{ "dataType": "CVE_RECORD", "dataVersion": "5.2", "cveMetadata": { "cveId": "CVE-2021-47656", "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "state": "PUBLISHED", "assignerShortName": "Linux", "dateReserved": "2025-02-26T01:48:21.521Z", "datePublished": "2025-02-26T01:54:20.069Z", "dateUpdated": "2026-08-05T08:48:47.063Z" }, "containers": { "cna": { "providerMetadata": { "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "shortName": "Linux", "dateUpdated": "2026-08-05T08:48:47.063Z" }, "descriptions": [ { "lang": "en", "value": "In the Linux kernel, the following vulnerability has been resolved:\n\njffs2: fix use-after-free in jffs2_clear_xattr_subsystem\n\nWhen we mount a jffs2 image, assume that the first few blocks of\nthe image are normal and contain at least one xattr-related inode,\nbut the next block is abnormal. As a result, an error is returned\nin jffs2_scan_eraseblock(). jffs2_clear_xattr_subsystem() is then\ncalled in jffs2_build_filesystem() and then again in\njffs2_do_fill_super().\n\nFinally we can observe the following report:\n ==================================================================\n BUG: KASAN: use-after-free in jffs2_clear_xattr_subsystem+0x95/0x6ac\n Read of size 8 at addr ffff8881243384e0 by task mount/719\n\n Call Trace:\n dump_stack+0x115/0x16b\n jffs2_clear_xattr_subsystem+0x95/0x6ac\n jffs2_do_fill_super+0x84f/0xc30\n jffs2_fill_super+0x2ea/0x4c0\n mtd_get_sb+0x254/0x400\n mtd_get_sb_by_nr+0x4f/0xd0\n get_tree_mtd+0x498/0x840\n jffs2_get_tree+0x25/0x30\n vfs_get_tree+0x8d/0x2e0\n path_mount+0x50f/0x1e50\n do_mount+0x107/0x130\n __se_sys_mount+0x1c5/0x2f0\n __x64_sys_mount+0xc7/0x160\n do_syscall_64+0x45/0x70\n entry_SYSCALL_64_after_hwframe+0x44/0xa9\n\n Allocated by task 719:\n kasan_save_stack+0x23/0x60\n __kasan_kmalloc.constprop.0+0x10b/0x120\n kasan_slab_alloc+0x12/0x20\n kmem_cache_alloc+0x1c0/0x870\n jffs2_alloc_xattr_ref+0x2f/0xa0\n jffs2_scan_medium.cold+0x3713/0x4794\n jffs2_do_mount_fs.cold+0xa7/0x2253\n jffs2_do_fill_super+0x383/0xc30\n jffs2_fill_super+0x2ea/0x4c0\n [...]\n\n Freed by task 719:\n kmem_cache_free+0xcc/0x7b0\n jffs2_free_xattr_ref+0x78/0x98\n jffs2_clear_xattr_subsystem+0xa1/0x6ac\n jffs2_do_mount_fs.cold+0x5e6/0x2253\n jffs2_do_fill_super+0x383/0xc30\n jffs2_fill_super+0x2ea/0x4c0\n [...]\n\n The buggy address belongs to the object at ffff8881243384b8\n which belongs to the cache jffs2_xattr_ref of size 48\n The buggy address is located 40 bytes inside of\n 48-byte region [ffff8881243384b8, ffff8881243384e8)\n [...]\n ==================================================================\n\nThe triggering of the BUG is shown in the following stack:\n-----------------------------------------------------------\njffs2_fill_super\n jffs2_do_fill_super\n jffs2_do_mount_fs\n jffs2_build_filesystem\n jffs2_scan_medium\n jffs2_scan_eraseblock <--- ERROR\n jffs2_clear_xattr_subsystem <--- free\n jffs2_clear_xattr_subsystem <--- free again\n-----------------------------------------------------------\n\nAn error is returned in jffs2_do_mount_fs(). If the error is returned\nby jffs2_sum_init(), the jffs2_clear_xattr_subsystem() does not need to\nbe executed. If the error is returned by jffs2_build_filesystem(), the\njffs2_clear_xattr_subsystem() also does not need to be executed again.\nSo move jffs2_clear_xattr_subsystem() from 'out_inohash' to 'out_root'\nto fix this UAF problem." } ], "metrics": [ { "cvssV3_1": { "version": "3.1", "vectorString": "CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H", "baseScore": 7.8, "baseSeverity": "HIGH" }, "scenarios": [ { "lang": "en", "value": "AV:L - The bug is reached only through the local mount path (mount → jffs2_get_tree → get_tree_mtd → jffs2_fill_super → jffs2_do_fill_super → jffs2_do_mount_fs → jffs2_build_filesystem), parsing an MTD/JFFS2 image; there is no network-facing consumer.