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CVE-2026-64034
net: mana: Fix TOCTOU double-fetch of hwc_msg_id from DMA buffer
Published 2026-07-19 (3 months ago) by the Linux kernel CNA. Subsystem drivers/net. Debian urgency: not yet assigned.
What to do, per Debian release
Debian's own status for CVE-2026-64034 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 | fixed | 6.1.176-1 | Update the kernel and reboot. Fixed in 6.1.176-1. A running kernel keeps the old code until the machine restarts. |
| Debian 13trixie | fixed | 6.12.94-1 | Update the kernel and reboot. Fixed in 6.12.94-1. A running kernel keeps the old code until the machine restarts. |
| Debian 14forky | fixed | 7.0.12-1 | Update the kernel and reboot. Fixed in 7.0.12-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.0.12-1 | Update the kernel and reboot. Fixed in 7.0.12-1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
In mana_hwc_rx_event_handler(), resp->response.hwc_msg_id is read from DMA-coherent memory and bounds-checked, then mana_hwc_handle_resp() re-reads the same field from the same DMA buffer for test_bit() and pointer arithmetic. DMA-coherent memory is mapped uncacheable on x86 and is shared, unencrypted, in Confidential VMs (SEV-SNP/TDX), so each load goes directly to host-visible memory. A H/W can modify the value between the check and the use, bypassing the bounds validation. Fix this by reading hwc_msg_id exactly once using READ_ONCE() into a stack-local variable in mana_hwc_rx_event_handler(), and passing the validated value as a parameter to mana_hwc_handle_resp().
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.
drivers/net/ethernet/microsoft/mana/hw_channel.c
- What this is
- Hyper-V/Azure CORE AND DRIVERSMAINTAINERS section matched on drivers/net/ethernet/microsoft/ · linux-hyperv@vger.kernel.org · Supported
- Kernel module
- mana
Check it on the machine
grep -wE 'CONFIG_ETHERNET|CONFIG_MICROSOFT_MANA|CONFIG_NET_VENDOR_MICROSOFT' /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 manaPrints 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.
- bookwormMnot built on armhf/armmp, armhf/armmp-lpae, armhf/rt/armmp, i386/686, i386/686-pae, i386/rt/686-pae, ppc64el/powerpc64le
- trixieMnot built on armel/rpi, armhf/armmp, armhf/armmp-lpae, armhf/rt/armmp, ppc64el/powerpc64le, ppc64el/powerpc64le-64k, riscv64/riscv64, s390x/s390x
- forky, sidMnot built on armhf/armmp, armhf/armmp-lpae, loong64/loong64, ppc64el/powerpc64le, ppc64el/powerpc64le-64k, riscv64/riscv64, s390x/s390x
- M
- a module where it is built at all; some flavours do not build it
- Build switches
- CONFIG_ETHERNET, CONFIG_MICROSOFT_MANA, CONFIG_NET_VENDOR_MICROSOFT
- 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
- 2026-07-19 (3 months ago)source
- CVSS
- 9.3 critical
CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:Hsource recompute it - Attack vector
- local (AV:L)source
- EPSS
- 0.11%, higher than 1.4% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- not yet assignedsource
- Subsystem
- drivers/net
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 5.13 | 5.15.209 | a201c66edf2e |
| 5.13 | 6.1.175 | 70ad2dff8d05 |
| 5.13 | 6.6.142 | 566f42fb67a7 |
| 5.13 | 6.12.92 | 6180a06bbc99 |
| 5.13 | 6.18.34 | 09ec063d87c2 |
| 5.13 | 7.0.11 | 3c4db56ccd13 |
| 5.13 | 7.1 | 35f0f0a2536a |
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:LAttack vector, local
- Exploitation requires a malicious hypervisor or host that can modify MANA HWC DMA-coherent response buffers between guest kernel loads; it is not reachable by sending network packets to the guest's data path.
- AC:LAttack complexity, low
- The attacker controlling the hypervisor fully controls DMA buffer contents and can reliably flip hwc_msg_id between the validation read and the use in mana_hwc_handle_resp() on uncacheable coherent memory.
- PR:NPrivileges required, none
- The attacking hypervisor needs no guest OS credentials or capabilities; exploitation targets the guest kernel through the virtual device DMA path while the MANA driver is active.
- UI:NUser interaction, none
- No victim user action is required beyond normal Azure VM operation with the MANA driver loaded and HWC receive buffers posted.
- S:CScope, changed
- The vulnerability crosses the VM/DMA security boundary by allowing a hostile hypervisor to corrupt guest kernel memory that the confidential-guest threat model assumes is protected from host tampering.
- C:HConfidentiality impact, high
- Out-of-bounds indexing via bypassed hwc_msg_id validation enables reading adjacent kernel heap objects through misdirected caller_ctx access and test_bit() on the inflight bitmap.
- I:HIntegrity impact, high
- Host-controlled response data is copied with memcpy() to an out-of-bounds output_buf pointer, enabling arbitrary kernel memory corruption and potential control-flow hijacking.
- A:HAvailability impact, high
- Out-of-bounds caller_ctx access and corrupted completion signaling can cause kernel oops, panic, or hang during HWC response handling.