CVE-2025-21745 blk-cgroup: Fix class @block_class's subsystem refcount leakage

What is CVE-2025-21745?

CVE-2025-21745 is a medium-severity denial of service vulnerability in Linux kernel, published on 27 Feb 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:

blk-cgroup: Fix class @block_class's subsystem refcount leakage

blkcg_fill_root_iostats() iterates over @block_class's devices by class_dev_iter_(init|next)(), but does not end iterating with class_dev_iter_exit(), so causes the class's subsystem refcount leakage.

Fix by ending the iterating with class_dev_iter_exit().

Which versions are affected by CVE-2025-21745?

It affects 1 product.

Products include Linux kernel.

How do I fix CVE-2025-21745?

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-2025-21745 being exploited?

There is no known exploitation of CVE-2025-21745 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 AZL-57902, BELL-CVE-2025-21745, DEBIAN-CVE-2025-21745, GHSA-hfgc-7c7c-g6r6, ROOT-OS-UBUNTU-2404-CVE-2025-21745, UBUNTU-CVE-2025-21745.