Linux Kernel up to 6.12.43/6.16.3/6.17-rc2 netfs write_iter null pointer dereference

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6.6$0-$5k0.00

Summaryinfo

A vulnerability classified as critical has been found in Linux Kernel up to 6.12.43/6.16.3/6.17-rc2. This affects the function write_iter of the component netfs. This manipulation causes null pointer dereference. This vulnerability is handled as CVE-2025-39723. There is not any exploit available. It is recommended to upgrade the affected component.

Detailsinfo

A vulnerability has been found in Linux Kernel up to 6.12.43/6.16.3/6.17-rc2 and classified as critical. Affected by this vulnerability is the function write_iter of the component netfs. The manipulation with an unknown input leads to a null pointer dereference vulnerability. The CWE definition for the vulnerability is CWE-476. A NULL pointer dereference occurs when the application dereferences a pointer that it expects to be valid, but is NULL, typically causing a crash or exit. As an impact it is known to affect availability. The summary by CVE is:

In the Linux kernel, the following vulnerability has been resolved: netfs: Fix unbuffered write error handling If all the subrequests in an unbuffered write stream fail, the subrequest collector doesn't update the stream->transferred value and it retains its initial LONG_MAX value. Unfortunately, if all active streams fail, then we take the smallest value of { LONG_MAX, LONG_MAX, ... } as the value to set in wreq->transferred - which is then returned from ->write_iter(). LONG_MAX was chosen as the initial value so that all the streams can be quickly assessed by taking the smallest value of all stream->transferred - but this only works if we've set any of them. Fix this by adding a flag to indicate whether the value in stream->transferred is valid and checking that when we integrate the values. stream->transferred can then be initialised to zero. This was found by running the generic/750 xfstest against cifs with cache=none. It splices data to the target file. Once (if) it has used up all the available scratch space, the writes start failing with ENOSPC. This causes ->write_iter() to fail. However, it was returning wreq->transferred, i.e. LONG_MAX, rather than an error (because it thought the amount transferred was non-zero) and iter_file_splice_write() would then try to clean up that amount of pipe bufferage - leading to an oops when it overran. The kernel log showed: CIFS: VFS: Send error in write = -28 followed by: BUG: kernel NULL pointer dereference, address: 0000000000000008 with: RIP: 0010:iter_file_splice_write+0x3a4/0x520 do_splice+0x197/0x4e0 or: RIP: 0010:pipe_buf_release (include/linux/pipe_fs_i.h:282) iter_file_splice_write (fs/splice.c:755) Also put a warning check into splice to announce if ->write_iter() returned that it had written more than it was asked to.

It is possible to read the advisory at git.kernel.org. This vulnerability is known as CVE-2025-39723 since 04/16/2025. Technical details of the vulnerability are known, but there is no available exploit.

The vulnerability scanner Nessus provides a plugin with the ID 261603 (Linux Distros Unpatched Vulnerability : CVE-2025-39723), which helps to determine the existence of the flaw in a target environment.

Upgrading to version 6.12.44, 6.16.4 or 6.17-rc3 eliminates this vulnerability. Applying the patch f08c80af3c9a9849cd178b4843b7c01d103506a1/387164a2b97e1f5404c6d0049a7409bac7d2bc5b/a3de58b12ce074ec05b8741fa28d62ccb1070468 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 (261603) and CERT Bund (WID-SEC-2025-1988). Be aware that VulDB is the high quality source for vulnerability data.

Affected

  • Debian Linux
  • Google Cloud Platform
  • Amazon Linux 2
  • Red Hat Enterprise Linux
  • Ubuntu Linux
  • SUSE Linux
  • Oracle Linux
  • NetApp FAS
  • NetApp AFF
  • NetApp ActiveIQ Unified Manager
  • SUSE openSUSE
  • RESF Rocky Linux
  • Open Source Linux Kernel
  • Microsoft Azure
  • Dell Secure Connect Gateway
  • IBM QRadar SIEM
  • IBM Security Verify Access
  • Dell NetWorker

Productinfo

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CPE 2.3info

CPE 2.2info

CVSSv4info

VulDB Vector: 🔒
VulDB Reliability: 🔍

CVSSv3info

VulDB Meta Base Score: 6.7
VulDB Meta Temp Score: 6.6

VulDB Base Score: 5.7
VulDB Temp Score: 5.5
VulDB Vector: 🔒
VulDB Reliability: 🔍

NVD Base Score: 7.8
NVD Vector: 🔒

CVSSv2info

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

Exploitinginfo

Class: Null pointer dereference
CWE: CWE-476 / CWE-404
CAPEC: 🔒
ATT&CK: 🔒

Physical: Partially
Local: Yes
Remote: Partially

Availability: 🔒
Status: Not defined

EPSS Score: 🔒
EPSS Percentile: 🔒

Price Prediction: 🔍
Current Price Estimation: 🔒

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Nessus ID: 261603
Nessus Name: Linux Distros Unpatched Vulnerability : CVE-2025-39723

Threat Intelligenceinfo

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

Countermeasuresinfo

Recommended: Upgrade
Status: 🔍

0-Day Time: 🔒

Upgrade: Kernel 6.12.44/6.16.4/6.17-rc3
Patch: f08c80af3c9a9849cd178b4843b7c01d103506a1/387164a2b97e1f5404c6d0049a7409bac7d2bc5b/a3de58b12ce074ec05b8741fa28d62ccb1070468

Timelineinfo

04/16/2025 CVE reserved
09/05/2025 +142 days Advisory disclosed
09/05/2025 +0 days VulDB entry created
02/09/2026 +157 days VulDB entry last update

Sourcesinfo

Vendor: kernel.org

Advisory: git.kernel.org
Status: Confirmed

CVE: CVE-2025-39723 (🔒)
GCVE (CVE): GCVE-0-2025-39723
GCVE (VulDB): GCVE-100-322951
CERT Bund: WID-SEC-2025-1988 - Linux Kernel: Mehrere Schwachstellen ermöglichen Denial of Service

Entryinfo

Created: 09/05/2025 22:16
Updated: 02/09/2026 21:00
Changes: 09/05/2025 22:16 (59), 09/07/2025 13:19 (2), 11/26/2025 23:24 (11), 11/27/2025 23:29 (7), 01/03/2026 15:02 (1), 01/25/2026 12:28 (1), 02/09/2026 21:00 (1)
Complete: 🔍
Cache ID: 216::103

Be aware that VulDB is the high quality source for vulnerability data.

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