CVE-2026-15923 Infinite loop denial of service in Zephyr SDIO byte-I/O from a card-supplied zero max_blk_size
A malicious SDIO card can cause an infinite loop and permanent denial of service in Zephyr RTOS by reporting a zero block size.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- None listed
What is CVE-2026-15923?
CVE-2026-15923 is a medium-severity denial of service vulnerability in zephyrproject zephyr, published on 14 Sep 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Official description
The Zephyr SDIO subsystem function sdio_io_rw_extended_helper() in subsys/sd/sdio.c finishes transfers with a byte-I/O loop that uses size = MIN(remaining, func->cis.max_blk_size) as the per-iteration step. The value func->cis.max_blk_size is decoded directly from the SDIO card's CIS FUNCE tuple in sdio_decode_cis() and is not validated. When a card reports a maximum block size of zero, size is always 0, remaining never decreases, and the loop spins forever.
The loop is reached from the public SDIO client API used by drivers, including sdio_read_fifo(), sdio_write_fifo(), and the incrementing register read/write helpers, each of which enters the loop while holding the per-card mutex func->card->lock. A card advertising max_blk_size == 0 therefore hangs the calling thread permanently on its first non-block-aligned transfer and never releases the mutex, denying service to the SDIO peripheral (and any subsystem such as Wi-Fi that depends on it) until the device is reset.
The malicious value must come from the SDIO card itself, so the defect is exploitable where a removable SDIO/combo card slot lets an attacker insert a crafted or malfunctioning card (a physical attack vector); on boards with a soldered SDIO peripheral it is not attacker-influenceable. There is no memory-safety, confidentiality, or integrity impact — only a permanent availability loss. The fix returns -EIO when func->cis.max_blk_size is zero, before the loop is entered.
Weakness: CWE-835
Which versions are affected by CVE-2026-15923?
How do I fix CVE-2026-15923?
No fix has been published for CVE-2026-15923 yet. Limit exposure of the affected software until one is available.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-15923 being exploited?
There is no known exploitation of CVE-2026-15923 in the wild and no public exploit code.
Sources
Also known as GHSA-4pvm-wrcp-jjf5.