CVE-2025-21754
Linux Kernel 6.5 – 6.6.78
Raw vector
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:HCVSS and EPSS are reproduced from their sources (NVD, FIRST EPSS). EPSS scores by FIRST (EPSS SIG), generated by Empirical Security. Risk Priority is our own derived reading, not an NVD score.
Summary
CVE-2025-21754 is a medium-severity Reachable Assertion (CWE-617) vulnerability in Linux Kernel. Its CVSS base score is 5.5 (Medium).
Operationally, exploitation aligns with the MITRE ATT&CK technique Exploitation for Defense Impairment (T1687); ranked at the 14th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.
The strongest mitigations our analysis identified map to SA-11 (Developer Testing and Evaluation) and SA-8 (Security and Privacy Engineering Principles) — see the control section below for these in your framework.
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2025-5154
Vulnerability Data
In the Linux kernel, the following vulnerability has been resolved: btrfs: fix assertion failure when splitting ordered extent after transaction abort If while we are doing a direct IO write a transaction abort happens, we mark all existing ordered extents…
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with the BTRFS_ORDERED_IOERR flag (done at btrfs_destroy_ordered_extents()), and then after that if we enter btrfs_split_ordered_extent() and the ordered extent has bytes left (meaning we have a bio that doesn't cover the whole ordered extent, see details at btrfs_extract_ordered_extent()), we will fail on the following assertion at btrfs_split_ordered_extent(): ASSERT(!(flags & ~BTRFS_ORDERED_TYPE_FLAGS)); because the BTRFS_ORDERED_IOERR flag is set and the definition of BTRFS_ORDERED_TYPE_FLAGS is just the union of all flags that identify the type of write (regular, nocow, prealloc, compressed, direct IO, encoded). Fix this by returning an error from btrfs_extract_ordered_extent() if we find the BTRFS_ORDERED_IOERR flag in the ordered extent. The error will be the error that resulted in the transaction abort or -EIO if no transaction abort happened. This was recently reported by syzbot with the following trace: FAULT_INJECTION: forcing a failure. name failslab, interval 1, probability 0, space 0, times 1 CPU: 0 UID: 0 PID: 5321 Comm: syz.0.0 Not tainted 6.13.0-rc5-syzkaller #0 Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014 Call Trace: <TASK> __dump_stack lib/dump_stack.c:94 [inline] dump_stack_lvl+0x241/0x360 lib/dump_stack.c:120 fail_dump lib/fault-inject.c:53 [inline] should_fail_ex+0x3b0/0x4e0 lib/fault-inject.c:154 should_failslab+0xac/0x100 mm/failslab.c:46 slab_pre_alloc_hook mm/slub.c:4072 [inline] slab_alloc_node mm/slub.c:4148 [inline] __do_kmalloc_node mm/slub.c:4297 [inline] __kmalloc_noprof+0xdd/0x4c0 mm/slub.c:4310 kmalloc_noprof include/linux/slab.h:905 [inline] kzalloc_noprof include/linux/slab.h:1037 [inline] btrfs_chunk_alloc_add_chunk_item+0x244/0x1100 fs/btrfs/volumes.c:5742 reserve_chunk_space+0x1ca/0x2c0 fs/btrfs/block-group.c:4292 check_system_chunk fs/btrfs/block-group.c:4319 [inline] do_chunk_alloc fs/btrfs/block-group.c:3891 [inline] btrfs_chunk_alloc+0x77b/0xf80 fs/btrfs/block-group.c:4187 find_free_extent_update_loop fs/btrfs/extent-tree.c:4166 [inline] find_free_extent+0x42d1/0x5810 fs/btrfs/extent-tree.c:4579 btrfs_reserve_extent+0x422/0x810 fs/btrfs/extent-tree.c:4672 btrfs_new_extent_direct fs/btrfs/direct-io.c:186 [inline] btrfs_get_blocks_direct_write+0x706/0xfa0 fs/btrfs/direct-io.c:321 btrfs_dio_iomap_begin+0xbb7/0x1180 fs/btrfs/direct-io.c:525 iomap_iter+0x697/0xf60 fs/iomap/iter.c:90 __iomap_dio_rw+0xeb9/0x25b0 fs/iomap/direct-io.c:702 btrfs_dio_write fs/btrfs/direct-io.c:775 [inline] btrfs_direct_write+0x610/0xa30 fs/btrfs/direct-io.c:880 btrfs_do_write_iter+0x2a0/0x760 fs/btrfs/file.c:1397 do_iter_readv_writev+0x600/0x880 vfs_writev+0x376/0xba0 fs/read_write.c:1050 do_pwritev fs/read_write.c:1146 [inline] __do_sys_pwritev2 fs/read_write.c:1204 [inline] __se_sys_pwritev2+0x196/0x2b0 fs/read_write.c:1195 do_syscall_x64 arch/x86/entry/common.c:52 [inline] do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83 entry_SYSCALL_64_after_hwframe+0x77/0x7f RIP: 0033:0x7f1281f85d29 RSP: 002b:00007f12819fe038 EFLAGS: 00000246 ORIG_RAX: 0000000000000148 RAX: ffffffffffffffda RBX: 00007f1282176080 RCX: 00007f1281f85d29 RDX: 0000000000000001 RSI: 0000000020000240 RDI: 0000000000000005 RBP: 00007f12819fe090 R08: 0000000000000000 R09: 0000000000000003 R10: 0000000000007000 R11: 0000000000000246 R12: 0000000000000002 R13: 0000000000000000 R14: 00007f1282176080 R15: 00007ffcb9e23328 </TASK> BTRFS error (device loop0 state A): Transaction aborted (error -12) BTRFS: error (device loop0 state A ---truncated---
- CWE(s)
Related Threats
MITRE ATT&CK Enterprise Techniques
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Affected Assets
Mitigating Controls
Mitigating Controls (NIST 800-53 r5) AI
Developer testing and evaluation finds reachable assertions during development.
Security engineering principles discourage use of assertions for handling untrusted input.
Validating untrusted inputs structurally prevents attacker data from reaching and triggering assertions.
Mitigating Controls (NIST CSF 2.0) AI
Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→CSF cross-walk (authority under review) — links open the control.
Secure SDLC practices directly prevent unsafe assertions from being coded in reachable paths.
Runtime monitoring of software can detect assertion-triggered crashes as adverse events.
Vulnerability identification processes can discover and record reachable-assertion flaws before deployment.
Mitigating Controls (ISO/IEC 27001:2022 Annex A) AI
Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→ISO cross-walk (authority under review) — links open the control.
Security testing in development can detect reachable assertions before release, reducing the likelihood of exploitation.
Secure coding standards explicitly ban the use of assert() or equivalent statements that can be triggered by external input.