Linux Kernel up to 6.17.3 request_wait_answer file descriptor consumption

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3.4$0-$5k0.00

Summaryinfo

A vulnerability was found in Linux Kernel up to 6.17.3 and classified as critical. This vulnerability affects the function request_wait_answer. Executing a manipulation can lead to file descriptor consumption. This vulnerability is tracked as CVE-2025-40220. No exploit exists. It is suggested to upgrade the affected component.

Detailsinfo

A vulnerability has been found in Linux Kernel up to 6.17.3 and classified as problematic. This vulnerability affects the function request_wait_answer. The manipulation with an unknown input leads to a file descriptor consumption vulnerability. The CWE definition for the vulnerability is CWE-769. This entry has been deprecated because it was a duplicate of CWE-774. All content has been transferred to CWE-774. As an impact it is known to affect availability. CVE summarizes:

In the Linux kernel, the following vulnerability has been resolved: fuse: fix livelock in synchronous file put from fuseblk workers I observed a hang when running generic/323 against a fuseblk server. This test opens a file, initiates a lot of AIO writes to that file descriptor, and closes the file descriptor before the writes complete. Unsurprisingly, the AIO exerciser threads are mostly stuck waiting for responses from the fuseblk server: # cat /proc/372265/task/372313/stack [<0>] request_wait_answer+0x1fe/0x2a0 [fuse] [<0>] __fuse_simple_request+0xd3/0x2b0 [fuse] [<0>] fuse_do_getattr+0xfc/0x1f0 [fuse] [<0>] fuse_file_read_iter+0xbe/0x1c0 [fuse] [<0>] aio_read+0x130/0x1e0 [<0>] io_submit_one+0x542/0x860 [<0>] __x64_sys_io_submit+0x98/0x1a0 [<0>] do_syscall_64+0x37/0xf0 [<0>] entry_SYSCALL_64_after_hwframe+0x4b/0x53 But the /weird/ part is that the fuseblk server threads are waiting for responses from itself: # cat /proc/372210/task/372232/stack [<0>] request_wait_answer+0x1fe/0x2a0 [fuse] [<0>] __fuse_simple_request+0xd3/0x2b0 [fuse] [<0>] fuse_file_put+0x9a/0xd0 [fuse] [<0>] fuse_release+0x36/0x50 [fuse] [<0>] __fput+0xec/0x2b0 [<0>] task_work_run+0x55/0x90 [<0>] syscall_exit_to_user_mode+0xe9/0x100 [<0>] do_syscall_64+0x43/0xf0 [<0>] entry_SYSCALL_64_after_hwframe+0x4b/0x53 The fuseblk server is fuse2fs so there's nothing all that exciting in the server itself. So why is the fuse server calling fuse_file_put? The commit message for the fstest sheds some light on that: "By closing the file descriptor before calling io_destroy, you pretty much guarantee that the last put on the ioctx will be done in interrupt context (during I/O completion). Aha. AIO fgets a new struct file from the fd when it queues the ioctx. The completion of the FUSE_WRITE command from userspace causes the fuse server to call the AIO completion function. The completion puts the struct file, queuing a delayed fput to the fuse server task. When the fuse server task returns to userspace, it has to run the delayed fput, which in the case of a fuseblk server, it does synchronously. Sending the FUSE_RELEASE command sychronously from fuse server threads is a bad idea because a client program can initiate enough simultaneous AIOs such that all the fuse server threads end up in delayed_fput, and now there aren't any threads left to handle the queued fuse commands. Fix this by only using asynchronous fputs when closing files, and leave a comment explaining why.

The advisory is available at git.kernel.org. This vulnerability was named CVE-2025-40220 since 04/16/2025. Technical details are known, but there is no available exploit.

The vulnerability scanner Nessus provides a plugin with the ID 277496 (Linux Distros Unpatched Vulnerability : CVE-2025-40220), which helps to determine the existence of the flaw in a target environment.

