CVE-2025-21731: nbd: don't allow reconnect after disconnect
First published: Thu Feb 27 2025(Updated: )
In the Linux kernel, the following vulnerability has been resolved: nbd: don't allow reconnect after disconnect Following process can cause nbd_config UAF: 1) grab nbd_config temporarily; 2) nbd_genl_disconnect() flush all recv_work() and release the initial reference: nbd_genl_disconnect nbd_disconnect_and_put nbd_disconnect flush_workqueue(nbd->recv_workq) if (test_and_clear_bit(NBD_RT_HAS_CONFIG_REF, ...)) nbd_config_put -> due to step 1), reference is still not zero 3) nbd_genl_reconfigure() queue recv_work() again; nbd_genl_reconfigure config = nbd_get_config_unlocked(nbd) if (!config) -> succeed if (!test_bit(NBD_RT_BOUND, ...)) -> succeed nbd_reconnect_socket queue_work(nbd->recv_workq, &args->work) 4) step 1) release the reference; 5) Finially, recv_work() will trigger UAF: recv_work nbd_config_put(nbd) -> nbd_config is freed atomic_dec(&config->recv_threads) -> UAF Fix the problem by clearing NBD_RT_BOUND in nbd_genl_disconnect(), so that nbd_genl_reconfigure() will fail.
Credit: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
| Affected Software | Affected Version | How to fix |
|---|---|---|
| Linux Kernel | ||
| Linux Kernel | >=4.12<5.4.291 | |
| Linux Kernel | >=5.5<5.10.235 | |
| Linux Kernel | >=5.11<5.15.179 | |
| Linux Kernel | >=5.16<6.1.129 | |
| Linux Kernel | >=6.2<6.6.76 | |
| Linux Kernel | >=6.7<6.12.13 | |
| Linux Kernel | >=6.13<6.13.2 |
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Reference Links
- https://git.kernel.org/stable/c/844b8cdc681612ff24df62cdefddeab5772fadf1
- https://git.kernel.org/stable/c/9793bd5ae4bdbdb2dde401a3cab94a6bfd05e302
- https://git.kernel.org/stable/c/a8ee6ecde2b7bfb58c8a3afe8a9d2b848f580739
- https://git.kernel.org/stable/c/d208d2c52b652913b5eefc8ca434b0d6b757f68f
- https://git.kernel.org/stable/c/e7343fa33751cb07c1c56b666bf37cfca357130e
- https://git.kernel.org/stable/c/e70a578487a47d7cf058904141e586684d1c3381
- https://git.kernel.org/stable/c/6bef6222a3f6c7adb6396f77f25a3579d821b09a
- https://git.kernel.org/stable/c/e3be8862d73cac833e0fb7602636c19c6cb94b11
Frequently Asked Questions
What is the severity of CVE-2025-21731?
CVE-2025-21731 is classified as a moderate severity vulnerability in the Linux kernel.
How do I fix CVE-2025-21731?
To mitigate CVE-2025-21731, it is recommended to update to the latest version of the Linux kernel where the vulnerability has been patched.
What components are affected by CVE-2025-21731?
CVE-2025-21731 primarily affects the nbd (Network Block Device) component of the Linux kernel.
What type of vulnerability is CVE-2025-21731?
CVE-2025-21731 is a use-after-free (UAF) vulnerability that can lead to potential arbitrary code execution.
Can CVE-2025-21731 be exploited remotely?
Yes, CVE-2025-21731 could potentially be exploited remotely if the affected nbd service is improperly configured.
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