In the Linux kernel, the following vulnerability has been resolved:
ext4: fix null-ptr-deref in ext4_write_info
I caught a null-ptr-deref bug as follows:
==================================================================
KASAN: null-ptr-deref in range [0x0000000000000068-0x000000000000006f]
CPU: 1 PID: 1589 Comm: umount Not tainted 5.10.0-02219-dirty #339
RIP: 0010:ext4_write_info+0x53/0x1b0
[...]
Call Trace:
dquot_writeback_dquots+0x341/0x9a0
ext4_sync_fs+0x19e/0x800
__sync_filesystem+0x83/0x100
sync_filesystem+0x89/0xf0
generic_shutdown_super+0x79/0x3e0
kill_block_super+0xa1/0x110
deactivate_locked_super+0xac/0x130
deactivate_super+0xb6/0xd0
cleanup_mnt+0x289/0x400
__cleanup_mnt+0x16/0x20
task_work_run+0x11c/0x1c0
exit_to_user_mode_prepare+0x203/0x210
syscall_exit_to_user_mode+0x5b/0x3a0
do_syscall_64+0x59/0x70
entry_SYSCALL_64_after_hwframe+0x44/0xa9
==================================================================
Above issue may happen as follows:
-------------------------------------
exit_to_user_mode_prepare
task_work_run
__cleanup_mnt
cleanup_mnt
deactivate_super
deactivate_locked_super
kill_block_super
generic_shutdown_super
shrink_dcache_for_umount
dentry = sb->s_root
sb->s_root = NULL <--- Here set NULL
sync_filesystem
__sync_filesystem
sb->s_op->sync_fs > ext4_sync_fs
dquot_writeback_dquots
sb->dq_op->write_info > ext4_write_info
ext4_journal_start(d_inode(sb->s_root), EXT4_HT_QUOTA, 2)
d_inode(sb->s_root)
s_root->d_inode <--- Null pointer dereference
To solve this problem, we use ext4_journal_start_sb directly
to avoid s_root being used.
What the EG score is made of (scorer v4.0: the three questions the 0–10 score mixes, published apart · methodology)
The EG score (5.5): severity, escalated by confirmed exploitation. This CVE's 5.5 is its impact severity (EG Severity), not escalated.
- EG Severity
- 5.5 MEDIUMCVSS-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 2026-10-17). 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 every mission impact level.CISA BOD 26-04: 60 days if the affected system is publicly exposed; Fix on system upgrade if it is not.Each input and its source: the SSVC and BOD 26-04 blocks below.
SSVC (CISA's decision table, applied by EchelonGraph)Track at every mission impact level.
A fix is available. Apply it within your standard update timelines.
Exploitation none (CISA Vulnrichment) · Automatable no (CISA Vulnrichment) · Technical impact partial (CISA Vulnrichment). All three are CISA's SSVC values (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)60 days if the affected system is publicly exposed; Fix on system upgrade if it is not.
In CISA KEV no (CISA's KEV catalog) · Automatable no (CISA Vulnrichment) · Technical impact partial (CISA Vulnrichment). 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