EUVD-2026-38908
GHSA-4j7p-pwp5-4v56
Severity by source
AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:H
Local trigger via ioctl on a mounted crafted image (AV:L, PR:L, AC:L); OOB read leaks kernel memory (C:H) and can panic (A:H); no integrity impact and no scope change.
Primary rating from Vendor (Linux).
CVSS VectorVendor: Linux
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:H
Lifecycle Timeline
5DescriptionCVE.org
In the Linux kernel, the following vulnerability has been resolved:
ocfs2: validate bg_bits during freefrag scan
[BUG] A crafted filesystem can trigger an out-of-bounds bitmap walk when OCFS2_IOC_INFO is issued with OCFS2_INFO_FL_NON_COHERENT.
BUG: KASAN: use-after-free in instrument_atomic_read include/linux/instrumented.h:68 [inline] BUG: KASAN: use-after-free in _test_bit include/asm-generic/bitops/instrumented-non-atomic.h:141 [inline] BUG: KASAN: use-after-free in test_bit_le include/asm-generic/bitops/le.h:21 [inline] BUG: KASAN: use-after-free in ocfs2_info_freefrag_scan_chain fs/ocfs2/ioctl.c:495 [inline] BUG: KASAN: use-after-free in ocfs2_info_freefrag_scan_bitmap fs/ocfs2/ioctl.c:588 [inline] BUG: KASAN: use-after-free in ocfs2_info_handle_freefrag fs/ocfs2/ioctl.c:662 [inline] BUG: KASAN: use-after-free in ocfs2_info_handle_request+0x1c66/0x3370 fs/ocfs2/ioctl.c:754 Read of size 8 at addr ffff888031bce000 by task syz.0.636/1435 Call Trace: __dump_stack lib/dump_stack.c:94 [inline] dump_stack_lvl+0xbe/0x130 lib/dump_stack.c:120 print_address_description mm/kasan/report.c:378 [inline] print_report+0xd1/0x650 mm/kasan/report.c:482 kasan_report+0xfb/0x140 mm/kasan/report.c:595 check_region_inline mm/kasan/generic.c:186 [inline] kasan_check_range+0x11c/0x200 mm/kasan/generic.c:200 __kasan_check_read+0x11/0x20 mm/kasan/shadow.c:31 instrument_atomic_read include/linux/instrumented.h:68 [inline] _test_bit include/asm-generic/bitops/instrumented-non-atomic.h:141 [inline] test_bit_le include/asm-generic/bitops/le.h:21 [inline] ocfs2_info_freefrag_scan_chain fs/ocfs2/ioctl.c:495 [inline] ocfs2_info_freefrag_scan_bitmap fs/ocfs2/ioctl.c:588 [inline] ocfs2_info_handle_freefrag fs/ocfs2/ioctl.c:662 [inline] ocfs2_info_handle_request+0x1c66/0x3370 fs/ocfs2/ioctl.c:754 ocfs2_info_handle+0x18d/0x2a0 fs/ocfs2/ioctl.c:828 ocfs2_ioctl+0x632/0x6e0 fs/ocfs2/ioctl.c:913 vfs_ioctl fs/ioctl.c:51 [inline] __do_sys_ioctl fs/ioctl.c:597 [inline] __se_sys_ioctl fs/ioctl.c:583 [inline] __x64_sys_ioctl+0x197/0x1e0 fs/ioctl.c:583 ...
[CAUSE] ocfs2_info_freefrag_scan_chain() uses on-disk bg_bits directly as the bitmap scan limit. The coherent path reads group descriptors through ocfs2_read_group_descriptor(), which validates the descriptor before use. The non-coherent path uses ocfs2_read_blocks_sync() instead and skips that validation, so an impossible bg_bits value can drive the bitmap walk past the end of the block.
[FIX] Compute the bitmap capacity from the filesystem format with ocfs2_group_bitmap_size(), report descriptors whose bg_bits exceeds that limit, and clamp the scan to the computed capacity. This keeps the freefrag report going while avoiding reads beyond the buffer.
AnalysisAI
Out-of-bounds memory read in the Linux kernel's OCFS2 filesystem driver allows a local user to leak kernel memory or crash the system by issuing the OCFS2_IOC_INFO ioctl with the OCFS2_INFO_FL_NON_COHERENT flag against a crafted or malicious OCFS2 image. The non-coherent freefrag scan path trusts the on-disk bg_bits group-descriptor field as a bitmap limit without validation, driving the bitmap walk past the end of the block buffer. …
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Attack ChainAIDerived
Hypothetical attack flow derived from CVE metadata
Vulnerability AssessmentAI
| Exploitation | Exploitation requires local access and the ability to have a maliciously crafted OCFS2 filesystem mounted, then invoking the OCFS2_IOC_INFO ioctl with the OCFS2_INFO_FL_NON_COHERENT flag set - the non-coherent path is the specific trigger, because the coherent path validates group descriptors and is not affected. … Additional conditions and limiting factors are described in the full assessment. |
| Risk Assessment | The CVSS 3.1 base score is 7.1 (AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:H), reflecting a local, low-complexity, low-privilege bug with high confidentiality (kernel memory disclosure) and high availability (KASAN-detected use-after-free/OOB read can panic the kernel) impact and no integrity impact. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in. |
| Exploit Scenario | A low-privileged local user crafts an OCFS2 image with an out-of-range bg_bits group-descriptor value, gets it mounted (e.g. via a USB device on a host that auto-mounts, or on a system permitting unprivileged mounts), then calls the OCFS2_IOC_INFO ioctl with OCFS2_INFO_FL_NON_COHERENT to trigger the unvalidated freefrag bitmap walk, reading kernel memory beyond the buffer to leak data or panic the kernel. … |
| Remediation | Apply the vendor-released patch by upgrading to a fixed kernel for your branch: 5.10.258, 5.15.209, 6.1.175, 6.6.141, 6.12.91, 6.18.33, 7.0.10, or mainline 7.1 or later (the fix adds ocfs2_group_bitmap_size() validation, rejects descriptors whose bg_bits exceeds capacity, and clamps the scan). … Detailed patch versions, workarounds, and compensating controls in full report. |
Recommended ActionAI
24 hours: Audit inventory to identify Linux systems with OCFS2 filesystems mounted. …
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Same weakness CWE-416 – Use After Free
View allSame technique Buffer Overflow
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External POC / Exploit Code
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