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CVE-2024-50285
ksmbd: check outstanding simultaneous SMB operations
Published 2024-11-19 (23 months ago) by the Linux kernel CNA. Subsystem fs/smb. Debian urgency: not yet assigned.
What to do, per Debian release
Debian's own status for CVE-2024-50285 in every release this site tracks, and what each one means in practice. Every status below is the one the Debian Security Team publishes for this CVE. source
| Release | Status | Version | What this means |
|---|---|---|---|
| Debian 12bookworm | vulnerable | 6.1.190-1 | No fix published anywhere yet, neither in Debian nor upstream for the series bookworm tracks. Watch the Debian tracker page for this CVE. Advisories for bookworm have historically landed a median of 23 days after publication. |
| Debian 13trixie | fixed | 6.11.9-1 | Update the kernel and reboot. Fixed in 6.11.9-1. A running kernel keeps the old code until the machine restarts. |
| Debian 14forky | fixed | 6.11.9-1 | Update the kernel and reboot. Fixed in 6.11.9-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 6.11.9-1 | Update the kernel and reboot. Fixed in 6.11.9-1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
If Client send simultaneous SMB operations to ksmbd, It exhausts too much memory through the "ksmbd_work_cache”. It will cause OOM issue. ksmbd has a credit mechanism but it can't handle this problem. This patch add the check if it exceeds max credits to prevent this problem by assuming that one smb request consumes at least one credit.
Where it lives
The fix touches these files. If the subsystem is one you do not use, the practical exposure is lower, though the package is still the vulnerable one.
fs/smb/server/connection.c
fs/smb/server/connection.h
fs/smb/server/server.c
fs/smb/server/smb_common.c
fs/smb/server/smb_common.h
- What this is
- KERNEL SMB3 SERVER (KSMBD)MAINTAINERS section matched on fs/smb/server/ · linux-cifs@vger.kernel.org · Maintained
- Kernel module
- ksmbd
Check it on the machine
grep -wE 'CONFIG_SMBFS|CONFIG_SMB_SERVER' /boot/config-$(uname -r)Reads the booted kernel's own configuration, on the machine and nowhere else. =y is built in, =m is a module, and an is not set line means the code is not there.
lsmod | grep -w ksmbdPrints a line if that module is loaded right now, and nothing if it is not. One that is not loaded can still be loaded later by anything that needs it.
Show whether Debian builds this, per release
Debian builds this as a loadable module. Every release below compiles it as a module on every flavour, so whether the code is in the running kernel depends on whether that module is loaded.
- bookworm, trixie, forky, sidm
- m
- a loadable module on every flavour - check lsmod, can be blacklisted
- Build switches
- CONFIG_SMBFS, CONFIG_SMB_SERVER
- Reads as
- all on means the file is compiled; any one off means it is not.
From the configuration Debian publishes for every kernel flavour it builds. It covers only the architectures Debian ships a linux-config package for, and nothing about a kernel you built yourself. Debian's own status above stays authoritative about the source package.MAINTAINERS kbuild Makefiles Debian linux-config packages
Signals
- Published
- 2024-11-19 (23 months ago)source
- CVSS
- 7.5 high
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:Hsource recompute it - Attack vector
- network (AV:N)source
- EPSS
- 0.60%, higher than 47.5% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- not yet assignedsource
- Subsystem
- fs/smb
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 5.15 | 6.6.61 | 1f993777275c |
| 5.15 | 6.11.8 | e257ac6fe138 |
| 5.15 | 6.12 | 0a77d947f599 |
Why the CNA scored it this way
Quoted from the kernel CNA's own scoring file, word for word. A highlighted metric carries the most severe value CVSS v3.1 defines for it, which is what pushes the score up. source
- AV:NAttack vector, network
- ksmbd is the in-kernel SMB server; the vulnerable allocation is driven directly by PDUs read off the TCP/445 socket in `ksmbd_conn_handler_loop()`. Any remote host with network reachability to the server triggers it.
- AC:LAttack complexity, low
- The attacker simply pipelines SMB PDUs faster than the workqueue drains them, optionally stalling workers by not draining its own socket; there is no race to win and no memory layout to control. Success is deterministic and repeatable.
- PR:NPrivileges required, none
- The allocation in `queue_ksmbd_work()` happens before any negotiate, session setup, or authentication — the only gate is `ksmbd_smb_request()`, which checks the protocol magic bytes alone. An entirely unauthenticated attacker reaches it on connect.
- UI:NUser interaction, none
- The attacker initiates the TCP connection and sends the request flood unaided; no action by any local user or administrator is required.
- S:UScope, unchanged
- Memory exhaustion occurs within the kernel's own security authority on the ksmbd server host, with no crossing of a VM, IOMMU, or sandbox boundary.
- C:NConfidentiality impact, none
- The flaw is unbounded allocation of `ksmbd_work` objects and request buffers; no attacker-controlled read, out-of-bounds access, or uninitialized data is exposed, and the fix adds only a counter check.
- I:NIntegrity impact, none
- No memory corruption, out-of-bounds write, or type confusion is involved — the queued objects are correctly allocated and freed, just in unbounded quantity, so no data is modified.
- A:HAvailability impact, high
- An unauthenticated client can exhaust kernel memory through `ksmbd_work_cache` plus attacker-sized request buffers, driving the system into OOM as stated in the commit message, killing processes and rendering the host unusable.