In the Linux kernel, the following vulnerability has been resolved:
ntfs: avoid calling post_write_mst_fixup() for invalid index_block
ntfs_icx_ib_sync_write() calls post_write_mst_fixup() when ntfs_ib_write()
returns an error, intending to restore the buffer after a failed write.
However, ntfs_ib_write() returns an error immediately if
pre_write_mst_fixup() validation fails. The caller,
ntfs_icx_ib_sync_write(), interprets any error as a write failure
requiring rollback. It does not differentiate between I/O errors and
validation failures, and calls post_write_mst_fixup() anyway.
Since post_write_mst_fixup() assumes that the index_block contents is
correct, it doesn't perform the boundary checks, which results in
out-of-bounds memory access.
An attacker can craft a malicious NTFS image with:
- large index_block.usa_ofs offset, pointing outside the ntfs_record
- index_block.usa_count = 0, causing integer underflow
- or index_block.usa_count larger than actual number of sectors in the
ntfs_record, causing out-of-bounds access
KASAN reports describing the memory corruption:
==================================================================
BUG: KASAN: slab-out-of-bounds in post_write_mst_fixup+0x19c/0x1d0
Read of size 2 at addr ffff8881586c9018 by task p/9428
Call Trace:
dump_stack_lvl+0x100/0x190
print_report+0x139/0x4ad
? post_write_mst_fixup+0x19c/0x1d0
? __virt_addr_valid+0x262/0x500
? post_write_mst_fixup+0x19c/0x1d0
kasan_report+0xe4/0x1d0
? post_write_mst_fixup+0x19c/0x1d0
post_write_mst_fixup+0x19c/0x1d0
ntfs_icx_ib_sync_write+0x179/0x220
ntfs_inode_sync_filename+0x83d/0x1080
__ntfs_write_inode+0x1049/0x1480
ntfs_file_fsync+0x131/0x9b0
==================================================================
BUG: KASAN: slab-out-of-bounds in post_write_mst_fixup+0x1aa/0x1d0
Write of size 2 at addr ffff8881586c91fe by task p/9428
Call Trace:
dump_stack_lvl+0x100/0x190
print_report+0x139/0x4ad
? post_write_mst_fixup+0x1aa/0x1d0
? __virt_addr_valid+0x262/0x500
? post_write_mst_fixup+0x1aa/0x1d0
kasan_report+0xe4/0x1d0
? post_write_mst_fixup+0x1aa/0x1d0
post_write_mst_fixup+0x1aa/0x1d0
ntfs_icx_ib_sync_write+0x179/0x220
ntfs_inode_sync_filename+0x83d/0x1080
__ntfs_write_inode+0x1049/0x1480
ntfs_file_fsync+0x131/0x9b0
==================================================================
Let's move the post_write_mst_fixup() call to ntfs_ib_write().
The ntfs_ib_write() function calls pre_write_mst_fixup() at the beginning.
If the index_block contents is invalid, pre_write_mst_fixup() fails and
ntfs_ib_write() returns early without calling post_write_mst_fixup() on
bad index_block.
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 2026-10-27). 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