Description
In the Linux kernel, the following vulnerability has been resolved:

blk-cgroup: fix UAF in __blkcg_rstat_flush()

When multiple blkgs in the same blkcg are released concurrently,
a use-after-free can occur. The race happens when one blkg's
__blkcg_rstat_flush() removes another blkg's iostat entries via
llist_del_all(). The second blkg sees an empty list and proceeds
to free itself while the first is still iterating over its entries.

Move the flush from __blkg_release() (RCU callback) to blkg_release()
(before call_rcu). This ensures the RCU grace period waits for any
concurrent flush's rcu_read_lock() section to complete before freeing.
Published: 2026-07-19
Score: 7.8 High
EPSS: < 1% Very Low
KEV: No
Impact: n/a
Action: n/a
AI Analysis

Impact

A use‑after‑free occurs in the blk‑cgroup subsystem of the Linux kernel when multiple block cgroup groups are released simultaneously. The first group’s __blkcg_rstat_flush() removes another group’s iostat entries while that entry is still being accessed, causing a kernel memory corruption. A local attacker could exploit this flaw to execute arbitrary code at ring 0, leading to full system compromise or privilege escalation.

Affected Systems

All systems running a Linux kernel that contains the unpatched blk‑cgroup code are potentially affected. The specific kernel releases are not listed in the CVE, so administrators should verify whether their running kernel incorporates the commits referenced in the CVE materials. The vulnerability affects the core Linux kernel and is not tied to a particular distribution.

Risk and Exploitability

The CVSS score of 7.8 indicates high severity. The EPSS score of < 1% suggests that, as of the latest data, active exploitation is unlikely, and the flaw is not listed in the CISA KEV catalog. Exploitation requires local access or an environment where the attacker can execute code on the host, such as an insider or a process with elevated privileges. Because it is a kernel‑level flaw, successful exploitation would provide unrestricted control over the affected system. Based on the description, the likely attack vector is local code execution that triggers concurrent release of multiple blk‑cgroup groups.

Generated by OpenCVE AI on July 30, 2026 at 22:19 UTC.

Remediation

No vendor fix or workaround currently provided.

OpenCVE Recommended Actions

  • Apply the kernel patch that fixes the blk‑cgroup use‑after‑free flaw (see the CVE references).
  • Reboot the system so that the updated kernel image is loaded.
  • If the host runs containers or VMs sharing the kernel, restart those workloads to ensure they use the patched kernel.

Generated by OpenCVE AI on July 30, 2026 at 22:19 UTC.

Tracking

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Advisories

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History

Tue, 21 Jul 2026 00:15:00 +0000

Type Values Removed Values Added
Weaknesses CWE-825
References
Metrics threat_severity

None

threat_severity

Moderate


Mon, 20 Jul 2026 14:45:00 +0000

Type Values Removed Values Added
Metrics cvssV3_1

{'score': 7.8, 'vector': 'CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H'}


Sun, 19 Jul 2026 12:15:00 +0000

Type Values Removed Values Added
Description In the Linux kernel, the following vulnerability has been resolved: blk-cgroup: fix UAF in __blkcg_rstat_flush() When multiple blkgs in the same blkcg are released concurrently, a use-after-free can occur. The race happens when one blkg's __blkcg_rstat_flush() removes another blkg's iostat entries via llist_del_all(). The second blkg sees an empty list and proceeds to free itself while the first is still iterating over its entries. Move the flush from __blkg_release() (RCU callback) to blkg_release() (before call_rcu). This ensures the RCU grace period waits for any concurrent flush's rcu_read_lock() section to complete before freeing.
Title blk-cgroup: fix UAF in __blkcg_rstat_flush()
First Time appeared Linux
Linux linux Kernel
CPEs cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*
Vendors & Products Linux
Linux linux Kernel
References

Subscriptions

Linux Linux Kernel
cve-icon MITRE

Status: PUBLISHED

Assigner: Linux

Published:

Updated: 2026-08-05T12:35:50.591Z

Reserved: 2026-07-19T07:54:57.013Z

Link: CVE-2026-63802

cve-icon Vulnrichment

No data.

cve-icon NVD

No data.

cve-icon Redhat

Severity : Moderate

Publid Date: 2026-07-19T00:00:00Z

Links: CVE-2026-63802 - Bugzilla

cve-icon OpenCVE Enrichment

Updated: 2026-07-30T22:30:06Z

Weaknesses
  • CWE-825

    Expired Pointer Dereference