CVE-2026-80876
NoneCVSS
—
EPSS
0.2%
Published
Sep 4, 2026
CISA due date
—
Cloudanix analysis
On certain computer systems the kernel's event recording feature was reporting wrong sizes for small recorded events, which could make monitoring and debugging less reliable.
- Exploitation
- Other
- Attacker needs
- Local User
- Complexity
- Theoretical
- Impact
- Other
- Component
- OS kernel
- Class
- Other
- Remediation
- Patch
- Effort
- Low
- Patch risk
- Low
What it actually does
The ring buffer event length calculation in rb_calculate_event_length() and ring_buffer_event_length() incorrectly handles the extra 4-byte length field reservation when RB_FORCE_8BYTE_ALIGNMENT is true, causing small events (<= RB_MAX_SMALL_DATA) to report a data length inflated by 4 bytes on affected architectures.
Why it matters to the business
Kernel tracing and debugging tools produce inaccurate event size reports on specific architectures, potentially leading to incorrect analysis of system behavior or performance data without affecting core system stability or security.
How an attack unfolds
No realistic exploitation path exists; the flaw is a correctness error in tracing metadata reporting rather than a memory safety or privilege issue, with no evidence of use by threat actors or ransomware campaigns.
How to fix it
Apply the upstream kernel patch that conditions the length field subtraction on RB_FORCE_8BYTE_ALIGNMENT being true; rebuild and deploy updated kernels for riscv64 or other affected configurations with CONFIG_HAVE_64BIT_ALIGNED_ACCESS enabled.
How to confirm the fix worked
Execute ftrace selftests including trace_marker_raw.tc on affected hardware and confirm that reported data field counts remain consistent (8*N+4) across all event IDs rather than exhibiting the 8*N vs 8*N+4 discontinuity.
How to detect it
Review ftrace or ring-buffer logs and selftest output for anomalous event length patterns on riscv64 or similar platforms; inspect kernel build configuration for RB_FORCE_8BYTE_ALIGNMENT usage.
What your security team should do
- Prioritize kernel updates for systems using ftrace or ring-buffer tracing on alignment-forcing architectures
- Validate tracing output accuracy in test environments before production deployment
- Monitor upstream stable kernel releases for the ring-buffer alignment fix
The record
In the Linux kernel, the following vulnerability has been resolved: ring-buffer: Fix event length with forced 8-byte alignment When RB_FORCE_8BYTE_ALIGNMENT is true, rb_calculate_event_length() reserves the space of event->array[0] for placing the data length and rb_update_event() stores the data length in event->array[0] accordingly. As a result the whole event length will add extra 4 bytes for sizeof(event.array[0]) unconditionally. But ring_buffer_event_length() only subtracts the sizeof(event->array[0]) for events larger than RB_MAX_SMALL_DATA + sizeof(event->array[0]). As a result, small events on architectures with RB_FORCE_8BYTE_ALIGNMENT=true report a data length that is 4 bytes larger than expected. To fix it, add the RB_FORCE_8BYTE_ALIGNMENT as a condition to subtract the size of that length field whenever RB_FORCE_8BYTE_ALIGNMENT is true. This issue is observed in a riscv64 kernel with CONFIG_HAVE_64BIT_ALIGNED_ACCESS set to y, when we run ftrace selftest trace_marker_raw.tc, we get the weird log: for cases where the id is 1..100, the number of data field is 8*N, but once id exceeds 100, the number of data field becomes 8*N+4: # 1 buf: 58 00 00 00 80 5e d1 63 (number of data field is 8*1) ... # a buf: 58 ... (number of data field is 8*2) ... # 64 buf: 58 ... (number of data field is 8*13) # 65 buf: 58 ... (number of data field is 8*13+4) After applying this change, the number of data field keeps being 8*N+4 consistently.
Affected packages
| Ecosystem | Package | Introduced | Fixed |
|---|