{"answers":{"affected":"It affects 1 product.","exploited":"There is no known exploitation of CVE-2021-47656 in the wild and no public exploit code.","fix":"Apply the vendor's patch.","what":"CVE-2021-47656 is a high-severity use after free vulnerability in Linux kernel, published on 26 Feb 2025. It can only be exploited from the same machine or local network, and only if a user opens a file or follows a link."},"fix_prompt":"Check this codebase for CVE-2021-47656 and fix it if it is affected.\n\nWhat it is: CVE-2021-47656 is a high-severity use after free vulnerability in Linux kernel, published on 26 Feb 2025. It can only be exploited from the same machine or local network, and only if a user opens a file or follows a link.\nExploitation: There is no known exploitation of CVE-2021-47656 in the wild and no public exploit code.\n\nAffected product: Linux kernel. No package-level version data is available, so check the vendor advisory linked from the reference page.\n\nTask:\n1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.\n2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.\n3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.\n4. Run the tests and summarise what changed and why.\n5. If nothing in the project is affected, say so and change nothing.\n\nReference: https://insights.sbomify.com/CVE-2021-47656/ (Markdown: https://insights.sbomify.com/CVE-2021-47656/index.md)","id":"CVE-2021-47656","markdown":"https://insights.sbomify.com/CVE-2021-47656/index.md","name":"CVE-2021-47656","record":{"aliases":["DEBIAN-CVE-2021-47656","GHSA-4mx7-h455-mwxv","UBUNTU-CVE-2021-47656"],"analysis":{"component_type":"kernel","fix_type":"patch","impacts":["denial_of_service","code_execution"],"network_reachable":"adjacent_or_local","non_default_config":false,"product_category":"Linux kernel","requires_auth":"none","summary":"A use-after-free vulnerability in the Linux kernel's JFFS2 filesystem allows attackers to cause a denial of service or potentially execute code via a crafted image.","user_interaction":"required","vuln_class":"use_after_free"},"analysis_generated_by":"qwen3.8-flash-next","assigner":"Linux","cpe":[{"product":"linux_kernel","vendor":"linux"}],"cvss":{"score":7.8,"severity":"high","source":"cna","vector":"CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H","version":"3.1"},"cwes":[{"id":"CWE-416","name":"Use After Free"}],"description":"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        \u003c--- ERROR\n        jffs2_clear_xattr_subsystem    \u003c--- free\n    jffs2_clear_xattr_subsystem        \u003c--- 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.","ecosystems":[],"exploits":{"exploitdb":0,"first_seen":null,"github_poc":0,"max_poc_stars":null,"metasploit":0,"nuclei":0,"refs":[],"tier":"none_known"},"has_fix":true,"headline":"jffs2: fix use-after-free in jffs2_clear_xattr_subsystem","id":"CVE-2021-47656","indexable":true,"kev":null,"kind":"cve","links":{"ecosystem":null,"product":"linux:linux_kernel","products":["linux:linux_kernel"],"type":"use_after_free","year":"2021"},"n_packages":0,"n_references":9,"next":{"headline":"drm/virtio: Ensure that objs is not NULL in virtio_gpu_array_put_free()","id":"CVE-2021-47657"},"packages":[],"prev":{"headline":"media: venus: vdec: fixed possible memory leak issue","id":"CVE-2021-47655"},"products":["Linux"],"published":"2025-02-26","related":[{"cvss_score":8.8,"headline":"Linux Kernel Out-of-Bounds Write","id":"CVE-2026-53266","kev_date_added":"2026-09-18","published":"2026-06-25"},{"cvss_score":8.8,"headline":"Linux Kernel Improper Input Validation","id":"CVE-2013-6282","kev_date_added":"2022-09-15","published":"2013-11-19"},{"cvss_score":8.4,"headline":"Linux Kernel Heap-Based Buffer Overflow","id":"CVE-2022-0185","kev_date_added":"2024-08-21","published":"2022-02-11"},{"cvss_score":8.4,"headline":"Linux Kernel Privilege Escalation","id":"CVE-2013-2094","kev_date_added":"2022-09-15","published":"2013-05-14"},{"cvss_score":7.8,"headline":"Linux Kernel Unspecified","id":"CVE-2026-53362","kev_date_added":"2026-08-27","published":"2026-07-04"},{"cvss_score":7.8,"headline":"Linux Kernel Missing Initialization of a Variable","id":"CVE-2026-46300","kev_date_added":"2026-10-28","published":"2026-05-23"},{"cvss_score":7.8,"headline":"Linux Kernel Race Condition","id":"CVE-2025-39964","kev_date_added":"2026-09-18","published":"2025-10-13"}],"sources":[{"class":"attribution","licence":"CVE Terms of Use (MITRE)","name":"CVE List","prefix":"CVE"},{"class":"attribution","licence":"US public information, NVD API terms","name":"NVD"},{"class":"attribution","licence":"CWE Terms of Use","name":"CWE (MITRE)"},{"class":"attribution","licence":"FIRST CVSS licence","name":"CVSS (FIRST)"}],"ssvc":{"automatable":"no","exploitation":"none","technical_impact":"total"},"state":"PUBLISHED","updated":"2026-08-05","vendors":["Linux"]},"summary":"A use-after-free vulnerability in the Linux kernel's JFFS2 filesystem allows attackers to cause a denial of service or potentially execute code via a crafted image.","url":"https://insights.sbomify.com/CVE-2021-47656/"}