Executive brief
A vulnerability in the Linux kernel's networking subsystem could allow a local user to gain elevated privileges. The issue occurs in the 'act_ct' component, which handles network traffic flow tables. By exploiting a race condition, an attacker could cause the system to use memory that has already been freed, potentially leading to a system crash or unauthorized access to sensitive data.
Technical details
A use-after-free (UAF) vulnerability exists in the Linux kernel's net/sched: act_ct component. In tcf_ct_flow_table_get(), the function rhashtable_lookup_fast() is used to retrieve a flow table object (ct_ft). This helper internally manages its own RCU read critical section, releasing the lock before returning the object. This creates a race window where the object can be freed by tcf_ct_flow_table_cleanup_work() before the caller can increment its reference count via refcount_inc_not_zero(). A local attacker can exploit this race condition to achieve privilege escalation. The fix involves manually holding the rcu_read_lock() across both the lookup and the reference count increment.
Affected products
- Linux Linux Kernel versions prior to 6.14.y, 6.13.y, 6.12.y, 6.11.y, 6.10.y, 6.6.y, 6.1.y, 5.15.y, 5.10.y, 5.4.y
Timeline
- 2026-04-10: disclosed: Vulnerability reported by ZDI and patch authored
- 2026-05-23: patched: Patch committed to stable trees
- 2026-06-09: advisory: CVE published in NVD
References
- https://git.kernel.org/stable/c/17dfb67cb399b660105d9a8c6100851c0d0cdc70
- https://git.kernel.org/stable/c/3e20e1b3058e0b94638e7b931c138e840e266724
- https://git.kernel.org/stable/c/4c727c6967a41b37efe0f26332ca9ec5b74785a3
- https://git.kernel.org/stable/c/67c9ecc9f2575273ed1323e312881fc98ac83d6d
- https://git.kernel.org/stable/c/a2e0c045c87aa252eb61412e67dd91f2c2b19f81
- https://git.kernel.org/stable/c/ece578ca61e572df96cfc80456357ebfae0b4b9e
- https://git.kernel.org/stable/c/f23424a0ddadb494d4bd57056a7ca703312d3a7b