Look up another CVE · open CVE-2026-52959 in the interactive tracker
CVE-2026-52959
virt: sev-guest: Do not use host-controlled page order in cleanup path
Published 2026-06-24 (4 months ago) by the Linux kernel CNA. Subsystem drivers/virt. Debian urgency: unimportant.
What to do, per Debian release
Debian's own status for CVE-2026-52959 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 | not affected | 6.12.113-1 | Nothing to do. trixie never shipped the vulnerable code. |
| Debian 14forky | fixed | 7.0.10-1 | Update the kernel and reboot. Fixed in 7.0.10-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.0.10-1 | Update the kernel and reboot. Fixed in 7.0.10-1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
When issuing an extended guest request (SVM_VMGEXIT_EXT_GUEST_REQUEST), get_ext_report() allocates a buffer to retrieve a certificate blob from the host, keeping track of its size in report_req->certs_len. However, the host may return SNP_GUEST_VMM_ERR_INVALID_LEN, indicating an invalid buffer size, as well as the expected length of such buffer. get_ext_report() subsequently updates report_req->certs_len with the host-controlled value, and cleans up the buffer by computing a page order from such value. This is incorrect, as the host-provided length may not match the page order of the original allocation, potentially resulting in corruption in the page allocator. Fix this by using alloc_pages_exact() instead, and reusing @npages to compute the size passed to free_pages_exact(). For consistency, also use @npages to compute the size when allocating the pages, even though this last change has no functional effect.
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/virt/coco/sev-guest/sev-guest.c
- What this is
- THE RESTMAINTAINERS section matched on */ · linux-kernel@vger.kernel.org · Buried alive in reporters
- Kernel module
- sev_guest
Check it on the machine
grep -wE 'CONFIG_SEV_GUEST|CONFIG_VIRT_DRIVERS' /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 sev_guestPrints 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 amd64/cloud-amd64, arm64/arm64, arm64/cloud-arm64, arm64/rt/arm64, armhf/armmp, armhf/armmp-lpae, armhf/rt/armmp, i386/686, i386/686-pae, i386/rt/686-pae, ppc64el/powerpc64le
- trixieMnot built on arm64/arm64, arm64/arm64-16k, arm64/cloud-arm64, arm64/rt/arm64, armel/rpi, armhf/armmp, armhf/armmp-lpae, armhf/rt/armmp, ppc64el/powerpc64le, ppc64el/powerpc64le-64k, riscv64/riscv64, s390x/s390x
- forky, sidMnot built on arm64/arm64, arm64/arm64-16k, arm64/cloud-arm64, arm64/rt-arm64, 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_SEV_GUEST, CONFIG_VIRT_DRIVERS
- 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
- 2026-06-24 (4 months ago)source
- CVSS
- 7.8 high
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:Hsource recompute it - Attack vector
- local (AV:L)source
- EPSS
- 0.11%, higher than 1.3% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- unimportantsource
- Subsystem
- drivers/virt
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 6.14 | 6.18.33 | 3f6fb0211b39 |
| 6.14 | 7.0.10 | 9e48b4f813d2 |
| 6.14 | 7.1 | 23e6a1ca04ae |
| 6.13.8 | 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:LAttack vector, local
- The vulnerable path is reached through local guest interfaces, primarily the /dev/sev-guest SNP_GET_EXT_REPORT ioctl and the TSM configfs report path. It is not directly reachable by network packets, adjacent protocols, or physical device insertion.
- AC:LAttack complexity, low
- There is no race or fragile timing requirement; the caller can request an undersized certificate buffer and the VMM can deterministically return INVALID_LEN with a mismatched npages value. The resulting wrong-order free occurs synchronously in cleanup.
- PR:LPrivileges required, low
- The driver performs no capable() or namespace privilege check before dispatching SNP_GET_EXT_REPORT; exploitation only requires access to the local attestation interface. Because device-node policy may grant non-root attestation access, the higher-severity low-privilege value is appropriate.
- UI:NUser interaction, none
- No victim human action is required once a local process or attestation agent issues the request. The corrupted cleanup path is triggered automatically by the VMM response.
- S:UScope, unchanged
- The corrupted memory is guest kernel page-allocator state governed by the vulnerable guest kernel itself. This is best modeled as kernel memory corruption within the same security authority, not a guest-to-host escape.
- C:HConfidentiality impact, high
- The wrong-order __free_pages() can return unrelated in-use pages to the allocator, creating page aliasing and plausible arbitrary kernel memory disclosure. Under the required overestimate rule, allocator corruption is treated as high confidentiality impact.
- I:HIntegrity impact, high
- Freeing more pages than were allocated can let later allocations overlap live kernel objects, providing a plausible write/control-flow corruption primitive. This supports high integrity impact rather than treating the bug as a mere cleanup error.
- A:HAvailability impact, high
- Page allocator corruption can immediately trigger warnings, bad-page detection, oopses, or later kernel crashes. A repeatable local request can therefore cause high availability impact.