CVE-2026-74738 regmap: sdw-mbq: don't call an unset readable_reg callback
A null pointer dereference in the Linux kernel's regmap SoundWire driver allows local attackers to cause a system crash.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-74738?
CVE-2026-74738 is a vulnerability in Linux, published on 26 Aug 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Official description
In the Linux kernel, the following vulnerability has been resolved:
regmap: sdw-mbq: don't call an unset readable_reg callback
regmap_sdw_mbq_poll_busy() decides whether to poll the Function Busy bit by calling ctx->readable_reg(), which is a straight copy of config->readable_reg. That callback is optional: regmap_readable() treats a NULL ->readable_reg as "every register is readable", and drivers rely on that. es9356 and tac5xx2-sdw both build an MBQ regmap without one.
Since commit ca1b11b36d82 ("regmap: sdw-mbq: Allow defers on undeferrable controls") the poll runs on every -ENODATA, not only for Controls the driver marked deferrable, so any of those devices answering COMMAND_IGNORED takes the kernel through a NULL function pointer.
Treat a missing callback the way the rest of regmap does and poll.
Which versions are affected by CVE-2026-74738?
How do I fix CVE-2026-74738?
Apply the vendor's patch.
Is CVE-2026-74738 being exploited?
There is no known exploitation of CVE-2026-74738 in the wild and no public exploit code.
Sources
Also known as BELL-CVE-2026-74738, DEBIAN-CVE-2026-74738, UBUNTU-CVE-2026-74738.