In the Linux kernel, the following vulnerability has been resolved:
f2fs: read COW data with the original inode during atomic write
When updating an atomic-write file, f2fs_write_begin() may read the
previously written data back from the COW inode:
prepare_atomic_write_begin() locates the block in the COW inode and sets
use_cow, and the read bio is then built with the COW inode:
f2fs_submit_page_read(use_cow ? F2FS_I(inode)->cow_inode : inode,
...);
and f2fs_grab_read_bio() decides whether to schedule fs-layer decryption
(STEP_DECRYPT) for the bio based on that inode via
fscrypt_inode_uses_fs_layer_crypto().
However, the folio being filled belongs to the original inode
(folio->mapping->host == inode), and the data stored in the COW block was
encrypted (or left as plaintext) using the original inode's context, not
the COW inode's -- see f2fs_encrypt_one_page(), which keys off
fio->page->mapping->host. fscrypt_decrypt_pagecache_blocks() likewise
operates on folio->mapping->host.
The COW inode is created as a tmpfile in the parent directory and inherits
its encryption policy from there. With test_dummy_encryption the newly
created COW inode gets the dummy policy and becomes encrypted, while a
pre-existing regular file -- created before the policy applied, e.g.
already present in the on-disk image -- stays unencrypted. The read
path then sets STEP_DECRYPT based on the encrypted COW inode and calls
fscrypt_decrypt_pagecache_blocks() on a folio whose host (the unencrypted
original inode) has a NULL ->i_crypt_info, dereferencing it:
Oops: general protection fault, probably for non-canonical address ...
KASAN: null-ptr-deref in range [0x0000000000000008-0x000000000000000f]
RIP: 0010:fscrypt_decrypt_pagecache_blocks+0xa0/0x310
Workqueue: f2fs_post_read_wq f2fs_post_read_work
Call Trace:
fscrypt_decrypt_bio+0x1eb/0x340
f2fs_post_read_work+0xba/0x140
process_one_work+0x91c/0x1a40
worker_thread+0x677/0xe90
kthread+0x2bc/0x3a0
The COW inode is only needed to locate the on-disk block, and that block
address is already resolved into @blkaddr by prepare_atomic_write_begin()
via __find_data_block(cow_inode, ...); f2fs_submit_page_read() then reads
from that physical @blkaddr directly, so the inode argument only selects
the post-read crypto context, not which block is fetched. Reading with
@inode therefore returns the same (latest, not-yet-committed) COW data,
while making both the fs-layer decryption decision and the inline crypto
path use the correct (original inode's) key.
With the COW inode no longer used at the read site, the use_cow flag has no
remaining consumer; drop it from f2fs_write_begin() and
prepare_atomic_write_begin().
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.NVD CVSS v3 · CVSS v3.0 or v3.1
- EG Likelihood
- <0.1% within 30 daysSource: FIRST EPSS. 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