CVE-2026-97583 in Linux
Summary
by MITRE • 09/25/2026
In the Linux kernel, the following vulnerability has been resolved:
afs: Clear stale peer app data after address list changes
afs_fs_probe_fileserver() fetches the current endpoint state under server->fs_lock, but leaves old_alist as NULL. Consequently, afs_set_peer_appdata() treats every address list replacement as initial setup and only binds the new peers; it never unbinds peers removed from the old list.
An address refresh can therefore proceed as follows. CPU 0 replaces server S's list and drops Pold without clearing Pold->app_data. The server destroyer then clears only S's current peers and lets S reach its RCU callback. After the callback frees S, CPU 1 handles a callback through an RxRPC connection that still pins Pold, reads Pold->app_data, and calls afs_use_server() on the freed object.
KASAN reported:
BUG: KASAN: slab-use-after-free in afs_find_server+0x3c/0xa0 Read of size 4 at addr ffff8881013e1af0 by task krxrpcio/7001/74 Call Trace: afs_find_server+0x3c/0xa0 afs_rx_new_call+0x15c/0x390 rxrpc_new_incoming_call+0x97c/0x1730 rxrpc_input_packet.constprop.0+0xd03/0xec0 rxrpc_io_thread+0x967/0x1640 Allocated by task 93: afs_lookup_server+0x1a7/0x14c0 afs_alloc_server_list+0x43f/0xb60 afs_create_volume+0x923/0x1490 afs_get_tree+0x1c6/0x10a0 Freed by task 0: kfree+0x131/0x3c0 rcu_core+0x50a/0x1850 Last potentially related work creation: __call_rcu_common.constprop.0+0x71/0xa10 afs_put_server+0x213/0x2b0
Preserve old->addresses for the peer app-data update so that removed peers are cleared before the endpoint state is replaced. Also advance both cursors when the old and new lists share a peer; activating the old/new comparison without this would otherwise loop forever on the shared entry.
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Analysis
by VulDB Data Team • 09/25/2026
The vulnerability identified in the Linux kernel's AFS filesystem component represents a critical use-after-free condition arising from improper lifecycle management of network endpoint structures during address list updates. The core technical flaw resides within the afs_fs_probe_fileserver function, which is responsible for fetching and updating the current endpoint state under server lock protection. When an address refresh occurs, the system replaces the existing address list with a new one but fails to properly handle the cleanup of peers that are no longer present in the updated configuration. Specifically, the variable representing the old address list remains null or improperly managed during this transition, causing afs_set_peer_appdata to treat every replacement as an initial setup phase rather than a state update. Consequently, while new peers bound to fresh addresses are correctly initialized, any peer removed from the server's address list is never unbound or cleared of its associated application data. This oversight leaves stale references alive in memory even after the underlying server object has been deallocated.
The operational impact of this flaw manifests as a severe stability and security risk due to use-after-free conditions that can be triggered by normal network operations such as callback handling or packet processing. When an address refresh proceeds, CPU 0 may replace the server's peer list and drop old peers without clearing their app_data structures. Subsequently, the server destroyer clears only the current peers of the server object and allows it to reach its RCU (Read-Copy-Update) callback phase, at which point the memory for the server structure is freed. However, if CPU 1 simultaneously handles a network callback through an RxRPC connection that still holds a reference pinning one of these old peer structures, it will attempt to read from Pold->app_data. Since this data belongs to a now-freed object, the kernel executes code against invalid memory addresses. This scenario was confirmed by Kernel Address Sanitizer (KASAN) reports indicating slab-use-after-free errors in afs_find_server, triggered during incoming call processing via rxrpc_new_incoming_call and subsequent packet input handling. Such conditions can lead to system crashes, data corruption, or potentially exploitable arbitrary read/write primitives if an attacker can influence the timing of address refreshes and concurrent network callbacks.
From a vulnerability classification perspective, this issue aligns with CWE-416: Use After Free, as it involves accessing memory after it has been freed due to incorrect pointer management. The attack vector leverages race conditions inherent in multi-core systems where lock granularity or cleanup logic fails to synchronize the lifecycle of dependent objects like peer structures and their parent server objects. In terms of MITRE ATT&CK mapping, this vulnerability facilitates techniques related to Execution via Client Binary Proxy Abuse or potentially Defense Evasion through memory corruption if exploited for code execution, though its primary classification remains a reliability issue exploitable for denial-of-service conditions. The root cause is not merely a logic error but a failure in maintaining consistent state across concurrent operations involving network stack components and filesystem server management layers.
To mitigate this vulnerability, the kernel developers implemented a fix that preserves references to old addresses during peer app-data updates, ensuring that removed peers are explicitly cleared before the endpoint state is replaced. This change prevents stale data from persisting after deallocation. Additionally, the logic for comparing old and new address lists was adjusted so that cursors advance correctly when both lists share common peers, preventing infinite loops in comparison routines that could otherwise cause kernel hangs or excessive CPU consumption. Administrators should ensure their systems are updated with patches addressing this specific AFS subsystem flaw to prevent potential crashes during high-frequency network operations involving volume mounts and server address changes. Regular patching of the Linux kernel is essential as these low-level memory management errors can have cascading effects on system stability, particularly in environments relying heavily on distributed filesystems like AFS for data access.