names": ["shmget","shmat","shmdt","shmctl"], "action": "SCMP_ACT_ERRNO"}]}