{"id":"CVE-2025-39756","title":"In the Linux kernel, the following vulnerability has been resolved:\n\nfs: Prevent file descriptor table allocations exceeding INT_MAX\n\nWhen sysctl_nr_open is set to a very high value (for example, 1073741816\nas set by systemd), processes …","summary":"In the Linux kernel, the following vulnerability has been resolved:\n\nfs: Prevent file descriptor table allocations exceeding INT_MAX\n\nWhen sysctl_nr_open is set to a very high value (for example, 1073741816\nas set by systemd), processes …","severity":"medium","cvss":5.5,"cvssVector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H","cwe":["CWE-401"],"vendor":"linux","product":"linux_kernel","affected":["linux_kernel >= 2.6.25, < 5.4.297","linux_kernel >= 5.5, < 5.10.241","linux_kernel >= 5.11, < 5.15.190","linux_kernel >= 5.16, < 6.1.149","linux_kernel >= 6.2, < 6.6.103","linux_kernel >= 6.7, < 6.12.43","linux_kernel >= 6.13, < 6.15.11","linux_kernel >= 6.16, < 6.16.2","debian_linux = 11.0"],"patched":["linux_kernel 6.16.2"],"published":"2025-09-11","updated":"2026-10-15","sourceUpdated":"2026-10-15T02:17:59.890","source":"NVD","sourceUrl":"https://nvd.nist.gov/vuln/detail/CVE-2025-39756","references":[{"url":"https://git.kernel.org/stable/c/04a2c4b4511d186b0fce685da21085a5d4acd370","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/237e416eb62101f21b28c9e6e564d10efe1ecc6f","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/628fc28f42d979f36dbf75a6129ac7730e30c04e","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/749528086620f8012b83ae032a80f6ffa80c45cd","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/9f61fa6a2a89a610120bc4e5d24379c667314b5c","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/b4159c5a90c03f8acd3de345a7f5fc63b0909818","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/d4f9351243c17865a8cdbe6b3ccd09d0b13a7bcc","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/dfd1f4ea98c3bd3a03d12169b5b2daa1f0a3e4ae","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/f95638a8f22eba307dceddf5aef9ae2326bbcf98","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://lists.debian.org/debian-lts-announce/2025/10/msg00007.html","label":"af854a3a-2127-422b-91ae-364da2661108"},{"url":"https://lists.debian.org/debian-lts-announce/2025/10/msg00008.html","label":"af854a3a-2127-422b-91ae-364da2661108"},{"url":"https://cert-portal.siemens.com/productcert/html/ssa-019113.html","label":"0b142b55-0307-4c5a-b3c9-f314f3fb7c5e"},{"url":"https://cert-portal.siemens.com/productcert/html/ssa-032379.html","label":"0b142b55-0307-4c5a-b3c9-f314f3fb7c5e"},{"url":"https://cert-portal.siemens.com/productcert/html/ssa-082556.html","label":"0b142b55-0307-4c5a-b3c9-f314f3fb7c5e"},{"url":"https://cert-portal.siemens.com/productcert/html/ssa-457936.html","label":"0b142b55-0307-4c5a-b3c9-f314f3fb7c5e"}],"tags":["nvd","cve.org"],"epss":0.00183,"epssPercentile":0.07778,"ingestedAt":"2026-09-08T15:33:26.997Z","slug":"CVE-2025-39756","body":"## Overview\n\nIn the Linux kernel, the following vulnerability has been resolved:\n\nfs: Prevent file descriptor table allocations exceeding INT_MAX\n\nWhen sysctl_nr_open is set to a very high value (for example, 1073741816\nas set by systemd), processes attempting to use file descriptors near\nthe limit can trigger massive memory allocation attempts that exceed\nINT_MAX, resulting in a WARNING in mm/slub.c:\n\n WARNING: CPU: 0 PID: 44 at mm/slub.c:5027 __kvmalloc_node_noprof+0x21a/0x288\n\nThis happens because kvmalloc_array() and kvmalloc() check if the\nrequested size exceeds INT_MAX and emit a warning when the allocation is\nnot flagged with __GFP_NOWARN.\n\nSpecifically, when nr_open is set to 1073741816 (0x3ffffff8) and a\nprocess calls dup2(oldfd, 1073741880), the kernel attempts to allocate:\n- File descriptor array: 1073741880 * 8 bytes = 8,589,935,040 bytes\n- Multiple bitmaps: ~400MB\n- Total allocation size: > 8GB (exceeding INT_MAX = 2,147,483,647)\n\nReproducer:\n1. Set /proc/sys/fs/nr_open to 1073741816:\n # echo 1073741816 > /proc/sys/fs/nr_open\n\n2. Run a program that uses a high file descriptor:\n #include \n #include \n\n int main() {\n struct rlimit rlim = {1073741824, 1073741824};\n setrlimit(RLIMIT_NOFILE, &rlim);\n dup2(2, 1073741880); // Triggers the warning\n return 0;\n }\n\n3. Observe WARNING in dmesg at mm/slub.c:5027\n\nsystemd commit a8b627a introduced automatic bumping of fs.nr_open to the\nmaximum possible value. The rationale was that systems with memory\ncontrol groups (memcg) no longer need separate file descriptor limits\nsince memory is properly accounted. However, this change overlooked\nthat:\n\n1. The kernel's allocation functions still enforce INT_MAX as a maximum\n size regardless of memcg accounting\n2. Programs and tests that legitimately test file descriptor limits can\n inadvertently trigger massive allocations\n3. The resulting allocations (>8GB) are impractical and will always fail\n\nsystemd's algorithm starts with INT_MAX and keeps halving the value\nuntil the kernel accepts it. On most systems, this results in nr_open\nbeing set to 1073741816 (0x3ffffff8), which is just under 1GB of file\ndescriptors.\n\nWhile processes rarely use file descriptors near this limit in normal\noperation, certain selftests (like\ntools/testing/selftests/core/unshare_test.c) and programs that test file\ndescriptor limits can trigger this issue.\n\nFix this by adding a check in alloc_fdtable() to ensure the requested\nallocation size does not exceed INT_MAX. This causes the operation to\nfail with -EMFILE instead of triggering a kernel warning and avoids the\nimpractical >8GB memory allocation request.\n\n## Affected\n\n- `linux_kernel >= 2.6.25, < 5.4.297`\n- `linux_kernel >= 5.5, < 5.10.241`\n- `linux_kernel >= 5.11, < 5.15.190`\n- `linux_kernel >= 5.16, < 6.1.149`\n- `linux_kernel >= 6.2, < 6.6.103`\n- `linux_kernel >= 6.7, < 6.12.43`\n- `linux_kernel >= 6.13, < 6.15.11`\n- `linux_kernel >= 6.16, < 6.16.2`\n- `debian_linux = 11.0`\n\n## Remediation\n\nUpgrade past the affected range:\n\n- `linux_kernel 6.16.2`","depth":"sunlit","depthScore":30,"depthScoreParts":{"impact":30.3,"likelihood":0,"exploitation":0,"ransomware":0},"changes":[{"seq":221545,"id":"CVE-2025-39756","ts":1792035257573,"field":"cvss","old":null,"new":"5.5"},{"seq":221544,"id":"CVE-2025-39756","ts":1792035257573,"field":"severity","old":"none","new":"medium"}]}