{"cve":"CVE-2025-37856","nvd":{"published":"2025-05-09T07:16:06.593","modified":"2026-10-21T13:18:06.667","status":"Modified","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nbtrfs: harden block_group::bg_list against list_del() races\n\nAs far as I can tell, these calls of list_del_init() on bg_list cannot\nrun concurrently with btrfs_mark_bg_unused() or btrfs_mark_bg_to_reclaim(),\nas they are in transaction error paths and situations where the block\ngroup is readonly.\n\nHowever, if there is any chance at all of racing with mark_bg_unused(),\nor a different future user of bg_list, better to be safe than sorry.\n\nOtherwise we risk the following interleaving (bg_list refcount in parens)\n\nT1 (some random op)                       T2 (btrfs_mark_bg_unused)\n                                        !list_empty(&bg->bg_list); (1)\nlist_del_init(&bg->bg_list); (1)\n                                        list_move_tail (1)\nbtrfs_put_block_group (0)\n                                        btrfs_delete_unused_bgs\n                                             bg = list_first_entry\n                                             list_del_init(&bg->bg_list);\n                                             btrfs_put_block_group(bg); (-1)\n\nUltimately, this results in a broken ref count that hits zero one deref\nearly and the real final deref underflows the refcount, resulting in a WARNING.","cvss_v4":null,"cvss_v3":{"version":"3.1","vector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H","score":5.5},"cwes":[],"references":["https://git.kernel.org/stable/c/185fd73e5ac06027c4be9a129e59193f6a3ef202","https://git.kernel.org/stable/c/7511e29cf1355b2c47d0effb39e463119913e2f6","https://git.kernel.org/stable/c/9039afe6240ae01d6caf2fa731590ac74fb8a69b","https://git.kernel.org/stable/c/909e60fb469d4101c6b08cf6e622efb062bb24a1","https://git.kernel.org/stable/c/bf089c4d1141b27332c092b1dcca5022c415a3b6"],"products":["linux:linux_kernel"],"source":"nvd","synced_at":"2026-10-22T16:41:11.231219466+00:00"},"epss":{"cve":"CVE-2025-37856","score":0.00308,"percentile":0.23437,"date":"2026-10-25"},"kev":null,"osv":[],"attribution":["This product uses the NVD API but is not endorsed or certified by the NVD.","EPSS scores: FIRST Exploit Prediction Scoring System, https://www.first.org/epss","Known exploited vulnerabilities: CISA Known Exploited Vulnerabilities Catalog, https://www.cisa.gov/known-exploited-vulnerabilities-catalog","Package advisories: OSV (https://osv.dev), from the GitHub Advisory Database, PyPA, Go, RustSec and other ecosystem databases, under CC-BY 4.0 or CC0","CVE records: the CVE Program's CVE List (https://www.cve.org), under its terms of use (https://www.cve.org/Legal/TermsOfUse). CVE is a registered trademark of The MITRE Corporation; this product is not affiliated with the CVE Program."]}