\nAC:L - An attacker who crafts the image fully controls the trigger—place valid XREF/XATTR nodes in early eraseblocks so jffs2_alloc_xattr_ref() populates xref_temp, then make a later block fail jffs2_scan_eraseblock()—with no race or attacker-uncontrollable condition.\nPR:N - The attacker needs no account on the target; they only supply the crafted JFFS2/MTD image (firmware blob, flash/SD contents), and CAP_SYS_ADMIN belongs to the victim or tooling that mounts it, matching the crafted-filesystem-image pattern.\nUI:R - Exploitation requires a victim (root, firmware updater, or automounter) to mount the attacker-supplied JFFS2 image so the failing scan hits the double clear_xattr path.\nS:U - The use-after-free corrupts kernel slab memory within the same host OS security authority; no VM escape, IOMMU bypass, or other cross-boundary compromise occurs.\nC:H - jffs2_clear_xattr_subsystem() frees xref_temp without NULLing it, so the second call reads ref->next from freed jffs2_xattr_ref slab objects; per guidance a UAF enables arbitrary kernel memory disclosure.\nI:H - The second pass double-frees attacker-populated jffs2_xattr_ref objects, enabling classic heap spraying and overlapping allocations for arbitrary write / control-flow hijack.\nA:H - The KASAN-confirmed use-after-free during mount produces a kernel oops/panic even without full exploitation, and is repeatable on every mount of the crafted image." } ] } ], "affected": [ { "product": "Linux", "vendor": "Linux", "defaultStatus": "unaffected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": [ "fs/jffs2/fs.c" ], "versions": [ { "version": "aa98d7cf59b5b0764d3502662053489585faf2fe", "lessThan": "9150cb625b46f68d524f4cfd491f1aafc23e10a9", "status": "affected", "versionType": "git" }, { "version": "aa98d7cf59b5b0764d3502662053489585faf2fe", "lessThan": "3bd2454162ec6bbb5503233c804fce6e4b6dcec5", "status": "affected", "versionType": "git" }, { "version": "aa98d7cf59b5b0764d3502662053489585faf2fe", "lessThan": "c3b07c875fa8f906f932976460fd14798596f101", "status": "affected", "versionType": "git" }, { "version": "aa98d7cf59b5b0764d3502662053489585faf2fe", "lessThan": "30bf7244acf32f19cb722c39f7bc1c2a9f300422", "status": "affected", "versionType": "git" }, { "version": "aa98d7cf59b5b0764d3502662053489585faf2fe", "lessThan": "7bb7428dd73991bf4b3a7a61b493ca50046c2b13", "status": "affected", "versionType": "git" }, { "version": "aa98d7cf59b5b0764d3502662053489585faf2fe", "lessThan": "7a75740206af5f17e9f3efa384211cba70213da1", "status": "affected", "versionType": "git" }, { "version": "aa98d7cf59b5b0764d3502662053489585faf2fe", "lessThan": "22327bd7988f21de3a53c1373f3b81542bfe1f44", "status": "affected", "versionType": "git" }, { "version": "aa98d7cf59b5b0764d3502662053489585faf2fe", "lessThan": "8c0f024f29e055840a5a89fe23b96ae3f921afed", "status": "affected", "versionType": "git" }, { "version": "aa98d7cf59b5b0764d3502662053489585faf2fe", "lessThan": "4c7c44ee1650677fbe89d86edbad9497b7679b5c", "status": "affected", "versionType": "git" } ] }, { "product": "Linux", "vendor": "Linux", "defaultStatus": "affected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": [ "fs/jffs2/fs.c" ], "versions": [ { "version": "2.6.18", "status": "affected" }, { "version": "0", "lessThan": "2.6.18", "status": "unaffected", "versionType": "semver" }, { "version": "4.9.311", "lessThanOrEqual": "4.9.*", "status": "unaffected", "versionType": "semver" }, { "version": "4.14.276", "lessThanOrEqual": "4.14.