CVE-2026-43288

#!/bin/bash # PoC for CVE-2026-43288 # Target: Linux Kernel with ext4 DOUBLE_CHECK macro enabled # This script reproduces the kernel panic by creating a specific # filesystem configuration and mounting it. # 1. Setup environment: Ensure /dev/sda is a writable block device # 2. Create ext4 filesystem with 1k block size mkfs.ext4 -F -q -b 1024 /dev/sda 5G # 3. Enable quota and project features tune2fs -O quota,project /dev/sda # 4. Mount the filesystem # This triggers the ext4_mb_init path before percpu counters are ready. # If DOUBLE_CHECK is enabled and bitmap validation fails, kernel panics. mount /dev/sda /tmp/test

{"cve": {"id": "CVE-2026-43288", "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "published": "2026-05-08T14:16:35.737", "lastModified": "2026-05-15T16:45:42.857", "vulnStatus": "Analyzed", "cveTags": [], "descriptions": [{"lang": "en", "value": "In the Linux kernel, the following vulnerability has been resolved:\n\next4: move ext4_percpu_param_init() before ext4_mb_init()\n\nWhen running `kvm-xfstests -c ext4/1k -C 1 generic/383` with the\n`DOUBLE_CHECK` macro defined, the following panic is triggered:\n\n==================================================================\nEXT4-fs error (device vdc): ext4_validate_block_bitmap:423:\n comm mount: bg 0: bad block bitmap checksum\nBUG: unable to handle page fault for address: ff110000fa2cc000\nPGD 3e01067 P4D 3e02067 PUD 0\nOops: Oops: 0000 [#1] SMP NOPTI\nCPU: 0 UID: 0 PID: 2386 Comm: mount Tainted: G W\n 6.18.0-gba65a4e7120a-dirty #1152 PREEMPT(none)\nRIP: 0010:percpu_counter_add_batch+0x13/0xa0\nCall Trace:\n <TASK>\n ext4_mark_group_bitmap_corrupted+0xcb/0xe0\n ext4_validate_block_bitmap+0x2a1/0x2f0\n ext4_read_block_bitmap+0x33/0x50\n mb_group_bb_bitmap_alloc+0x33/0x80\n ext4_mb_add_groupinfo+0x190/0x250\n ext4_mb_init_backend+0x87/0x290\n ext4_mb_init+0x456/0x640\n __ext4_fill_super+0x1072/0x1680\n ext4_fill_super+0xd3/0x280\n get_tree_bdev_flags+0x132/0x1d0\n vfs_get_tree+0x29/0xd0\n vfs_cmd_create+0x59/0xe0\n __do_sys_fsconfig+0x4f6/0x6b0\n do_syscall_64+0x50/0x1f0\n entry_SYSCALL_64_after_hwframe+0x76/0x7e\n==================================================================\n\nThis issue can be reproduced using the following commands:\n mkfs.ext4 -F -q -b 1024 /dev/sda 5G\n tune2fs -O quota,project /dev/sda\n mount /dev/sda /tmp/test\n\nWith DOUBLE_CHECK defined, mb_group_bb_bitmap_alloc() reads\nand validates the block bitmap. When the validation fails,\next4_mark_group_bitmap_corrupted() attempts to update\nsbi->s_freeclusters_counter. However, this percpu_counter has not been\ninitialized yet at this point, which leads to the panic described above.\n\nFix this by moving the execution of ext4_percpu_param_init() to occur\nbefore ext4_mb_init(), ensuring the per-CPU counters are initialized\nbefore they are used."}], "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:N/I:N/A:H", "baseScore": 5.5, "baseSeverity": "MEDIUM", "attackVector": "LOCAL", "attackComplexity": "LOW", "privilegesRequired": "LOW", "userInteraction": "NONE", "scope": "UNCHANGED", "confidentialityImpact": "NONE", "integrityImpact": "NONE", "availabilityImpact": "HIGH"}, "exploitabilityScore": 1.8, "impactScore": 3.6}]}, "weaknesses": [{"source": "[email protected]", "type": "Primary", "description": [{"lang": "en", "value": "CWE-908"}]}], "configurations": [{"nodes": [{"operator": "OR", "negate": false, "cpeMatch": [{"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "3.17", "versionEndExcluding": "6.6.128", "matchCriteriaId": "A1706372-54DA-4071-B3F0-1DF561FE84E8"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.7", "versionEndExcluding": "6.12.75", "matchCriteriaId": "BCE16369-98ED-41CF-8995-DFDC10B288D2"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.13", "versionEndExcluding": "6.18.16", "matchCriteriaId": "B4B8CDA9-BADF-4CF5-8B3B-702DE8EEA40B"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.19", "versionEndExcluding": "6.19.6", "matchCriteriaId": "373EEEDA-FAA1-4FB4-B6ED-DB4DD99DBE67"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:7.0:rc1:*:*:*:*:*:*", "matchCriteriaId": "F253B622-8837-4245-BCE5-A7BF8FC76A16"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:7.0:rc2:*:*:*:*:*:*", "matchCriteriaId": "4AE85AD8-4641-4E7C-A2F4-305E2CD9EE64"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:7.0:rc3:*:*:*:*:*:*", "matchCriteriaId": "F666C8D8-6538-46D4-B318-87610DE64C34"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:7.0:rc4:*:*:*:*:*:*", "matchCriteriaId": "02259FDA-961B-47BC-AE7F-93D7EC6E90C2"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:7.0:rc5:*:*:*:*:*:*", "matchCriteriaId": "58A9FEFF-C040-420D-8F0A-BFDAAA1DF258"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:7.0:rc6:*:*:*:*:*:*", "matchCriteriaId": "1D2315C0-D46F-4F85-9754-F9E5E11374A6"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:7.0:rc7:*:*:*:*:*:*", "matchCriteriaId": "512EE3A8-A590-4501-9A94-5D4B268D6138"}]}]}], "references": [{"url": "https://git.kernel.org/stable/c/0d5fcb063cdabb9aeaa8554b7fedad2092c4150e", "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"]}, {"url": ... (truncated)