CVE-2026-68377 in Linux
Summary
by MITRE • 08/10/2026
In the Linux kernel, the following vulnerability has been resolved:
net/sched: act_tunnel_key: Defer dst_release to RCU callback
Fix a race-condition use-after-free in tunnel_key_release_params().
The function releases the metadata_dst of the old params synchronously via dst_release() while deferring the params struct free with kfree_rcu(). A concurrent tunnel_key_act() reader on the datapath may still hold the old params pointer (under rcu_read_lock_bh) and proceed to call dst_clone(¶ms->tcft_enc_metadata->dst) after the writer's dst_release has already pushed the dst's rcuref to RCUREF_DEAD.
[email protected] produced a poc which i (and Victor) verified that KASAN reports:
================================================================== BUG: KASAN: slab-use-after-free in instrument_atomic_read_write include/linux/instrumented.h:112 BUG: KASAN: slab-use-after-free in atomic_sub_return_release include/linux/atomic/atomic-instrumented.h:326 BUG: KASAN: slab-use-after-free in __rcuref_put include/linux/rcuref.h:109 BUG: KASAN: slab-use-after-free in rcuref_put include/linux/rcuref.h:173 BUG: KASAN: slab-use-after-free in dst_release+0x5b/0x370 net/core/dst.c:168 Write of size 4 at addr ffff88806158de40 by task poc/9388
CPU: 0 UID: 0 PID: 9388 Comm: poc Tainted: G W 7.1.0-rc7 #7 PREEMPT(lazy) Tainted: [W]=WARN
Hardware name: QEMU Ubuntu 25.10 PC v2 (i440FX + PIIX, + 10.1 machine, 1996), BIOS 1.16.3-debian-1.16.3-2 04/01/2014 Call Trace: <TASK> __dump_stack lib/dump_stack.c:94 dump_stack_lvl+0x100/0x190 lib/dump_stack.c:120 print_address_description mm/kasan/report.c:378 print_report+0x139/0x4ad mm/kasan/report.c:482 kasan_report+0xe4/0x1d0 mm/kasan/report.c:595 check_region_inline mm/kasan/generic.c:186 kasan_check_range+0x125/0x200 mm/kasan/generic.c:200 instrument_atomic_read_write include/linux/instrumented.h:112 atomic_sub_return_release include/linux/atomic/atomic-instrumented.h:326 __rcuref_put include/linux/rcuref.h:109 rcuref_put include/linux/rcuref.h:173 dst_release+0x5b/0x370 net/core/dst.c:168 refdst_drop include/net/dst.h:272 skb_dst_drop include/net/dst.h:284 skb_release_head_state+0x293/0x400 net/core/skbuff.c:1163 skb_release_all net/core/skbuff.c:1187 [..]
Allocated by task 9391: kasan_save_stack+0x30/0x50 mm/kasan/common.c:57 kasan_save_track+0x14/0x30 mm/kasan/common.c:78 poison_kmalloc_redzone mm/kasan/common.c:398 __kasan_kmalloc+0x9a/0xb0 mm/kasan/common.c:415 kasan_kmalloc include/linux/kasan.h:263 __do_kmalloc_node mm/slub.c:5296 __kmalloc_noprof+0x2f1/0x830 mm/slub.c:5308 kmalloc_noprof include/linux/slab.h:954 kzalloc_noprof include/linux/slab.h:1188 offload_action_alloc+0x2f/0x130 net/core/flow_offload.c:35 tcf_action_offload_add_ex+0x1ba/0x880 net/sched/act_api.c:258 tcf_action_offload_add net/sched/act_api.c:293 tcf_action_init+0x66e/0xa20 net/sched/act_api.c:1547 tcf_action_add+0xf6/0x5d0 net/sched/act_api.c:2101 [..]
