In the Linux kernel, the following vulnerability has been resolved:
netfs: Fix netfs_create_write_req() to handle async cache object creation
netfs_create_write_req() will skip caching if the fscache cookie is
disabled, but this is a problem because async cache object creation might
not have got far enough yet that has been enabled - thereby causing the
call to fscache_begin_write_operation() to be skipped.
Fix this by removing the checks on the cookie and delegating this to
fscache_begin_write_operation().
CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
CVSS Score: 9.8
AV:N - The bug is in netfs client write/cache coordination for CIFS, NFS+fscache, Ceph, AFS, and 9p. A malicious remote filesystem server can deliver file data and control protocol timing to drive async fscache object creation and subsequent kernel writeback over the network.
AC:L - The attacker controls both sides of the race by interleaving reads and writes or triggering writeback while the fscache cookie is still in CREATING/LOOKING_UP; the async-creation window can be hit reliably with retries, not conditions outside attacker influence.
PR:N - A malicious NFS/SMB/Ceph server needs no privileges on the victim client; once a fscache-enabled mount to that server exists, exploitation requires only ordinary file access or automated writeback, not real root or init-namespace capabilities.
UI:N - After a triggering read from the remote server, kernel writeback can invoke netfs_writepages without further victim action; an attacker with file access can also drive the race directly through concurrent read/write syscalls.
S:U - Impact is kernel heap/folio corruption during local pagecache I/O within the same kernel security authority; it does not inherently cross VM, container, IOMMU, or sandbox boundaries.
C:H - Skipping fscache_begin_write_operation desynchronizes cache and writeback streams; the same netfs/fscache subsystem previously produced UAFs when PG_private_2 coordination failed, enabling disclosure via freed/reused folio memory.
I:H - Inconsistent dual-stream write completion can free or reuse folios while still referenced, yielding heap corruption primitives that related netfs fscache bugs have leveraged for arbitrary kernel writes and privilege escalation.
A:H - The related netfs fscache fix documented kernel oops, ceph caps warnings, RCU expedited stalls, and UAF crashes from this coordination failure class; skipping required cache setup can oops, panic, or hang the system during writeback.
| Attack Vector |
Network |
Scope |
Unchanged |
| Attack Complexity |
Low |
Confidentiality Impact |
High |
| Privileges Required |
None |
Integrity Impact |
High |
| User Interaction |
None |
Availability Impact |
High |
AV:N - The bug is in netfs client write/cache coordination for CIFS, NFS+fscache, Ceph, AFS, and 9p. A malicious remote filesystem server can deliver file data and control protocol timing to drive async fscache object creation and subsequent kernel writeback over the network.
AC:L - The attacker controls both sides of the race by interleaving reads and writes or triggering writeback while the fscache cookie is still in CREATING/LOOKING_UP; the async-creation window can be hit reliably with retries, not conditions outside attacker influence.
PR:N - A malicious NFS/SMB/Ceph server needs no privileges on the victim client; once a fscache-enabled mount to that server exists, exploitation requires only ordinary file access or automated writeback, not real root or init-namespace capabilities.
UI:N - After a triggering read from the remote server, kernel writeback can invoke netfs_writepages without further victim action; an attacker with file access can also drive the race directly through concurrent read/write syscalls.
S:U - Impact is kernel heap/folio corruption during local pagecache I/O within the same kernel security authority; it does not inherently cross VM, container, IOMMU, or sandbox boundaries.
C:H - Skipping fscache_begin_write_operation desynchronizes cache and writeback streams; the same netfs/fscache subsystem previously produced UAFs when PG_private_2 coordination failed, enabling disclosure via freed/reused folio memory.
I:H - Inconsistent dual-stream write completion can free or reuse folios while still referenced, yielding heap corruption primitives that related netfs fscache bugs have leveraged for arbitrary kernel writes and privilege escalation.
A:H - The related netfs fscache fix documented kernel oops, ceph caps warnings, RCU expedited stalls, and UAF crashes from this coordination failure class; skipping required cache setup can oops, panic, or hang the system during writeback.
CVSS 3.1