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CVE-2026-74401
dlm: fix add msg handle in send_queue ordered
Published 2026-08-15 (2 months ago) by the Linux kernel CNA. Subsystem fs/dlm. Debian urgency: not yet assigned.
What to do, per Debian release
Debian's own status for CVE-2026-74401 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 | 6.12.100-1 | 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
In a benchmark scenario triggering a lot of requests that triggers a lot of DLM messages on the network it can be that the mh->seq is not ordered according the oldest seq number. This ordering is required by dlm_receive_ack as "before(mh->seq, seq)" will stop to check for older sequence numbers that are ordered in the tail of "node->send_queue". The side effects of not having it correct ordered regarding "before(mh->seq, seq)" are refcounting issues and use-after free. I only was able to reproduce this issue in a experimental DLM branch and a user space DLM benchmark that uses io_uring. After changing this I don't experienced any refcounting with the sending buffer issues anymore.
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/dlm/midcomms.c
- What this is
- DISTRIBUTED LOCK MANAGER (DLM)MAINTAINERS section matched on fs/dlm/ · gfs2@lists.linux.dev · Supported
- Kernel module
- dlm
Check it on the machine
grep -w CONFIG_DLM /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 dlmPrints 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, but not on every flavour. At least one release below builds the code on some of its kernel flavours and not on others, so the answer depends on the architecture and flavour installed.
- bookworm, trixie, forky, sidMnot built on amd64/cloud-amd64, arm64/cloud-arm64
- M
- a module where it is built at all; some flavours do not build it
- Build switch
- CONFIG_DLM
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
- 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
- 0.65%, higher than 50.2% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- not yet assignedsource
- Subsystem
- fs/dlm
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 5.14 | 6.6.145 | ae9e534e502a |
| 5.14 | 6.12.97 | 6369619f1b66 |
| 5.14 | 6.18.40 | 712714f818d8 |
| 5.14 | 7.1.5 | 4d45250b1d22 |
| 5.14 | 7.2 | d2248cb70c07 |
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 UAF is triggered in dlm_receive_ack when processing DLM_ACK packets from remote cluster peers over lowcomms TCP/SCTP port 21064 (receive_from_sock -> dlm_process_incoming_buffer -> dlm_midcomms_receive_buffer_3_2); wire ACK sequence numbers directly drive premature dlm_mhandle_delete on the victim.
- AC:LAttack complexity, low
- The send_queue ordering race in midcomms_new_msg_cb is hit under heavy concurrent DLM traffic; an attacker controls both sides by flooding lock requests from a cluster peer (io_uring benchmark per fix author) while sending ACKs, without depending on timing they cannot influence.
- PR:NPrivileges required, none
- DLM has no authentication or TLS; the only gate is source IP matching a configured cluster node in addr_to_nodeid. A compromised cluster peer or attacker on the cluster network needs no Unix account or local privileges on the victim to deliver crafted DLM_ACK packets.
- UI:NUser interaction, none
- No victim user action is required; ACKs and lock traffic are processed automatically on already-running HA cluster nodes (GFS2/OCFS2/Pacemaker) by DLM receive and send workqueues without any interactive step.
- S:UScope, unchanged
- Impact is confined to kernel heap and refcount corruption within the victim node's kernel address space; no VM, IOMMU, or sandbox boundary is crossed—standard kernel UAF enabling privilege escalation on the same host.
- C:HConfidentiality impact, high
- Misordered send_queue causes dlm_receive_ack to skip or prematurely free mhandles via call_rcu/dlm_mhandle_release while references still exist; UAF reads from freed slab objects enable heap grooming and arbitrary kernel memory disclosure.
- I:HIntegrity impact, high
- Premature dlm_mhandle_delete releases in-flight mh->msg buffers and corrupts kref counts while commit paths still dereference the handle; UAF write primitives via reclaimed slab data can hijack kernel control flow per DLM UAF scoring guidance.
- A:HAvailability impact, high
- Refcounting corruption and use-after-free in dlm_receive_ack reliably cause KASAN splats, kernel oopses, and cluster-wide availability loss when DLM on HA nodes handling GFS2/OCFS2 lock traffic crashes or hangs.