CVE-2025-22024 in Linux
Summary
by MITRE • 04/16/2025
In the Linux kernel, the following vulnerability has been resolved:
nfsd: fix management of listener transports
Currently, when no active threads are running, a root user using nfsdctl command can try to remove a particular listener from the list of previously added ones, then start the server by increasing the number of threads, it leads to the following problem:
[ 158.835354] refcount_t: addition on 0; use-after-free.
[ 158.835603] WARNING: CPU: 2 PID: 9145 at lib/refcount.c:25 refcount_warn_saturate+0x160/0x1a0
[ 158.836017] Modules linked in: rpcrdma rdma_cm iw_cm ib_cm ib_core nfsd auth_rpcgss nfs_acl lockd grace overlay isofs uinput snd_seq_dummy snd_hrtimer nft_fib_inet nft_fib_ipv4 nft_fib_ipv6 nft_fib nft_reject_inet nf_reject_ipv4 nf_reject_ipv6 nft_reject nft_ct nft_chain_nat nf_nat nf_conntrack nf_defrag_ipv6 nf_defrag_ipv4 rfkill ip_set nf_tables qrtr sunrpc vfat fat uvcvideo videobuf2_vmalloc videobuf2_memops uvc videobuf2_v4l2 videodev videobuf2_common snd_hda_codec_generic mc e1000e snd_hda_intel snd_intel_dspcfg snd_hda_codec snd_hda_core snd_hwdep snd_seq snd_seq_device snd_pcm snd_timer snd soundcore sg loop dm_multipath dm_mod nfnetlink vsock_loopback vmw_vsock_virtio_transport_common vmw_vsock_vmci_transport vmw_vmci vsock xfs libcrc32c crct10dif_ce ghash_ce vmwgfx sha2_ce sha256_arm64 sr_mod sha1_ce cdrom nvme drm_client_lib drm_ttm_helper ttm nvme_core drm_kms_helper nvme_auth drm fuse
[ 158.840093] CPU: 2 UID: 0 PID: 9145 Comm: nfsd Kdump: loaded Tainted: G B W 6.13.0-rc6+ #7
[ 158.840624] Tainted: [B]=BAD_PAGE, [W]=WARN
[ 158.840802] Hardware name: VMware, Inc. VMware20,1/VBSA, BIOS VMW201.00V.24006586.BA64.2406042154 06/04/2024
[ 158.841220] pstate: 61400005 (nZCv daif +PAN -UAO -TCO +DIT -SSBS BTYPE=--)
[ 158.841563] pc : refcount_warn_saturate+0x160/0x1a0
[ 158.841780] lr : refcount_warn_saturate+0x160/0x1a0
[ 158.842000] sp : ffff800089be7d80
[ 158.842147] x29: ffff800089be7d80 x28: ffff00008e68c148 x27: ffff00008e68c148
[ 158.842492] x26: ffff0002e3b5c000 x25: ffff600011cd1829 x24: ffff00008653c010
[ 158.842832] x23: ffff00008653c000 x22: 1fffe00011cd1829 x21: ffff00008653c028
[ 158.843175] x20: 0000000000000002 x19: ffff00008653c010 x18: 0000000000000000
[ 158.843505] x17: 0000000000000000 x16: 0000000000000000 x15: 0000000000000000
[ 158.843836] x14: 0000000000000000 x13: 0000000000000001 x12: ffff600050a26493
[ 158.844143] x11: 1fffe00050a26492 x10: ffff600050a26492 x9 : dfff800000000000
[ 158.844475] x8 : 00009fffaf5d9b6e x7 : ffff000285132493 x6 : 0000000000000001
[ 158.844823] x5 : ffff000285132490 x4 : ffff600050a26493 x3 : ffff8000805e72bc
[ 158.845174] x2 : 0000000000000000 x1 : 0000000000000000 x0 : ffff000098588000
[ 158.845528] Call trace:
[ 158.845658] refcount_warn_saturate+0x160/0x1a0 (P)
[ 158.845894] svc_recv+0x58c/0x680 [sunrpc]
[ 158.846183] nfsd+0x1fc/0x348 [nfsd]
[ 158.846390] kthread+0x274/0x2f8
[ 158.846546] ret_from_fork+0x10/0x20
[ 158.846714] ---[ end trace 0000000000000000 ]---
nfsd_nl_listener_set_doit() would manipulate the list of transports of server's sv_permsocks and close the specified listener but the other list of transports (server's sp_xprts list) would not be changed leading to the problem above.
Instead, determined if the nfsdctl is trying to remove a listener, in which case, delete all the existing listener transports and re-create all-but-the-removed ones.
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Analysis
by VulDB Data Team • 03/16/2026
The vulnerability described in CVE-2025-22024 resides within the Linux kernel's Network File System Daemon (nfsd) subsystem, specifically in how it manages listener transports during server configuration changes. This flaw manifests when a root user executes the nfsdctl command to remove a particular listener from the list of previously added ones, followed by starting the NFS server with an increased number of threads. The issue stems from improper synchronization and management of transport lists, leading to a use-after-free condition that can result in system instability or potential exploitation. The error message indicates a refcount_t addition on zero, which is a classic symptom of attempting to increment a reference count on a freed object, signaling a critical memory management failure.
The technical root cause involves two distinct transport lists within the nfsd server structure: sv_permsocks and sp_xprts. When nfsdctl removes a listener, it modifies the sv_permsocks list by closing the specified listener, but fails to update the sp_xprts list accordingly. This inconsistency creates a scenario where the server attempts to reference transport objects that have already been freed, leading to the kernel panic and warning messages observed in the stack trace. The call trace shows the error propagating through svc_recv in the sunrpc module, indicating that the issue occurs during network request processing after the transport objects have been improperly deallocated. This type of vulnerability aligns with CWE-415, which describes double free conditions, and CWE-416, which covers use-after-free errors, both of which are fundamental memory safety issues in kernel space.
The operational impact of this vulnerability is significant for systems running NFS services, particularly in environments where root privileges are available to untrusted users or where automated management scripts might inadvertently trigger the problematic sequence. A successful exploitation could lead to denial of service, system crashes, or potentially privilege escalation depending on the broader context of the system's security posture. The vulnerability affects systems using the Linux kernel version 6.13.0-rc6 and later, making it relevant to both development and production environments that rely on NFS services. The issue is particularly concerning because it requires only root privileges to trigger, making it accessible to users with administrative access and potentially exploitable in containerized environments or shared hosting scenarios.
Mitigation strategies for this vulnerability include immediate patching of the Linux kernel to the fixed version that properly synchronizes both transport lists during listener removal operations. Administrators should also implement strict access controls to prevent unauthorized root-level execution of nfsdctl commands, particularly in multi-tenant or shared environments. Monitoring systems should be configured to detect unusual patterns in NFS service management, such as rapid succession of listener removal and thread start operations. Additionally, the use of kernel lockdown mechanisms or secure boot configurations can help prevent exploitation by limiting the ability to load modified kernel modules. Organizations should also consider implementing network segmentation to limit access to NFS services and regularly audit NFS configurations to ensure that listener management operations are performed safely. This vulnerability demonstrates the importance of careful memory management in kernel space and highlights the need for thorough testing of configuration change workflows in critical system components. The fix implemented addresses the core issue by ensuring that when a listener is removed, all existing listener transports are deleted and recreated excluding the removed one, thereby maintaining consistency between the two transport lists and preventing the use-after-free condition that was previously possible.