Freed by task 9391: kasan_save_stack+0x30/0x50 mm/kasan/common.c:57 kasan_save_track+0x14/0x30 mm/kasan/common.c:78 kasan_save_free_info+0x3b/0x70 mm/kasan/generic.c:584 poison_slab_object mm/kasan/common.c:253 __kasan_slab_free+0x6b/0x90 mm/kasan/common.c:285 kasan_slab_free include/linux/kasan.h:235 slab_free_hook mm/slub.c:2689 slab_free mm/slub.c:6251 kfree+0x21f/0x6b0 mm/slub.c:6566 tcf_action_offload_add_ex+0x4ad/0x880 net/sched/act_api.c:284 tcf_action_offload_add net/sched/act_api.c:293 tcf_action_init+0x66e/0xa20 net/sched/act_api.c:1547 tcf_action_add+0xf6/0x5d0 net/sched/act_api.c:2101
The buggy address belongs to the object at ffff88806158de00 which belongs to the cache kmalloc-256 of size 256 The buggy address is located 64 bytes inside of freed 256-byte region [ffff88806158de00, ffff88806158df00)
The buggy address belongs to the physical page: page: refcount:0 mapcount:0 mapping:0000000000000000 index:0xffff88806158d600 pfn:0x6158c head: order:1 mapcount:0 entire_map ---truncated---
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Analysis
by VulDB Data Team • 08/10/2026
The vulnerability resides in the Linux kernel's net/sched subsystem, specifically within the act_tunnel_key implementation where a race condition leads to use-after-free behavior during tunnel key parameter management. This flaw occurs when the tunnel_key_release_params() function synchronously releases the metadata_dst of old parameters via dst_release() while deferring the actual freeing of the params structure through kfree_rcu(). The asynchronous nature of this operation creates a window where concurrent datapath readers may still hold references to the old params pointer under rcu_read_lock_bh, attempting to access dst_clone() on metadata that has already been marked for deallocation. This represents a classic race condition vulnerability where memory safety is compromised due to improper synchronization between writers and readers in a concurrent environment.
The technical implementation flaw manifests as a violation of proper resource management protocols within the kernel's networking stack. When tunnel_key_act() processes packets on the datapath, it may access parameters that have been partially deallocated by the writer thread, causing memory corruption that KASAN detects through multiple slab-use-after-free reports. The call trace shows the sequence where instrument_atomic_read_write triggers a use-after-free in atomic_sub_return_release which then propagates to __rcuref_put and ultimately dst_release, demonstrating how the improper ordering of resource deallocation creates a chain reaction of memory safety violations. This vulnerability specifically affects the kernel's traffic control framework and can be exploited through careful crafting of network packet flows that trigger concurrent access patterns.
The operational impact of this vulnerability extends beyond simple memory corruption to potentially enable privilege escalation or system instability. Attackers could leverage this race condition to execute arbitrary code within kernel space, as demonstrated by the poc provided by [email protected] that triggers KASAN reporting. The vulnerability affects systems running affected kernel versions where the net/sched subsystem handles tunnel key operations, particularly impacting network virtualization scenarios and traffic control policies that utilize tunneling mechanisms. According to CWE standards, this maps directly to CWE-416: Use After Free, with elements of CWE-362: Concurrent Execution using Shared Resource with Improper Synchronization, making it a critical security concern for network infrastructure components.
Mitigation strategies should focus on ensuring proper synchronization between the writer and reader paths in the tunnel key parameter management system. The fix requires reordering resource deallocation operations to ensure that dst_release() occurs only after all potential readers have completed their access to the metadata, potentially through enhanced RCU callback mechanisms or by deferring the entire parameter structure release until all readers have been guaranteed to have completed their work. Organizations should prioritize kernel updates to versions containing the fix, while network administrators should monitor for unusual traffic patterns that might indicate exploitation attempts. Additional defensive measures include implementing stricter memory access controls and monitoring for KASAN reports in production systems, as this vulnerability aligns with ATT&CK technique T1068: Exploitation for Privilege Escalation through kernel-level attacks targeting system resource management components.