CVE-2025-39996
Description
A use-after-free vulnerability was discovered in the Linux kernel’s b2c2 FlexCop PCI media device driver. The flaw exists in the flexcop_pci_remove() function where cancel_delayed_work() is used to cancel a pending work item (irq_check_work). Because cancel_delayed_work() does not guarantee that a running delayed work item has completed before returning, the driver may free the underlying flexcop_device structure while irq_check_work is still executing. This creates a race condition leading to a use-after-free, which can result in kernel memory being accessed after it has been freed.
Mitigation
To mitigate this issue, prevent the `flexcop-pci` kernel module from loading. Create a file named `/etc/modprobe.d/disable-flexcop-pci.conf` with the following content:
blacklist flexcop-pci
Then, regenerate the initramfs and reboot the system for the changes to take effect. For Red Hat Enterprise Linux 7 and 8, use `dracut -f`. This may impact functionality that relies on the B2C2 FlexCop PCI device. A system reboot is required for the changes to take effect.
Common Vulnerability Scoring System (CVSS) Score Details
Info alert:Important note
CVSS scores for open source components depend on vendor-specific factors (e.g. version or build chain). Therefore, Red Hat's score and impact rating can be different from NVD and other vendors. Red Hat remains the authoritative CVE Naming Authority (CNA) source for its products and services (see Red Hat classifications).
The following CVSS metrics and score provided are preliminary and subject to review.
CVSS v3 Score Breakdown
| Red Hat | NVD | cve.org | |
|---|---|---|---|
| Base Score | 4.7 | N/A | N/A |
| Attack Vector | Local | N/A | N/A |
| Attack Complexity | High | N/A | N/A |
| Privileges Required | Low | N/A | N/A |
| User Interaction | None | N/A | N/A |
| Scope | Unchanged | N/A | N/A |
| Confidentiality | None | N/A | N/A |
| Integrity Impact | None | N/A | N/A |
| Availability Impact | High | N/A | N/A |
Vector
Red Hat: CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H
Understanding the Weakness (CWE)
Integrity
Technical Impact: Modify Memory
The use of previously freed memory may corrupt valid data, if the memory area in question has been allocated and used properly elsewhere.
Availability
Technical Impact: DoS: Crash, Exit, or Restart
If chunk consolidation occurs after the use of previously freed data, the process may crash when invalid data is used as chunk information.
Confidentiality
Technical Impact: Read Memory
Read operations on freed memory can sometimes leak sensitive information instead of causing a crash
Integrity,Confidentiality,Availability
Technical Impact: Execute Unauthorized Code or Commands
If malicious data is entered before chunk consolidation can take place, it may be possible to take advantage of a write-what-where primitive to execute arbitrary code. If the newly allocated data happens to hold a class, in C++ for example, various function pointers may be scattered within the heap data. If one of these function pointers is overwritten with an address to valid shellcode, execution of arbitrary code can be achieved.
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