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CVE-2025-37750
smb: client: fix UAF in decryption with multichannel
Published 2025-05-01 (18 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-2025-37750 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 | 6.12.25-1 | Update the kernel and reboot. Fixed in 6.12.25-1. A running kernel keeps the old code until the machine restarts. |
| Debian 14forky | fixed | 6.12.25-1 | Update the kernel and reboot. Fixed in 6.12.25-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 6.12.25-1 | Update the kernel and reboot. Fixed in 6.12.25-1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
After commit f7025d861694 ("smb: client: allocate crypto only for primary server") and commit b0abcd65ec54 ("smb: client: fix UAF in async decryption"), the channels started reusing AEAD TFM from primary channel to perform synchronous decryption, but that can't done as there could be multiple cifsd threads (one per channel) simultaneously accessing it to perform decryption. This fixes the following KASAN splat when running fstest generic/249 with 'vers=3.1.1,multichannel,max_channels=4,seal' against Windows Server 2022: BUG: KASAN: slab-use-after-free in gf128mul_4k_lle+0xba/0x110 Read of size 8 at addr ffff8881046c18a0 by task cifsd/986 CPU: 3 UID: 0 PID: 986 Comm: cifsd Not tainted 6.15.0-rc1 #1 PREEMPT(voluntary) Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-3.fc41 04/01/2014 Call Trace: <TASK> dump_stack_lvl+0x5d/0x80 print_report+0x156/0x528 ? gf128mul_4k_lle+0xba/0x110 ? __virt_addr_valid+0x145/0x300 ? __phys_addr+0x46/0x90 ? gf128mul_4k_lle+0xba/0x110 kasan_report+0xdf/0x1a0 ? gf128mul_4k_lle+0xba/0x110 gf128mul_4k_lle+0xba/0x110 ghash_update+0x189/0x210 shash_ahash_update+0x295/0x370 ? __pfx_shash_ahash_update+0x10/0x10 ? __pfx_shash_ahash_update+0x10/0x10 ? __pfx_extract_iter_to_sg+0x10/0x10 ? ___kmalloc_large_node+0x10e/0x180 ? __asan_memset+0x23/0x50 crypto_ahash_update+0x3c/0xc0 gcm_hash_assoc_remain_continue+0x93/0xc0 crypt_message+0xe09/0xec0 [cifs] ? __pfx_crypt_message+0x10/0x10 [cifs] ? _raw_spin_unlock+0x23/0x40 ? __pfx_cifs_readv_from_socket+0x10/0x10 [cifs] decrypt_raw_data+0x229/0x380 [cifs] ? __pfx_decrypt_raw_data+0x10/0x10 [cifs] ? __pfx_cifs_read_iter_from_socket+0x10/0x10 [cifs] smb3_receive_transform+0x837/0xc80 [cifs] ? __pfx_smb3_receive_transform+0x10/0x10 [cifs] ? __pfx___might_resched+0x10/0x10 ? __pfx_smb3_is_transform_hdr+0x10/0x10 [cifs] cifs_demultiplex_thread+0x692/0x1570 [cifs] ? __pfx_cifs_demultiplex_thread+0x10/0x10 [cifs] ? rcu_is_watching+0x20/0x50 ? rcu_lockdep_current_cpu_online+0x62/0xb0 ? find_held_lock+0x32/0x90 ? kvm_sched_clock_read+0x11/0x20 ? local_clock_noinstr+0xd/0xd0 ? trace_irq_enable.constprop.0+0xa8/0xe0 ? __pfx_cifs_demultiplex_thread+0x10/0x10 [cifs] kthread+0x1fe/0x380 ? kthread+0x10f/0x380 ? __pfx_kthread+0x10/0x10 ? local_clock_noinstr+0xd/0xd0 ? ret_from_fork+0x1b/0x60 ? local_clock+0x15/0x30 ? lock_release+0x29b/0x390 ? rcu_is_watching+0x20/0x50 ? __pfx_kthread+0x10/0x10 ret_from_fork+0x31/0x60 ? __pfx_kthread+0x10/0x10 ret_from_fork_asm+0x1a/0x30 </TASK>
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/client/cifsencrypt.c
fs/smb/client/smb2ops.c
fs/smb/client/smb2pdu.c
- What this is
- COMMON INTERNET FILE SYSTEM CLIENT (CIFS and SMB3)MAINTAINERS section matched on fs/smb/client/ · linux-cifs@vger.kernel.org · Supported
- Kernel module
- cifs
Check it on the machine
grep -wE 'CONFIG_CIFS|CONFIG_SMBFS' /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 cifsPrints 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_CIFS, CONFIG_SMBFS
- 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
- 2025-05-01 (18 months ago)source
- CVSS
- 9.8 critical
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:Hsource recompute it - Attack vector
- network (AV:N)source
- EPSS
- 0.38%, higher than 30.8% 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 |
|---|---|---|
| 6.12 | 6.12.24 | aa5a1e4b8829 |
| 6.12 | 6.13.12 | e859b216d946 |
| 6.12 | 6.14.3 | 950557922c12 |
| 6.12 | 6.15 | 9502dd5c7029 |
| 5.10.237 | 0 | 0 |
| 5.15.181 | 0 | 0 |
| 6.1.128 | 0 | 0 |
| 6.6.57 | 0 | 0 |
| 6.11.4 | 0 | 0 |
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
- The vulnerable decryption path is driven entirely by SMB3 transform PDUs received over TCP from the remote server, processed in the per-channel `cifsd` demultiplex thread; a malicious or compromised file server can additionally force the encrypted path on via `SMB2_SESSION_FLAG_ENCRYPT_DATA`/`SHI1005_FLAGS_ENCRYPT_DATA` and control response timing across all channels.
- AC:LAttack complexity, low
- The attacker controls both sides of the race — it chooses when to release encrypted responses on each of the N channels, and each response unconditionally calls `crypto_aead_setkey()` on the shared TFM; the race reproduced immediately under an ordinary fstest run against a stock Windows server, so no condition beyond the attacker's control is required.
- PR:NPrivileges required, none
- The attacker is the remote SMB peer and holds no credentials or account on the victim client; nothing on the path from socket receive to `crypt_message()` performs any capability or privilege check. The same corruption is also reachable by a wholly unprivileged local user issuing parallel I/O on the mount.
- UI:NUser interaction, none
- The mount is pre-existing deployment configuration (typically fstab/automount at boot), and once established the server triggers the bug purely by responding on multiple channels — no victim action is needed at attack time.
- S:UScope, unchanged
- The corruption is confined to the kernel heap of the client host; no VM, IOMMU, or sandbox boundary is crossed.
- C:HConfidentiality impact, high
- The UAF reads a freed kmalloc-4k `gf128mul_4k` table whose contents feed GHASH output transmitted to the server, and the concurrent `setkey` causes cross-session key confusion so data can be processed under another session's encryption key; a double-free of a 4K slab object further yields overlapping-allocation read primitives.
- I:HIntegrity impact, high
- Two concurrent `ghash_setkey()` calls can double-free the same `ctx->gf128` object, corrupting the kmalloc-4k freelist and giving two owners of one allocation — a well-established route to arbitrary write and control-flow hijack; plaintext may also be encrypted under the wrong session key.
- A:HAvailability impact, high
- The use-after-free and double-free corrupt slab metadata, producing oopses and panics (the reported KASAN slab-use-after-free); even absent full corruption, garbage GHASH state causes authentication-tag mismatches that tear down the connection into a reconnect loop.