CVE-2026-23380 Overview
A vulnerability has been identified in the Linux kernel's tracing subsystem that affects the tracing_buffers_mmap_close function. When a process forks, the child process copies the parent's Virtual Memory Areas (VMAs) but the user_mapped reference count is not properly incremented. This results in a double-call scenario when both parent and child processes exit, triggering a WARN_ON condition when the reference count reaches zero prematurely.
Critical Impact
Local attackers can potentially trigger denial of service conditions or system instability by exploiting the reference count mismatch in the tracing subsystem's memory mapping functionality.
Affected Products
- Linux kernel (versions with vulnerable tracing subsystem)
- Systems using kernel tracing functionality with memory-mapped buffers
- Environments where madvise(MADVISE_DOFORK) can be called by applications
Discovery Timeline
- 2026-03-25 - CVE CVE-2026-23380 published to NVD
- 2026-03-25 - Last updated in NVD database
Technical Details for CVE-2026-23380
Vulnerability Analysis
This vulnerability exists in the Linux kernel's tracing subsystem, specifically in how memory-mapped tracing buffers handle process forking. Under normal circumstances, the tracing buffer memory is mapped with the VM_DONTCOPY flag set, which prevents the VMA from being copied during fork operations. However, this flag is only a hint and can be overridden by an application calling madvise(MADVISE_DOFORK), which resets the VM_DONTCOPY flag.
When an application resets this flag and subsequently forks, both the parent and child processes end up with references to the same tracing buffer mapping. The problem arises because the user_mapped reference count is not incremented when the VMA is copied during the fork. When both processes exit, tracing_buffers_mmap_close() is called twice—once for each process—but the reference count was only set up for a single process. On the second call, user_mapped is already 0, causing the function to return -ENODEV and triggering a WARN_ON that can destabilize the system.
Root Cause
The root cause is an improper reference counting mechanism in the VMA's open callback for tracing buffer mappings. When the VMA is copied during a fork operation (after VM_DONTCOPY has been cleared), the kernel copies the memory mapping to the child process but fails to increment the user_mapped reference counter. This violates the expected invariant that each mapping should have a corresponding reference count entry, leading to a reference count underflow condition when both mappings are closed.
Attack Vector
An attacker with local access can exploit this vulnerability by:
- Opening a tracing buffer and establishing a memory mapping
- Calling madvise(MADVISE_DOFORK) on the mapped region to clear the VM_DONTCOPY flag
- Forking the process to create a child with a copied VMA
- Exiting both processes, which triggers the double-close condition
The vulnerability can result in kernel warnings and potential system instability. While the immediate effect is a WARN_ON condition, repeated exploitation could lead to denial of service conditions or potentially expose other kernel memory corruption issues.
Detection Methods for CVE-2026-23380
Indicators of Compromise
- Presence of WARN_ON messages in kernel logs related to tracing_buffers_mmap_close
- Unexpected -ENODEV errors in tracing subsystem operations
- System instability following fork operations in processes using tracing buffers
Detection Strategies
- Monitor kernel logs for warning messages containing tracing_buffers_mmap_close or reference count errors
- Implement audit rules to track processes calling madvise with MADVISE_DOFORK on tracing-related memory regions
- Use kernel probes or eBPF to monitor fork operations involving memory-mapped tracing buffers
Monitoring Recommendations
- Enable comprehensive kernel logging to capture WARN_ON events in production environments
- Deploy SentinelOne Singularity Platform for real-time kernel-level monitoring and anomaly detection
- Implement alerting for unusual patterns of fork operations combined with tracing subsystem access
How to Mitigate CVE-2026-23380
Immediate Actions Required
- Apply the latest kernel patches from the Linux kernel stable branch
- Review and restrict access to tracing subsystem functionality for non-privileged users
- Consider disabling unnecessary tracing features in production environments until patches are applied
Patch Information
The Linux kernel maintainers have released patches to address this vulnerability. The fix increments the user_mapped reference count in the VMA's open callback without re-mapping the pages, ensuring proper reference counting when VMAs are copied during fork operations. Patches are available through the kernel stable commits:
Workarounds
- Restrict access to /sys/kernel/debug/tracing and related tracing interfaces to trusted users only
- Implement security policies preventing unprivileged users from calling madvise(MADVISE_DOFORK) on sensitive memory regions
- Consider using kernel module parameters or boot configurations to limit tracing functionality exposure
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
