In the Linux kernel, the following vulnerability has been resolved:
ext4: fix use-after-free read in ext4_find_extent for bigalloc + inline
Syzbot found the following issue:
loop0: detected capacity change from 0 to 2048
EXT4-fs (loop0): mounted filesystem 00000000-0000-0000-0000-000000000000 without journal. Quota mode: none.
==================================================================
BUG: KASAN: use-after-free in ext4_ext_binsearch_idx fs/ext4/extents.c:768 [inline]
BUG: KASAN: use-after-free in ext4_find_extent+0x76e/0xd90 fs/ext4/extents.c:931
Read of size 4 at addr ffff888073644750 by task syz-executor420/5067
CPU: 0 PID: 5067 Comm: syz-executor420 Not tainted 6.2.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/26/2022
Call Trace:
__dump_stack lib/dump_stack.c:88 [inline]
dump_stack_lvl+0x1b1/0x290 lib/dump_stack.c:106
print_address_description+0x74/0x340 mm/kasan/report.c:306
print_report+0x107/0x1f0 mm/kasan/report.c:417
kasan_report+0xcd/0x100 mm/kasan/report.c:517
ext4_ext_binsearch_idx fs/ext4/extents.c:768 [inline]
ext4_find_extent+0x76e/0xd90 fs/ext4/extents.c:931
ext4_clu_mapped+0x117/0x970 fs/ext4/extents.c:5809
ext4_insert_delayed_block fs/ext4/inode.c:1696 [inline]
ext4_da_map_blocks fs/ext4/inode.c:1806 [inline]
ext4_da_get_block_prep+0x9e8/0x13c0 fs/ext4/inode.c:1870
ext4_block_write_begin+0x6a8/0x2290 fs/ext4/inode.c:1098
ext4_da_write_begin+0x539/0x760 fs/ext4/inode.c:3082
generic_perform_write+0x2e4/0x5e0 mm/filemap.c:3772
ext4_buffered_write_iter+0x122/0x3a0 fs/ext4/file.c:285
ext4_file_write_iter+0x1d0/0x18f0
call_write_iter include/linux/fs.h:2186 [inline]
new_sync_write fs/read_write.c:491 [inline]
vfs_write+0x7dc/0xc50 fs/read_write.c:584
ksys_write+0x177/0x2a0 fs/read_write.c:637
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x3d/0xb0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x63/0xcd
RIP: 0033:0x7f4b7a9737b9
RSP: 002b:00007ffc5cac3668 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007f4b7a9737b9
RDX: 00000000175d9003 RSI: 0000000020000200 RDI: 0000000000000004
RBP: 00007f4b7a933050 R08: 0000000000000000 R09: 0000000000000000
R10: 000000000000079f R11: 0000000000000246 R12: 00007f4b7a9330e0
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
Above issue is happens when enable bigalloc and inline data feature. As
commit 131294c35ed6 fixed delayed allocation bug in ext4_clu_mapped for
bigalloc + inline. But it only resolved issue when has inline data, if
inline data has been converted to extent(ext4_da_convert_inline_data_to_extent)
before writepages, there is no EXT4_STATE_MAY_INLINE_DATA flag. However
i_data is still store inline data in this scene. Then will trigger UAF
when find extent.
To resolve above issue, there is need to add judge "ext4_has_inline_data(inode)"
in ext4_clu_mapped().
What the EG score is made of (scorer v4.0: the three questions the 0–10 score mixes, published apart · methodology)
The EG score (7.8): severity, escalated by confirmed exploitation. This CVE's 7.8 is its impact severity (EG Severity), not escalated.
- EG Severity
- 7.8 HIGHCVSS-B, impact only: no KEV listing, EPSS or EG-KEV tier raises it.GitHub Security Advisory CVSS
- EG Likelihood
- 0.2% within 30 daysSource: FIRST EPSS (model v2026.06.15, score date 2026-11-04). FIRST's exploitation probability, not an EchelonGraph model.
- Confirmed exploitation
- None on record (CISA KEV, EG-KEV Tier 1)Reported apart from the likelihood: an observed fact, not a probability.
- EG Priority
- SSVC Track at medium mission impactTrack at low or medium mission impact; Track* at high (mission-essential systems).CISA BOD 26-04: 14 days if the affected system is publicly exposed; Fix on system upgrade if it is not.Each input and its source, and whom BOD 26-04 binds: the SSVC and BOD 26-04 blocks below.
SSVC (CISA's decision table, applied by EchelonGraph)Track at low or medium mission impact; Track* at high (mission-essential systems).
A fix is available. Apply it within your standard update timelines.
Exploitation none (no CISA value, KEV listing or exploit code on record) · Automatable no (CISA's BOD 26-04 default) · Technical impact total (CISA's BOD 26-04 default). EchelonGraph holds no SSVC assessment of this CVE from CISA: none of these inputs is from Vulnrichment. EchelonGraph applied CISA's decision table to them; CISA publishes SSVC inputs and the table, not a decision for each CVE. Mission impact is CISA's Mission & Well-being decision point, and only you can judge it. CISA's table makes it high when Mission Prevalence is Essential — the vulnerable component "directly provides capabilities that constitute at least one MEF for at least one entity" (MEF: mission essential function) — or when Public Well-Being Impact is Irreversible: "multiple fatalities are likely", the cyber-physical system "is likely lost or destroyed", "extreme or serious externalities" are imposed on other parties, or social systems such as elections or the financial grid "are destabilized and potentially collapse". CISA's decision table
BOD 26-04 (CISA's remediation timeline, Table 1)14 days if the affected system is publicly exposed; Fix on system upgrade if it is not.
The score's inputs: In CISA KEV no (CISA's KEV catalog) · Automatable no (CISA's BOD 26-04 default) · Technical impact total (CISA's BOD 26-04 default). Where an input reads “CISA's BOD 26-04 default”, no one has published it for this CVE, and CISA's implementation guidance says: “If “Automatable” and “Technical Impact” information items about a CVE ID are not available and the CVE ID is not in the KEV Catalog, CISA will treat its values as “no” and “total,” respectively, until CISA or a third party provides metadata about the CVE ID. CISA will always provide the Vulnrichment data for a CVE ID listed in the KEV Catalog.” Whether your system is publicly exposed is yours to answer. BOD 26-04 binds US Federal Civilian Executive Branch agencies; for anyone else it is CISA's published timeline, a reference rather than an obligation. The directive · how EchelonGraph applies it