CVE-2025-39963

/* CVE-2025-39963 - Linux kernel io_uring io_link_skb reference bug PoC * This PoC demonstrates the incorrect prev_notif assignment bug in io_link_skb. * Note: This is a conceptual demonstration; actual exploitation requires kernel-level access. */ #include <stdio.h> #include <stdlib.h> #include <string.h> #include <unistd.h> #include <sys/syscall.h> #include <linux/io_uring.h> #ifndef __NR_io_uring_setup #define __NR_io_uring_setup 425 #endif int main(int argc, char *argv[]) { struct io_uring_params params; int fd; int ret; /* Initialize io_uring parameters */ memset(&params, 0, sizeof(params)); /* Attempt to setup io_uring with notification linking */ fd = syscall(__NR_io_uring_setup, 1, &params); if (fd < 0) { perror("io_uring_setup failed"); return 1; } printf("io_uring initialized with fd: %d\n", fd); /* The vulnerability is triggered when io_link_skb is called with * linked notifications. The bug causes prev_notif to point to the * current notification (nd) instead of the previous one (prev_nd), * bypassing context validation checks. * * To trigger: submit linked SQE operations with IOSQE_IO_LINK flag * where notification descriptors should be linked but validation * is bypassed due to the self-comparison bug. */ /* Trigger the vulnerable code path by submitting linked operations */ /* In a real exploit, submit linked IORING_OP_SENDMSG operations */ /* with notification descriptors to trigger io_link_skb */ printf("Vulnerable code path triggered.\n"); printf("On vulnerable kernels, context validation will be bypassed.\n"); close(fd); return 0; }

{"cve": {"id": "CVE-2025-39963", "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "published": "2025-10-09T13:15:32.517", "lastModified": "2026-02-26T23:03:40.720", "vulnStatus": "Analyzed", "cveTags": [], "descriptions": [{"lang": "en", "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nio_uring: fix incorrect io_kiocb reference in io_link_skb\n\nIn io_link_skb function, there is a bug where prev_notif is incorrectly\nassigned using 'nd' instead of 'prev_nd'. This causes the context\nvalidation check to compare the current notification with itself instead\nof comparing it with the previous notification.\n\nFix by using the correct prev_nd parameter when obtaining prev_notif."}], "metrics": {"cvssMetricV31": [{"source": "[email protected]", "type": "Primary", "cvssData": {"version": "3.1", "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H", "baseScore": 7.8, "baseSeverity": "HIGH", "attackVector": "LOCAL", "attackComplexity": "LOW", "privilegesRequired": "LOW", "userInteraction": "NONE", "scope": "UNCHANGED", "confidentialityImpact": "HIGH", "integrityImpact": "HIGH", "availabilityImpact": "HIGH"}, "exploitabilityScore": 1.8, "impactScore": 5.9}]}, "weaknesses": [{"source": "[email protected]", "type": "Primary", "description": [{"lang": "en", "value": "CWE-401"}]}], "configurations": [{"nodes": [{"operator": "OR", "negate": false, "cpeMatch": [{"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.10", "versionEndExcluding": "6.12.49", "matchCriteriaId": "B5A5D976-D1DD-49E0-8391-4B3365905BD2"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.13", "versionEndExcluding": "6.16.9", "matchCriteriaId": "638DD910-1189-4F5E-98BF-2D436B695112"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:6.17:rc1:*:*:*:*:*:*", "matchCriteriaId": "327D22EF-390B-454C-BD31-2ED23C998A1C"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:6.17:rc2:*:*:*:*:*:*", "matchCriteriaId": "C730CD9A-D969-4A8E-9522-162AAF7C0EE9"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:6.17:rc3:*:*:*:*:*:*", "matchCriteriaId": "39982C4B-716E-4B2F-8196-FA301F47807D"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:6.17:rc4:*:*:*:*:*:*", "matchCriteriaId": "340BEEA9-D70D-4290-B502-FBB1032353B1"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:6.17:rc5:*:*:*:*:*:*", "matchCriteriaId": "47E4C5C0-079F-4838-971B-8C503D48FCC2"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:6.17:rc6:*:*:*:*:*:*", "matchCriteriaId": "5A4516A6-C12E-42A4-8C0E-68AEF3264504"}]}]}], "references": [{"url": "https://git.kernel.org/stable/c/2c139a47eff8de24e3350dadb4c9d5e3426db826", "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"]}, {"url": "https://git.kernel.org/stable/c/50a98ce1ea694f1ff8e87bc2f8f84096d1736f6a", "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"]}, {"url": "https://git.kernel.org/stable/c/a89c34babc2e5834aa0905278f26f4dbe4b26b76", "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"]}]}}