CVE-2025-39756

MEDIUM EPSS 6.3%
Published Sep 11, 20259mo ago · Modified Jun 17, 20262w ago
5.5 CVSS 3.1
Medium
Find Similar
Published Sep 11, 2025 9mo ago
Last Modified Jun 17, 2026 2w ago

Description

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.

CVSS Details

Base Score
5.5
Exploitability
1.8
Impact
3.6
Vector string
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
Attack Vector Local
Attack Complexity Low
Privileges Required Low
User Interaction None
Scope Unchanged
Confidentiality None
Integrity None
Availability High

Threat Intelligence

EPSS Exploit Probability
6.3% percentile
Exploit & Patch Status
No Known Exploit
Patch Available

Weaknesses 1

CWE-401

Affected Products 9

VendorProductVersionRange
linuxlinux_kernel*≥2.6.25  –  <5.4.297
linuxlinux_kernel*≥5.5  –  <5.10.241
linuxlinux_kernel*≥5.11  –  <5.15.190
linuxlinux_kernel*≥5.16  –  <6.1.149
linuxlinux_kernel*≥6.2  –  <6.6.103
linuxlinux_kernel*≥6.7  –  <6.12.43
linuxlinux_kernel*≥6.13  –  <6.15.11
linuxlinux_kernel*≥6.16  –  <6.16.2
debiandebian_linux11.0any

References 13

  • cert-portal.siemens.com https://cert-portal.siemens.com/productcert/html/ssa-032379.html
  • cert-portal.siemens.com https://cert-portal.siemens.com/productcert/html/ssa-082556.html
  • git.kernel.org https://git.kernel.org/stable/c/04a2c4b4511d186b0fce685da21085a5d4acd370
    Patch
  • git.kernel.org https://git.kernel.org/stable/c/237e416eb62101f21b28c9e6e564d10efe1ecc6f
    Patch
  • git.kernel.org https://git.kernel.org/stable/c/628fc28f42d979f36dbf75a6129ac7730e30c04e
    Patch
  • git.kernel.org https://git.kernel.org/stable/c/749528086620f8012b83ae032a80f6ffa80c45cd
    Patch
  • git.kernel.org https://git.kernel.org/stable/c/9f61fa6a2a89a610120bc4e5d24379c667314b5c
    Patch
  • git.kernel.org https://git.kernel.org/stable/c/b4159c5a90c03f8acd3de345a7f5fc63b0909818
    Patch
  • git.kernel.org https://git.kernel.org/stable/c/d4f9351243c17865a8cdbe6b3ccd09d0b13a7bcc
    Patch
  • git.kernel.org https://git.kernel.org/stable/c/dfd1f4ea98c3bd3a03d12169b5b2daa1f0a3e4ae
    Patch
  • git.kernel.org https://git.kernel.org/stable/c/f95638a8f22eba307dceddf5aef9ae2326bbcf98
    Patch
  • lists.debian.org https://lists.debian.org/debian-lts-announce/2025/10/msg00007.html
    Mailing ListThird Party Advisory
  • lists.debian.org https://lists.debian.org/debian-lts-announce/2025/10/msg00008.html
    Mailing ListThird Party Advisory

Remediation

  • git.kernel.org https://git.kernel.org/stable/c/04a2c4b4511d186b0fce685da21085a5d4acd370
    Patch
  • git.kernel.org https://git.kernel.org/stable/c/237e416eb62101f21b28c9e6e564d10efe1ecc6f
    Patch
  • git.kernel.org https://git.kernel.org/stable/c/628fc28f42d979f36dbf75a6129ac7730e30c04e
    Patch
  • git.kernel.org https://git.kernel.org/stable/c/749528086620f8012b83ae032a80f6ffa80c45cd
    Patch
  • git.kernel.org https://git.kernel.org/stable/c/9f61fa6a2a89a610120bc4e5d24379c667314b5c
    Patch
  • git.kernel.org https://git.kernel.org/stable/c/b4159c5a90c03f8acd3de345a7f5fc63b0909818
    Patch
  • git.kernel.org https://git.kernel.org/stable/c/d4f9351243c17865a8cdbe6b3ccd09d0b13a7bcc
    Patch
  • git.kernel.org https://git.kernel.org/stable/c/dfd1f4ea98c3bd3a03d12169b5b2daa1f0a3e4ae
    Patch
  • git.kernel.org https://git.kernel.org/stable/c/f95638a8f22eba307dceddf5aef9ae2326bbcf98
    Patch