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CVE-2026-74690
s390/ism: Fix UAF of sba and ieq during ism_dev_exit()
Published 2026-08-22 (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-2026-74690 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 | 7.1.9-1 | Update the kernel and reboot. Fixed in 7.1.9-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.1.9-1 | Update the kernel and reboot. Fixed in 7.1.9-1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
A ism interrupt handler can be active in parallel with ism_dev_exit(), accessing freed data structures. No new interrupts will be generated after unregister_ieq(). Drain ongoing interrupt handlers by free_irq(), before freeing ism data structures.
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/net/ism_drv.c
- What this is
- NETWORKING DRIVERSMAINTAINERS section matched on drivers/s390/net/ · netdev@vger.kernel.org · Maintained
Check it on the machine
grep -wE 'CONFIG_ISM|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 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_ISM, 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
- 2026-08-22 (2 months ago)source
- CVSS
- 8.4 high
CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:Hsource recompute it - Attack vector
- local (AV:L)source
- EPSS
- 0.19%, higher than 8.4% 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 |
|---|---|---|
| 4.19 | 6.18.45 | fc3021284050 |
| 4.19 | 7.1.9 | 774394d27930 |
| 4.19 | 7.2 | b1896543ce59 |
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 UAF is opened in ism_dev_exit() during local PCI/driver teardown (ism_remove on module unload, sysfs unbind, or hot-unplug); remote SMC-D peers can raise ISM IRQs but cannot alone reach the freeing path that creates the dangling sba/ieq pointers.
- AC:LAttack complexity, low
- This is a classic UAF race where the attacker controls the IRQ side by sustaining SMC-D move_data/signal_event traffic (or timing rmmod/unbind) while teardown frees sba/ieq before free_irq(); no uncontrollable memory layout or rare config is required on IBM Z ISM deployments.
- PR:NPrivileges required, none
- Privileged teardown opens the window, but the concurrent UAF dereference is performed by ISM IRQ handlers servicing SMC-D traffic from unprivileged local socket users or remote LPAR peers that need no credentials or capabilities on the victim LPAR, only SMC connectivity.
- UI:NUser interaction, none
- No victim interaction is required beyond normal automated ISM interrupt processing during driver removal; an attacker only needs to keep SMC-D sessions active (or flood them) while the ISM device is torn down during maintenance, module unload, or hot-unplug.
- S:UScope, unchanged
- Impact is kernel heap/DMA-coherent memory corruption and privilege escalation within the host/LPAR kernel; it does not cross a VM, hypervisor, IOMMU, or other security-authority boundary.
- C:HConfidentiality impact, high
- ism_handle_irq() and ism_handle_event() read freed PAGE_SIZE sba and ieq DMA buffers (dmb_bits, dmbe_mask, event entries) after dma_free_coherent(), enabling sprayable slab reuse and arbitrary kernel memory disclosure per UAF guidance.
- I:HIntegrity impact, high
- The IRQ handler writes to freed sba fields (summary/event bits, dmbe_mask clears) and then calls dibs client handle_irq/handle_event with attacker-influenced SMC state, providing heap grooming and control-flow hijack primitives from the UAF.
- A:HAvailability impact, high
- Concurrent access to freed sba/ieq in hardirq reliably causes kernel oops/panic during ISM teardown on active SMC-D workloads, and UAF guidance treats any ISM interrupt-time use-after-free as high availability impact even before full exploitation.