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CVE-2026-72356
cifs: Fix missing credit release on failure in cifs_issue_read()
Published 2026-08-15 (2 months ago) by the Linux kernel CNA. Subsystem fs/smb. Debian urgency: unimportant.
What to do, per Debian release
Debian's own status for CVE-2026-72356 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 | not affected | 6.1.190-1 | Nothing to do. bookworm never shipped the vulnerable code. |
| Debian 13trixie | fixed | 6.12.100-1 | Update the kernel and reboot. Fixed in 6.12.100-1. A running kernel keeps the old code until the machine restarts. |
| Debian 14forky | fixed | 7.1.5-1 | Update the kernel and reboot. Fixed in 7.1.5-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.1.5-1 | Update the kernel and reboot. Fixed in 7.1.5-1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
Fix missing release of credits in the failure path in cifs_issue_read() lest retrying the subreq just overwrites the credits value.
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/file.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
- 2026-08-15 (2 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
- 0.63%, higher than 49.1% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- unimportantsource
- 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 |
|---|---|---|
| 6.10 | 6.12.97 | b9ee1f0347bf |
| 6.10 | 6.18.40 | 86652704a7fd |
| 6.10 | 7.1.5 | 3a303f985c6b |
| 6.10 | 7.2 | c16b8c4cfb4f |
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 bug is in the CIFS/SMB client read path reached over TCP/445 when netfs issues reads; a malicious or compromised remote SMB server can provoke replayable async_readv failures (-EAGAIN/-ECONNABORTED) after credits are reserved, matching prior client-side CIFS credit CVEs scored as Network.
- AC:LAttack complexity, low
- The remote server controls both sides of the retry: it can reset the connection or force reconnects to return replayable errors, and netfs reissues the same subrequest deterministically; no race or memory-layout condition outside attacker control is required.
- PR:NPrivileges required, none
- The attacker is the remote SMB peer and needs no account, credentials, or local privileges on the victim; exploitation occurs during normal read/writeback I/O on an already-established CIFS mount (fstab, autofs, Azure Files, enterprise NAS).
- UI:NUser interaction, none
- Once a CIFS mount exists, the server triggers the flaw by its responses to client-initiated reads with no further victim interaction; mounting is a deployment precondition, not an action required at exploit time per kernel CNA convention for client filesystem bugs.
- S:UScope, unchanged
- Impact is confined to SMB credit/in_flight accounting and I/O scheduling within the client kernel; it does not cross VM, IOMMU, or sandbox security boundaries.
- C:NConfidentiality impact, none
- The flaw leaks SMB protocol credits and misaccounts counters; it does not read or disclose kernel memory, user data, or pointers, and provides no information-disclosure primitive.
- I:NIntegrity impact, none
- No memory corruption, type confusion, or arbitrary write occurs; the only effect is permanently losing credits from the server pool when a failed read subrequest is retried without releasing them first.
- A:HAvailability impact, high
- Each leaked credit permanently depletes server->credits; repeated retries exhaust the pool until smb2_wait_mtu_credits blocks all CIFS I/O on that connection in uninterruptible waits, causing system-wide hang/DoS for processes using the mount.