Linux Kernel up to 6.16.1 mm/slub.c kvmalloc_array file descriptor consumption

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Summaryinfo

A vulnerability classified as critical was found in Linux Kernel up to 6.16.1. Affected is the function kvmalloc_array of the file mm/slub.c. The manipulation results in file descriptor consumption. This vulnerability is reported as CVE-2025-39756. No exploit exists. Upgrading the affected component is advised.

Detailsinfo

A vulnerability, which was classified as critical, was found in Linux Kernel up to 6.16.1. Affected is the function kvmalloc_array of the file mm/slub.c. The manipulation with an unknown input leads to a file descriptor consumption vulnerability. CWE is classifying the issue as CWE-769. This entry has been deprecated because it was a duplicate of CWE-774. All content has been transferred to CWE-774. This is going to have an impact on availability. CVE summarizes:

In the Linux kernel, the following vulnerability has been resolved: fs: Prevent file descriptor table allocations exceeding INT_MAX When sysctl_nr_open is set to a very high value (for example, 1073741816 as set by systemd), processes attempting to use file descriptors near the limit can trigger massive memory allocation attempts that exceed INT_MAX, resulting in a WARNING in mm/slub.c: WARNING: CPU: 0 PID: 44 at mm/slub.c:5027 __kvmalloc_node_noprof+0x21a/0x288 This happens because kvmalloc_array() and kvmalloc() check if the requested size exceeds INT_MAX and emit a warning when the allocation is not flagged with __GFP_NOWARN. Specifically, when nr_open is set to 1073741816 (0x3ffffff8) and a process calls dup2(oldfd, 1073741880), the kernel attempts to allocate: - File descriptor array: 1073741880 * 8 bytes = 8,589,935,040 bytes - Multiple bitmaps: ~400MB - Total allocation size: > 8GB (exceeding INT_MAX = 2,147,483,647) Reproducer: 1. Set /proc/sys/fs/nr_open to 1073741816: # echo 1073741816 > /proc/sys/fs/nr_open 2. Run a program that uses a high file descriptor: #include <unistd.h> #include <sys/resource.h> int main() { struct rlimit rlim = {1073741824, 1073741824}; setrlimit(RLIMIT_NOFILE, &rlim); dup2(2, 1073741880); // Triggers the warning return 0; } 3. Observe WARNING in dmesg at mm/slub.c:5027 systemd commit a8b627a introduced automatic bumping of fs.nr_open to the maximum possible value. The rationale was that systems with memory control groups (memcg) no longer need separate file descriptor limits since memory is properly accounted. However, this change overlooked that: 1. The kernel's allocation functions still enforce INT_MAX as a maximum size regardless of memcg accounting 2. Programs and tests that legitimately test file descriptor limits can inadvertently trigger massive allocations 3. The resulting allocations (>8GB) are impractical and will always fail systemd's algorithm starts with INT_MAX and keeps halving the value until the kernel accepts it. On most systems, this results in nr_open being set to 1073741816 (0x3ffffff8), which is just under 1GB of file descriptors. While processes rarely use file descriptors near this limit in normal operation, certain selftests (like tools/testing/selftests/core/unshare_test.c) and programs that test file descriptor limits can trigger this issue. Fix this by adding a check in alloc_fdtable() to ensure the requested allocation size does not exceed INT_MAX. This causes the operation to fail with -EMFILE instead of triggering a kernel warning and avoids the impractical >8GB memory allocation request.

The advisory is shared for download at git.kernel.org. This vulnerability is traded as CVE-2025-39756 since 04/16/2025. There are known technical details, but no exploit is available.

The vulnerability scanner Nessus provides a plugin with the ID 264737 (Linux Distros Unpatched Vulnerability : CVE-2025-39756), which helps to determine the existence of the flaw in a target environment.

Upgrading to version 5.4.297, 5.10.241, 5.15.190, 6.1.149, 6.6.103, 6.12.43, 6.15.11, 6.16.2 or 6.17-rc1 eliminates this vulnerability. Applying a patch 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 (264737), EUVD (EUVD-2025-28956) and CERT Bund (WID-SEC-2025-2040). Once again VulDB remains the best source for vulnerability data.

Affected

  • Google Container-Optimized OS
  • Debian Linux
  • Google Cloud Platform
  • Amazon Linux 2
  • Red Hat Enterprise Linux
  • Fedora Linux
  • Ubuntu Linux
  • SUSE Linux
  • Oracle Linux
  • SUSE openSUSE
  • RESF Rocky Linux
  • Open Source Linux Kernel
  • Proxmox Virtual Environment
  • Proxmox Backup Server
  • Dell Secure Connect Gateway
  • IBM QRadar SIEM

Productinfo

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Vendor

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Version

License

Website

CPE 2.3info

CPE 2.2info

CVSSv4info

VulDB Vector: 🔒
VulDB Reliability: 🔍

CVSSv3info

VulDB Meta Base Score: 5.6
VulDB Meta Temp Score: 5.5

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

NVD Base Score: 5.5
NVD Vector: 🔒

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: Partially
Local: Yes
Remote: Partially

Availability: 🔒
Status: Not defined

EPSS Score: 🔒
EPSS Percentile: 🔒

Price Prediction: 🔍
Current Price Estimation: 🔒

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Nessus ID: 264737
Nessus Name: Linux Distros Unpatched Vulnerability : CVE-2025-39756

Threat Intelligenceinfo

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

Countermeasuresinfo

Recommended: Upgrade
Status: 🔍

0-Day Time: 🔒

Upgrade: Kernel 5.4.297/5.10.241/5.15.190/6.1.149/6.6.103/6.12.43/6.15.11/6.16.2/6.17-rc1
Patch: git.kernel.org

Timelineinfo

04/16/2025 CVE reserved
09/11/2025 +148 days Advisory disclosed
09/11/2025 +0 days VulDB entry created
01/10/2026 +121 days VulDB entry last update

Sourcesinfo

Vendor: kernel.org

Advisory: git.kernel.org
Status: Confirmed

CVE: CVE-2025-39756 (🔒)
GCVE (CVE): GCVE-0-2025-39756
GCVE (VulDB): GCVE-100-323652
EUVD: 🔒
CERT Bund: WID-SEC-2025-2040 - Linux Kernel: Mehrere Schwachstellen erm&ouml;glichen Denial of Service

Entryinfo

Created: 09/11/2025 19:30
Updated: 01/10/2026 09:33
Changes: 09/11/2025 19:30 (58), 09/12/2025 18:13 (7), 09/14/2025 22:06 (2), 11/08/2025 01:51 (1), 11/16/2025 00:09 (1), 01/09/2026 21:03 (11), 01/10/2026 09:33 (1)
Complete: 🔍
Cache ID: 216::103

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