Upgrading to version 5.10.246, 5.15.196, 6.1.158, 6.6.115, 6.12.54 or 6.17.4 eliminates this vulnerability. Applying the patch 548e1f2bac1d4df91a6138f26bb4ab00323fd948/cfd1aa3e2b71f3327cb373c45a897c9028c62b35/83b375c6efef69b1066ad2d79601221e7892745a/bfd17b6138df0122a95989457d8e18ce0b86165e/b26923512dbe57ae4917bafd31396d22a9d1691a/f19a1390af448d9e193c08e28ea5f727bf3c3049/26e5c67deb2e1f42a951f022fdf5b9f7eb747b01 is able to eliminate this problem. The bugfix is ready for download at git.kernel.org. The best possible mitigation is suggested to be upgrading to the latest version.

The vulnerability is also documented in the databases at Tenable (277496) and CERT Bund (WID-SEC-2025-2747). If you want to get best quality of vulnerability data, you may have to visit VulDB.

Affected

  • Debian Linux
  • Google Cloud Platform
  • Amazon Linux 2
  • Red Hat Enterprise Linux
  • Ubuntu Linux
  • SUSE Linux
  • Oracle Linux
  • SUSE openSUSE
  • Open Source Linux Kernel
  • RESF Rocky Linux
  • Microsoft Azure Linux

Productinfo

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Version

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Website

CPE 2.3info

CPE 2.2info

CVSSv4info

VulDB Vector: 🔒
VulDB Reliability: 🔍

CVSSv3info

VulDB Meta Base Score: 3.5
VulDB Meta Temp Score: 3.4

VulDB Base Score: 3.5
VulDB Temp Score: 3.4
VulDB Vector: 🔒
VulDB Reliability: 🔍

CVSSv2info

AVACAuCIA
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VulDB Base Score: 🔒
VulDB Temp Score: 🔒
VulDB Reliability: 🔍

Exploitinginfo

Class: File descriptor consumption
CWE: CWE-769 / CWE-400 / CWE-404
CAPEC: 🔒
ATT&CK: 🔒

Physical: No
Local: No
Remote: Partially

Availability: 🔒
Status: Not defined

EPSS Score: 🔒
EPSS Percentile: 🔒

Price Prediction: 🔍
Current Price Estimation: 🔒

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Nessus ID: 277496
Nessus Name: Linux Distros Unpatched Vulnerability : CVE-2025-40220

Threat Intelligenceinfo

Interest: 🔍
Active Actors: 🔍
Active APT Groups: 🔍

Countermeasuresinfo

Recommended: Upgrade
Status: 🔍

0-Day Time: 🔒

Upgrade: Kernel 5.10.246/5.15.196/6.1.158/6.6.115/6.12.54/6.17.4
Patch: 548e1f2bac1d4df91a6138f26bb4ab00323fd948/cfd1aa3e2b71f3327cb373c45a897c9028c62b35/83b375c6efef69b1066ad2d79601221e7892745a/bfd17b6138df0122a95989457d8e18ce0b86165e/b26923512dbe57ae4917bafd31396d22a9d1691a/f19a1390af448d9e193c08e28ea5f727bf3c3049/26e5c67deb2e1f42a951f022fdf5b9f7eb747b01

Timelineinfo

04/16/2025 CVE reserved
12/04/2025 +232 days Advisory disclosed
12/04/2025 +0 days VulDB entry created
02/23/2026 +81 days VulDB entry last update

Sourcesinfo

Vendor: kernel.org

Advisory: git.kernel.org
Status: Confirmed

CVE: CVE-2025-40220 (🔒)
GCVE (CVE): GCVE-0-2025-40220
GCVE (VulDB): GCVE-100-334282
CERT Bund: WID-SEC-2025-2747 - Linux Kernel: Mehrere Schwachstellen erm&ouml;glichen Denial of Service

Entryinfo

Created: 12/04/2025 17:28
Updated: 02/23/2026 13:45
Changes: 12/04/2025 17:28 (58), 12/06/2025 07:58 (1), 12/06/2025 20:17 (2), 01/05/2026 00:31 (7), 02/23/2026 13:45 (1)
Complete: 🔍
Cache ID: 216::103

If you want to get best quality of vulnerability data, you may have to visit VulDB.

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