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CVE-2026-80544
s390/zcrypt: Improve EP11 CPRB domain handling with ASN.1 parsing
Published 2026-08-26 (2 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-2026-80544 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 | 7.1.10-1 | Update the kernel and reboot. Fixed in 7.1.10-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.1.10-1 | Update the kernel and reboot. Fixed in 7.1.10-1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
The zcrypt_msgtype6_send_ep11_cprb() function uses fragile struct overlays to access and modify the domain field in the EP11 CPRB payload, creating maintainability and security concerns: 1. Struct overlay approach (pld_hdr) assumes fixed payload structure and doesn't validate the actual ASN.1 encoding. 2. Complex length format detection logic is error-prone and doesn't properly validate bounds at each parsing step. 3. Direct struct member access bypasses proper ASN.1 validation. Fix by replacing struct overlays with explicit ASN.1 parsing that validates each field (payload tag/length, function tag/length/value, optional domain tag/length/value) with proper bounds checking at every step. Add asn1_int_encode() helper function to safely write integer values with correct endianness conversion. This makes the code consistent with the validation pattern introduced with the rework of the xcrb_msg_to_type6_ep11cprb_msgx() function.
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/zcrypt_msgtype6.c
- What this is
- S390 ZCRYPT AND PKEY DRIVER AND AP BUSMAINTAINERS section matched on drivers/s390/crypto/ · linux-s390@vger.kernel.org · Supported
- Kernel module
- zcrypt
Check it on the machine
grep -wE '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.
lsmod | grep -w zcryptPrints 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 does not build this code in 1 release. It does build it in 3 releases, so the answer depends on which release the machine runs.
- bookwormn
- trixieMnot built on amd64/amd64, amd64/cloud-amd64, amd64/rt/amd64, 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
- forky, sidMnot built on amd64/amd64, amd64/cloud-amd64, amd64/rt-amd64, 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
- n
- not enabled on any flavour - this release does not build the code
- M
- a module where it is built at all; some flavours do not build it
- Build switches
- 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
- 2026-08-26 (2 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
- 0.18%, higher than 7.4% 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 |
|---|---|---|
| 6.18.57 | 6.18.57 | 00a44ff06bcf |
| 7.1 | 7.1.10 | db21b2cf6dd0 |
| 7.1 | 7.2 | 0864a163783b |
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 bug is reached only via the ZSENDEP11CPRB ioctl on /dev/z90crypt (or a zcrypt class device node), following zcrypt_unlocked_ioctl() -> zsendep11cprb_ioctl() -> _zcrypt_send_ep11_cprb() -> zcrypt_msgtype6_send_ep11_cprb(); there is no network, USB, or remote packet path.
- AC:LAttack complexity, low
- After prep_ep11_ap_msg() ASN.1 validation, an attacker can reliably trigger the flaw with a minimal non-management EP11 CPRB whose payload omits the domain field or uses variable ASN.1 length encodings; the overlay then writes dom_val at a miscalculated offset with no races or victim-dependent state.
- PR:LPrivileges required, low
- The ioctl path performs only ap_perms bitmask checks (ioctl/card/queue masks default to all permitted) and no capability or real-root gate; any local user who can open the zcrypt character device can send crafted EP11 CPRBs, which is standard unprivileged local access on s390 systems with crypto hardware.
- UI:NUser interaction, none
- Exploitation requires only the attacker's own ioctl with attacker-controlled CPRB data; no separate victim action such as mounting a filesystem or opening a file is needed beyond the attacker's direct device access.
- S:UScope, unchanged
- The out-of-bounds write corrupts kernel heap memory inside the zcrypt driver's AP message buffer within the same kernel security domain; it does not cross a VM, container, or IOMMU boundary to impact a separate authority.
- C:HConfidentiality impact, high
- The unchecked struct overlay can write four bytes past the validated ASN.1 payload boundary inside a kernel-allocated AP message buffer; such heap corruption is exploitable for kernel memory disclosure and is scored as high confidentiality impact per memory-corruption guidance.
- I:HIntegrity impact, high
- zcrypt_msgtype6_send_ep11_cprb() performs an out-of-bounds 32-bit write of AP_QID_QUEUE() via payload_hdr->dom_val when ASN.1 layout does not match the assumed fixed pld_hdr overlay, enabling heap corruption and potential arbitrary kernel code execution.
- A:HAvailability impact, high
- Writing past the validated EP11 CPRB payload into kernel heap memory can cause immediate kernel oops/panic or sustained denial of service through repeated ioctl-triggered corruption on IBM Z systems using EP11 crypto adapters.