CVE-2026-68174 tracing: Fix union collision of module and refcnt for dynamic events
A local attacker with low privileges can cause a kernel crash by triggering a null pointer dereference in the Linux kernel tracing subsystem via dynamic events.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-68174?
CVE-2026-68174 is a vulnerability in Linux, published on 10 Aug 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Official description
In the Linux kernel, the following vulnerability has been resolved:
tracing: Fix union collision of module and refcnt for dynamic events
In 'struct trace_event_call', the 'module' pointer and the 'refcnt' atomic variable share the same memory space in a union. For dynamic events, the union member is 'refcnt', which acts as an active reference counter.
When a dynamic event (such as kprobe, uprobe, fprobe, eprobe, or wprobe) has a non-zero reference count (e.g. due to active event triggers or perf attachments), its 'call->module' evaluates to a small non-zero integer instead of NULL.
When filtering or setting events for a specific module (e.g., writing ':mod:<module>' to 'set_event'), the code in '__ftrace_set_clr_event_nolock()' and 'update_event_fields()' reads 'call->module' directly without checking whether the event is dynamic. This causes the kernel to treat the small integer (refcnt) as a 'struct module' pointer, leading to a NULL/invalid pointer dereference (Oops) when dereferencing the module name.
Fix this by ensuring that the 'TRACE_EVENT_FL_DYNAMIC' flag is checked before treating 'call->module' as a valid pointer in these code paths.
Which versions are affected by CVE-2026-68174?
How do I fix CVE-2026-68174?
Apply the vendor's patch.
Is CVE-2026-68174 being exploited?
There is no known exploitation of CVE-2026-68174 in the wild and no public exploit code.
Sources
Also known as BELL-CVE-2026-68174, DEBIAN-CVE-2026-68174, GHSA-c2f7-rhw7-9m5r, UBUNTU-CVE-2026-68174.