CVE-2026-74602 Overview
CVE-2026-74602 is a Linux kernel vulnerability in the tracing ring-buffer subsystem. The flaw resides in the rb_allocate_cpu_buffer() function, where the bpage->order field was not initialized and defaulted to zero. When the ring-buffer is configured with sub-buffers larger than PAGE_SIZE, this mismatch causes incorrect page-order handling during buffer teardown. The free_buffer_page() routine relies on bpage->order to release the correct number of contiguous pages. An incorrect order value leads to memory management inconsistencies when freeing reader pages allocated with a higher order than expected.
Critical Impact
Incorrect page-order accounting in the ring-buffer reader page can cause improper memory release when sub-buffer sizes exceed PAGE_SIZE, resulting in kernel memory corruption or leaks during ring-buffer deallocation.
Affected Products
- Linux kernel versions containing the ring-buffer sub-buffer order feature prior to the fix commits
- Distributions shipping affected upstream kernel trees
- Systems using the tracing ring-buffer with subbuf_order greater than zero
Discovery Timeline
- 2026-08-22 - CVE-2026-74602 published to NVD
- 2026-08-23 - Last updated in NVD database
Technical Details for CVE-2026-74602
Vulnerability Analysis
The vulnerability is an uninitialized memory use issue [CWE-908] in the Linux kernel ring-buffer implementation used by the tracing subsystem. In rb_allocate_cpu_buffer(), the reader page structure is allocated and its associated backing pages are obtained using the ring-buffer's configured subbuf_order. However, the bpage->order field on the reader page descriptor was never assigned. This leaves bpage->order at its default value of 0.
The kernel's free_buffer_page() helper uses bpage->order to determine how many contiguous pages to release back to the page allocator. When subbuf_order is non-zero, meaning sub-buffers are larger than a single page, the reader page carries a higher-order allocation, but the descriptor claims order 0. The mismatch produces incorrect deallocation accounting during ring-buffer teardown or reconfiguration.
Root Cause
The root cause is a missing field assignment during initialization. The bpage->order member on the reader page descriptor was omitted in rb_allocate_cpu_buffer(), so it did not reflect the actual allocation size used by the buffer. The fix aligns bpage->order with buffer::subbuf_order, ensuring the descriptor accurately represents the page-order used at allocation time.
Attack Vector
Exploitation requires local access with the ability to configure the tracing ring-buffer sub-buffer order, typically via tracefs interfaces such as /sys/kernel/tracing/buffer_subbuf_size_kb. Access to these interfaces is normally restricted to privileged users. Triggering the fault requires setting a non-zero subbuf_order and then releasing or reconfiguring per-CPU ring-buffers. Public exploit code is not available and the flaw has not been listed on the CISA KEV catalog.
See the upstream fix in the Kernel Git Commit 2e37f2b and related stable backports for technical details.
Detection Methods for CVE-2026-74602
Indicators of Compromise
- Kernel warnings or BUG: messages originating from the page allocator during tracing ring-buffer resize or shutdown operations
- Unexpected kernel oops or slab corruption reports referencing free_buffer_page or rb_free_cpu_buffer in stack traces
- Unexplained kernel memory growth on systems where tracing has been reconfigured with non-default subbuf_order
Detection Strategies
- Inventory running kernels and compare against fixed versions referenced in the upstream stable commits
- Audit access to tracefs and debugfs mount points to identify processes modifying buffer_subbuf_size_kb
- Correlate kernel log anomalies with tracing configuration changes to identify potential trigger events
Monitoring Recommendations
- Ship kernel logs (dmesg, journald) to a central store and alert on ring-buffer or page allocator warnings
- Monitor process activity that writes to /sys/kernel/tracing/ and /sys/kernel/debug/tracing/ paths
- Track kernel package versions across the fleet to flag hosts still running vulnerable builds
How to Mitigate CVE-2026-74602
Immediate Actions Required
- Apply the vendor-supplied kernel update that includes the rb_allocate_cpu_buffer() initialization fix
- Identify systems using non-default tracing sub-buffer sizes and prioritize them for patching
- Restrict access to tracefs and debugfs to root and trusted administrative accounts only
Patch Information
The issue is resolved upstream in the Linux kernel by initializing bpage->order to match buffer::subbuf_order in rb_allocate_cpu_buffer(). Fix commits are available at Kernel Git Commit 2e37f2b, Kernel Git Commit 3b3e0a6, Kernel Git Commit 6d014e4, and Kernel Git Commit 7c620d8. Rebuild or install distribution kernels containing these backports.
Workarounds
- Leave the tracing ring-buffer at its default subbuf_order of 0 until patched kernels are deployed
- Unmount or restrict tracefs on systems that do not require kernel tracing in production
- Limit membership in groups permitted to interact with the tracing subsystem
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
