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CVE-2026-68453
s390/zcrypt: Fix buffer over-read in cca_cipher2protkey
Published 2026-08-13 (2 months ago) by the Linux kernel CNA. Subsystem drivers/s390. Debian urgency: not yet assigned.
Debian does not build this code. The per-release build detail is under "Where it lives" below.
What to do, per Debian release
Debian's own status for CVE-2026-68453 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 | vulnerable | 6.12.113-1 | No fix published anywhere yet, neither in Debian nor upstream for the series trixie tracks. Watch the Debian tracker page for this CVE. Advisories for trixie have historically landed a median of 11 days after publication. |
| Debian 14forky | fixed | 7.1.8-1 | Update the kernel and reboot. Fixed in 7.1.8-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.1.8-1 | Update the kernel and reboot. Fixed in 7.1.8-1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
Add validation of both the actual key buffer size and token length fields in all the cca_check_sec*token() functions. Additionally check in cca_gencipherkey() for possible underflow with returned key size. The CCA token structures contain user-controlled len fields that were used in operations without proper validation against both the actual buffer size and minimum token structure size. An attacker could set this field larger than the actual buffer size, leading to reading beyond buffer boundaries. This may result in a kernel crash or exposure of memory via sending this as part of a request down to the crypto card. Also an attacker could have used a very small len value and thus enforce a buffer under-run which may produce similar effects as a over-read. So now a key must - key buf length must be at least sizeof the token struct - the key len field inside the token must fit into the range of sizeof key token struct ... key buf length
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_cca.c
drivers/s390/crypto/zcrypt_ccamisc.c
drivers/s390/crypto/zcrypt_ccamisc.h
- 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_CCA|CONFIG_S390|CONFIG_ZCRYPT' /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 below, every kernel flavour Debian publishes has the switch off, so the vulnerable file is compiled into no kernel binary Debian ships.
- bookworm, trixie, forky, sidn
- n
- not enabled on any flavour - this release does not build the code
- Build switches
- CONFIG_PKEY_CCA, CONFIG_S390, CONFIG_ZCRYPT
- 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
- 2026-08-13 (2 months ago)source
- CVSS
- 7.1 high
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:Hsource recompute it - Attack vector
- local (AV:L)source
- EPSS
- 0.13%, higher than 2.1% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- not yet assignedsource
- 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 |
|---|---|---|
| 5.4 | 6.18.44 | a57fd7fcdb63 |
| 5.4 | 7.1.8 | 3b2abee2a678 |
| 5.4 | 7.2 | 36b230835b8a |
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 code is reached only through ioctls on the /dev/pkey misc device (PKEY_VERIFYKEY2, PKEY_KBLOB2PROTK2/3) or via in-kernel paes/dm-crypt setkey calls, all of which require local access to the s390 system. There is no network-facing consumer of CCA key tokens.
- AC:LAttack complexity, low
- The attacker fully controls both the allocation size (memdup_user of an attacker-chosen keylen, minimum 8 bytes) and the token header bytes, so the out-of-bounds read is triggered deterministically on every ioctl with no race, timing, or uncontrolled memory-layout dependency; the adjacent slab contents can be groomed with further 8-byte key blobs.
- PR:LPrivileges required, low
- pkey_api.c registers the misc device with .mode = 0666 and pkey_unlocked_ioctl() performs no capable()/CAP_* check whatsoever, so any unprivileged local user can open /dev/pkey and issue the affected ioctls; pkey_handler_request_modules() even auto-loads the pkey-cca handler on demand.
- UI:NUser interaction, none
- Exploitation is a self-contained sequence of ioctl() calls made by the attacker's own process; no action by any other user or administrator is required.
- S:UScope, unchanged
- The out-of-bounds read stays within the kernel's own address space and the impact is confined to the kernel security authority; no VM, IOMMU, or sandbox boundary is crossed.
- C:HConfidentiality impact, high
- An 8-byte key buffer causes reads up to ~48 bytes past the allocation into neighbouring slab objects; cca_verifykey() returns OOB bytes to userspace via *keybitsize and the checks form a byte oracle, while cca_gencipherkey() used an unvalidated len to copy far beyond the 512-byte CPRB param block into a user-visible buffer, and token data is also transmitted to the crypto adapter.
- I:NIntegrity impact, none
- The defect is purely an over-read/under-run of length fields; no out-of-bounds write, freed-object reuse, or type confusion occurs, so no kernel data can be modified through this path.
- A:HAvailability impact, high
- The commit message states the over-read "may result in a kernel crash"; reading tens of bytes past a minimally sized kmalloc object can fault or trip KASAN/KFENCE, and the unbounded copy in cca_gencipherkey can walk far outside the parameter block, oopsing the kernel from an unprivileged, endlessly repeatable ioctl.