Executive brief
A vulnerability was identified in the Linux kernel's netfilter subsystem, specifically within the tunnel support component. This flaw could allow a local attacker to cause a system crash or potentially execute unauthorized actions by triggering a 'use-after-free' condition when network tunnel objects are destroyed. This impact primarily affects system stability and availability.
Technical details
A use-after-free vulnerability exists in net/netfilter/nft_tunnel.c within the Linux kernel. The function nft_tunnel_obj_destroy() incorrectly calls metadata_dst_free(), which performs an immediate kfree() on metadata_dst without considering the dst_entry reference count. If packets are still queued (e.g., in a netem qdisc) and hold a reference via dst_hold(), they are left with a dangling pointer. When these packets are later dequeued and processed by dst_release(), the kernel operates on already freed memory. The fix replaces metadata_dst_free() with dst_release() to ensure memory is only reclaimed after all active references are dropped.
Affected products
- Linux Linux 4.19 through 6.9.x
Timeline
- 2026-05-27: other: Vulnerability fixed in upstream source code
- 2026-06-25: advisory: CVE published by NVD
References
- https://git.kernel.org/stable/c/349df61526d2e39decc685d246202e3e284cfe05
- https://git.kernel.org/stable/c/55b79b1ae42372012413ce0413181d26679b17ef
- https://git.kernel.org/stable/c/5e9ee18b27fde88cb6148202b33916c66693fe82
- https://git.kernel.org/stable/c/8767fe4079affa74314d7eb3220e700150289842
- https://git.kernel.org/stable/c/941d7394efda5e054e2d6f3e0dd0f6a9ba19aaa3
- https://git.kernel.org/stable/c/c32b26aaa2f9216520a38b3f4bfeec846eb3eb8a
- https://git.kernel.org/stable/c/f9a0e4b61054cde89a2a77845293c726cc07cc43