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CVE-2026-64558
s390/pkey: Check length in pkey_pckmo handler implementation
Published 2026-07-29 (3 months ago) by the Linux kernel CNA. Subsystem drivers/s390. Debian urgency: unimportant.
What to do, per Debian release
Debian's own status for CVE-2026-64558 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 | fixedDSA-6405-1 · 2026-07-31 · text | 6.12.100-1 | Update the kernel and reboot. DSA-6405-1 shipped the fix on 2026-07-31, 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. |
| Debian 12bookworm · linux-6.12 | fixedDLA-4724-1 · 2026-08-07 · text | 6.12.100-1~deb12u1 | Update the kernel and reboot. DLA-4724-1 shipped the fix on 2026-08-07, in 6.12.100-1~deb12u1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
Explicitly check the length of the target buffer in the pkey_pckmo implementation of the key_to_protkey() handler function. The handler function fails, if the generated output data exceeds the length of the provided target buffer.
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/s390/crypto/pkey_pckmo.c
- What this is
- S390 ZCRYPT AND PKEY DRIVER AND AP BUSMAINTAINERS section matched on drivers/s390/crypto/ · linux-s390@vger.kernel.org · Supported
Check it on the machine
grep -wE 'CONFIG_PKEY_PCKMO|CONFIG_S390' /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.
Show whether Debian builds this, per release
Debian does not build this code in 4 releases. The build rule could not be established for 1 release, so nothing is claimed about those.
- bookworm?
- trixie, forky, sid, bookworm · linux-6.12n
- ?
- not established - no Makefile entry for the affected file
- n
- not enabled on any flavour - this release does not build the code
Where a release above reads "not established", no build rule for the affected file was found in that release's kernel tree. That is a gap in this lookup, not a finding that the code is absent.
- Build switches
- CONFIG_PKEY_PCKMO, CONFIG_S390
- 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
- 2026-07-29 (3 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
- 0.12%, higher than 1.7% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- unimportantsource
- Subsystem
- drivers/s390
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 6.12 | 6.12.97 | 02028a24e26d |
| 6.12 | 6.18.40 | 433e5e70cdc1 |
| 6.12 | 7.1.5 | 614aa0491c7a |
| 6.12 | 7.2 | 1ac287e2af9a |
Debian advisories
| Advisory | Date | Shipped to | Debian |
|---|---|---|---|
| DLA-4724-1 | 2026-08-07 | bookworm 6.12.100-1~deb12u1 | tracker |
| DSA-6405-1 | 2026-07-31 | trixie 6.12.100-1 | tracker |
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 entered through the PKEY_KBLOB2PROTK/PKEY_KBLOB2PROTK2 ioctls on the /dev/pkey character device, or via an AF_ALG setkey on the paes skciphers. Both require local system access; no network input reaches this code.
- AC:LAttack complexity, low
- A single ioctl with a hand-crafted 176-byte protected-key token (type 0x00, version TOKVER_PROTECTED_KEY, keytype PKEY_KEYTYPE_HMAC_1024, len 160) deterministically triggers the 96-byte overflow; there is no race, no memory-layout dependency, and no hardware or wrapping-key prerequisite since the non-AES branch skips pckmo_verify_protkey().
- PR:LPrivileges required, low
- /dev/pkey is registered as a miscdevice with .mode = 0666 and pkey_unlocked_ioctl() contains no capability or permission check, so any unprivileged local user can reach the bug; the paes/AF_ALG setkey path likewise requires no privileges.
- UI:NUser interaction, none
- The attacker triggers the overflow entirely on their own via a single ioctl or socket option call; no victim action, mount, or file open is involved.
- S:UScope, unchanged
- The corruption is confined to the kernel's own stack within the same security authority; exploitation yields kernel privilege escalation rather than crossing a VM, IOMMU, or sandbox boundary.
- C:HConfidentiality impact, high
- The attacker gains a fully controlled 96-byte out-of-bounds stack write that can clobber adjacent locals, saved pointers and return addresses, which is readily leveraged into arbitrary kernel memory disclosure; the copy also leaves *protkeylen inflated to 160 while the buffer is 64 bytes, feeding an oversized length back to callers.
- I:HIntegrity impact, high
- This is an out-of-bounds write of 96 attacker-chosen bytes past the end of a kernel stack object (the last member of struct pkey_kblob2pkey), overwriting saved registers and the return address — a classic control-flow hijack / local privilege escalation primitive.
- A:HAvailability impact, high
- Smashing the kernel stack past the canary reliably produces a stack-protector panic or an oops on return, and any unprivileged user can repeat it at will to crash the machine.