{ "schemaVersion": 1, "attribution": [ { "source": "CISA Known Exploited Vulnerabilities", "url": "https://www.cisa.gov/known-exploited-vulnerabilities-catalog", "licence": "US government work" }, { "source": "GitHub Advisory Database", "url": "https://github.com/advisories", "licence": "CC BY 4.0" }, { "source": "Have I Been Pwned", "url": "https://haveibeenpwned.com/", "licence": "CC BY 4.0" }, { "source": "CVE Program (CVE records)", "url": "https://www.cve.org/Legal/TermsOfUse", "licence": "CVE Terms of Use", "notice": "Copyright © 1999-2026, The MITRE Corporation. CVE is a trademark and the CVE logo is a registered trademark of The MITRE Corporation.", "terms": "CVE Usage: MITRE hereby grants you a perpetual, worldwide, non-exclusive, no-charge, royalty-free, irrevocable copyright license to reproduce, prepare derivative works of, publicly display, publicly perform, sublicense, and distribute Common Vulnerabilities and Exposures (CVE™). Any copy you make for such purposes is authorized provided that you reproduce MITRE's copyright designation and this license in any such copy." }, { "source": "FIRST EPSS", "url": "https://www.first.org/epss/", "licence": "free to use; FIRST requests attribution" } ], "record": { "id": "CVE-2025-39756", "sourceURL": "https://www.cve.org/CVERecord?id=CVE-2025-39756", "idYear": 2025, "status": "PUBLISHED", "publishedAt": "2025-09-11T16:52:26.136Z", "updatedAt": "2026-10-15T01:08:10.812Z", "importedAt": "2026-10-24T01:57:34.152Z", "snapshot": { "id": "cve_2026-10-24_midnight_baseline", "at": "2026-10-24T00:00:00.000Z", "source": "https://github.com/CVEProject/cvelistV5/releases/tag/cve_2026-10-24_0100Z" }, "facts": { "title": "fs: Prevent file descriptor table allocations exceeding INT_MAX", "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 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.", "affected": [ { "vendor": "Linux", "product": "Linux", "defaultStatus": "unaffected", "versions": [ { "version": "9cfe015aa424b3c003baba3841a60dd9b5ad319b", "status": "affected", "versionType": "git", "lessThan": "b4159c5a90c03f8acd3de345a7f5fc63b0909818" }, { "version": "9cfe015aa424b3c003baba3841a60dd9b5ad319b", "status": "affected", "versionType": "git", "lessThan": "f95638a8f22eba307dceddf5aef9ae2326bbcf98" }, { "version": "9cfe015aa424b3c003baba3841a60dd9b5ad319b", "status": "affected", "versionType": "git", "lessThan": "749528086620f8012b83ae032a80f6ffa80c45cd" }, { "version": "9cfe015aa424b3c003baba3841a60dd9b5ad319b", "status": "affected", "versionType": "git", "lessThan": "628fc28f42d979f36dbf75a6129ac7730e30c04e" }, { "version": "9cfe015aa424b3c003baba3841a60dd9b5ad319b", "status": "affected", "versionType": "git", "lessThan": "237e416eb62101f21b28c9e6e564d10efe1ecc6f" }, { "version": "9cfe015aa424b3c003baba3841a60dd9b5ad319b", "status": "affected", "versionType": "git", "lessThan": "d4f9351243c17865a8cdbe6b3ccd09d0b13a7bcc" }, { "version": "9cfe015aa424b3c003baba3841a60dd9b5ad319b", "status": "affected", "versionType": "git", "lessThan": "9f61fa6a2a89a610120bc4e5d24379c667314b5c" }, { "version": "9cfe015aa424b3c003baba3841a60dd9b5ad319b", "status": "affected", "versionType": "git", "lessThan": "dfd1f4ea98c3bd3a03d12169b5b2daa1f0a3e4ae" }, { "version": "9cfe015aa424b3c003baba3841a60dd9b5ad319b", "status": "affected", "versionType": "git", "lessThan": "04a2c4b4511d186b0fce685da21085a5d4acd370" } ] }, { "vendor": "Linux", "product": "Linux", "defaultStatus": "affected", "versions": [ { "version": "2.6.25", "status": "affected" }, { "version": "0", "status": "unaffected", "versionType": "semver", "lessThan": "2.6.25" }, { "version": "5.4.297", "status": "unaffected", "versionType": "semver", "lessThanOrEqual": "5.4.*" }, { "version": "5.10.241", "status": "unaffected", "versionType": "semver", "lessThanOrEqual": "5.10.*" }, { "version": "5.15.190", "status": "unaffected", "versionType": "semver", "lessThanOrEqual": "5.15.*" }, { "version": "6.1.149", "status": "unaffected", "versionType": "semver", "lessThanOrEqual": "6.1.*" }, { "version": "6.6.103", "status": "unaffected", "versionType": "semver", "lessThanOrEqual": "6.6.*" }, { "version": "6.12.43", "status": "unaffected", "versionType": "semver", "lessThanOrEqual": "6.12.*" }, { "version": "6.15.11", "status": "unaffected", "versionType": "semver", "lessThanOrEqual": "6.15.*" }, { "version": "6.16.2", "status": "unaffected", "versionType": "semver", "lessThanOrEqual": "6.16.*" }, { "version": "6.17", "status": "unaffected", "versionType": "original_commit_for_fix", "lessThanOrEqual": "*" } ] } ] } } }