CVE-2025-39792 dm: Always split write BIOs to zoned device limits

What is CVE-2025-39792?

CVE-2025-39792 is a high-severity denial of service vulnerability in Linux kernel, published on 12 Sep 2025. 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:

dm: Always split write BIOs to zoned device limits

Any zoned DM target that requires zone append emulation will use the block layer zone write plugging. In such case, DM target drivers must not split BIOs using dm_accept_partial_bio() as doing so can potentially lead to deadlocks with queue freeze operations. Regular write operations used to emulate zone append operations also cannot be split by the target driver as that would result in an invalid writen sector value return using the BIO sector.

In order for zoned DM target drivers to avoid such incorrect BIO splitting, we must ensure that large BIOs are split before being passed to the map() function of the target, thus guaranteeing that the limits for the mapped device are not exceeded.

dm-crypt and dm-flakey are the only target drivers supporting zoned devices and using dm_accept_partial_bio().

In the case of dm-crypt, this function is used to split BIOs to the internal max_write_size limit (which will be suppressed in a different patch). However, since crypt_alloc_buffer() uses a bioset allowing only up to BIO_MAX_VECS (256) vectors in a BIO. The dm-crypt device max_segments limit, which is not set and so default to BLK_MAX_SEGMENTS (128), must thus be respected and write BIOs split accordingly.

In the case of dm-flakey, since zone append emulation is not required, the block layer zone write plugging is not used and no splitting of BIOs required.

Modify the function dm_zone_bio_needs_split() to use the block layer helper function bio_needs_zone_write_plugging() to force a call to bio_split_to_limits() in dm_split_and_process_bio(). This allows DM target drivers to avoid using dm_accept_partial_bio() for write operations on zoned DM devices.

Which versions are affected by CVE-2025-39792?

It affects 1 product.

Products include Linux kernel.

How do I fix CVE-2025-39792?

Apply the vendor's patch.

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-2025-39792 being exploited?

There is no known exploitation of CVE-2025-39792 in the wild and no public exploit code.

Other vulnerabilities in Linux kernel

• CVE-2026-53266 Linux Kernel Out-of-Bounds Write Exploited High 8.8
• CVE-2013-6282 Linux Kernel Improper Input Validation Exploited High 8.8
• CVE-2022-0185 Linux Kernel Heap-Based Buffer Overflow Exploited High 8.4
• CVE-2013-2094 Linux Kernel Privilege Escalation Exploited High 8.4
• CVE-2026-53362 Linux Kernel Unspecified Exploited High 7.8

All Linux kernel vulnerabilities

Sources

• CVE record
• NVD
• OSV
• GitHub advisory
• How this page is made

Also known as BELL-CVE-2025-39792, DEBIAN-CVE-2025-39792, GHSA-2r9w-6jgj-8pc5, UBUNTU-CVE-2025-39792.