*", "status": "unaffected", "versionType": "semver" }, { "version": "4.19.238", "lessThanOrEqual": "4.19.*", "status": "unaffected", "versionType": "semver" }, { "version": "5.4.189", "lessThanOrEqual": "5.4.*", "status": "unaffected", "versionType": "semver" }, { "version": "5.10.110", "lessThanOrEqual": "5.10.*", "status": "unaffected", "versionType": "semver" }, { "version": "5.15.33", "lessThanOrEqual": "5.15.*", "status": "unaffected", "versionType": "semver" }, { "version": "5.16.19", "lessThanOrEqual": "5.16.*", "status": "unaffected", "versionType": "semver" }, { "version": "5.17.2", "lessThanOrEqual": "5.17.*", "status": "unaffected", "versionType": "semver" }, { "version": "5.18", "lessThanOrEqual": "*", "status": "unaffected", "versionType": "original_commit_for_fix" } ] } ], "cpeApplicability": [ { "nodes": [ { "operator": "OR", "negate": false, "cpeMatch": [ { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "2.6.18", "versionEndExcluding": "4.9.311" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "2.6.18", "versionEndExcluding": "4.14.276" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "2.6.18", "versionEndExcluding": "4.19.238" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "2.6.18", "versionEndExcluding": "5.4.189" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "2.6.18", "versionEndExcluding": "5.10.110" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "2.6.18", "versionEndExcluding": "5.15.33" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "2.6.18", "versionEndExcluding": "5.16.19" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "2.6.18", "versionEndExcluding": "5.17.2" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "2.6.18", "versionEndExcluding": "5.18" } ] } ] } ], "references": [ { "url": "https://git.kernel.org/stable/c/9150cb625b46f68d524f4cfd491f1aafc23e10a9" }, { "url": "https://git.kernel.org/stable/c/3bd2454162ec6bbb5503233c804fce6e4b6dcec5" }, { "url": "https://git.kernel.org/stable/c/c3b07c875fa8f906f932976460fd14798596f101" }, { "url": "https://git.kernel.org/stable/c/30bf7244acf32f19cb722c39f7bc1c2a9f300422" }, { "url": "https://git.kernel.org/stable/c/7bb7428dd73991bf4b3a7a61b493ca50046c2b13" }, { "url": "https://git.kernel.org/stable/c/7a75740206af5f17e9f3efa384211cba70213da1" }, { "url": "https://git.kernel.org/stable/c/22327bd7988f21de3a53c1373f3b81542bfe1f44" }, { "url": "https://git.kernel.org/stable/c/8c0f024f29e055840a5a89fe23b96ae3f921afed" }, { "url": "https://git.kernel.org/stable/c/4c7c44ee1650677fbe89d86edbad9497b7679b5c" } ], "title": "jffs2: fix use-after-free in jffs2_clear_xattr_subsystem", "x_generator": { "engine": "bippy-1.2.0" } }, "adp": [ { "metrics": [ { "cvssV3_1": { "scope": "UNCHANGED", "version": "3.1", "baseScore": 7.8, "attackVector": "LOCAL", "baseSeverity": "HIGH", "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H", "integrityImpact": "HIGH", "userInteraction": "NONE", "attackComplexity": "LOW", "availabilityImpact": "HIGH", "privilegesRequired": "LOW", "confidentialityImpact": "HIGH" } }, { "other": { "type": "ssvc", "content": { "id": "CVE-2021-47656", "role": "CISA Coordinator", "options": [ { "Exploitation": "none" }, { "Automatable": "no" }, { "Technical Impact": "total" } ], "version": "2.0.3", "timestamp": "2025-02-27T17:59:35.381270Z" } } } ], "problemTypes": [ { "descriptions": [ { "lang": "en", "type": "CWE", "cweId": "CWE-416", "description": "CWE-416 Use After Free" } ] } ], "title": "CISA ADP Vulnrichment", "providerMetadata": { "orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0", "shortName": "CISA-ADP", "dateUpdated": "2025-02-27T18:02:30.510Z" } } ] } }