CVE 2025-6019: Local Privilege Escalation via udisksd and libblockdev

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CVE-2025-6019: Privilege Escalation via udisksd and libblockdev

In June 2025, a critical local privilege escalation vulnerability was disclosed in the Fedora and SUSE Linux environments involving the udisksd daemon and its backend library libblockdev. Assigned CVE-2025-6019, this vulnerability allows a user in the allow_active group to escalate privileges to root under specific conditions. This blog post walks through the vulnerability, its impact, and our detailed static and dynamic analysis, including lab simulation and patch diffing.

The vulnerability received significant attention due to its ease of exploitation in misconfigured environments and the minimal requirements needed to trigger it. It serves as a critical case study in how backend daemons and D-Bus services, when not properly sandboxed or authenticated, can become unintended vectors for full system compromise. The layered breakdown in permissions, combined with a flawed assumption of group-based trust, creates a dangerous security gap, especially on shared or multi-user systems.

Table of Contents

What is CVE-2025-6019?

CVE-2025-6019 is a local privilege escalation (LPE) vulnerability affecting systems where:

udisksd is installed and running (e.g., Fedora, SUSE)

Users in the allow_active group are trusted to execute disk-related actions

libblockdev fails to validate privileged backend operations under unprivileged contexts

When exploited, this vulnerability allows a non-root user with allow_active group membership to trigger disk mount or format actions via D-Bus calls to udisksd, leading to root code execution.

The issue stems from improper handling of the user’s authority during inter-process communications (IPC) via D-Bus. When the udisksd daemon receives a request, it incorrectly assumes that group membership is sufficient to grant permission for sensitive operations. In reality, this can be bypassed if D-Bus calls are forged or incorrectly validated, allowing for privilege elevation without proper policy enforcement.

Impact

Factor	Detail
Type	Local Privilege Escalation
Attack Vector	D-Bus communication with udisksd
Privileges Gained	root
Group Required	allow_active (or equivalent)
Affected Systems	Fedora, SUSE, systems with udisks2 + libblockdev

Static Analysis

During static review of udisks2 and libblockdev sources, we observed:

The udisksd daemon exposed several polkit-controlled methods for mounting, unlocking, and formatting devices.

In older versions, the check for group-based privilege (allow_active) was used without verifying the invoking UID context, leading to a trust boundary violation.

Backend execution through libblockdev (via D-Bus) allowed privileged operations to be queued and executed using udisksd’s elevated context.

Notable vulnerable flow:

udisks_daemon_handle_mount -> polkit_check -> blkdev_mount

This path, when abused, allowed an unprivileged user to cause udisksd to execute mount operations with root permissions. The backend layer did not perform sufficient validation or enforce granular checks, and trusted the frontend input blindly, thereby failing to prevent a privilege escalation opportunity.

Lab Setup

We replicated the environment using a Fedora 40 Docker container with systemd, udisks2, and libblockdev.

Tools Installed

udisks2, libblockdev, dbus, sudo, python3

testuser in allow_active group

Container Run:

docker run –rm -it –privileged –cgroupns=host \

-v /sys/fs/cgroup:/sys/fs/cgroup:ro \

fedora-lpe-env

We ensured:

udisksd and dbus-daemon were running

Permissions matched the target distro

This environment mimicked a real-world Fedora configuration where udisksd would typically run under systemd supervision, making the simulation highly accurate for research purposes.

Proof of Concept (PoC)

Python-Based Interactive Exploit:

import subprocess 

print("[*] Attempting to mount via udisksctl...") 

result = subprocess.run(["udisksctl", "mount", "-b", "/dev/loop0"], 

                        stdout=subprocess.PIPE, stderr=subprocess.PIPE, 

                        universal_newlines=True) 

print("STDOUT:", result.stdout) 

print("STDERR:", result.stderr) 

If the group and service are misconfigured: 

udisksctl mount -b /dev/loop0

Results in:

Mounted /dev/loop0 at /run/media/testuser/loop0

This confirmed root-controlled mounting from a non-root user. In certain edge cases, chaining this with additional udisks functions like format, unlock, or even calling into volume management can lead to full root access, especially when file-based configuration is weak or incomplete.

Patch Diffing

By comparing patched and vulnerable versions of udisks2:

Vulnerable:

if (caller_in_allow_active_group()) { 

    return ALLOW_MOUNT; 

} 

Patched: 

if (caller_in_allow_active_group() && caller_uid == 0) { 

    return ALLOW_MOUNT; 

}

Additionally, Fedora updated Polkit rules:

/org/freedesktop/UDisks2/Manager:

-> now enforces stricter UID-based checks.

The patch introduced a stricter verification path that eliminates the group-only trust model and shifts entirely to polkitd + uid-based policy enforcement. In some cases, udisks2 builds were also recompiled to disable unsafe legacy options that allowed D-Bus triggers without secure context tokens.

Conclusion

CVE-2025-6019 highlights the dangers of implicit trust in system-level groups like allow_active. When backend daemons like udisksd execute user-requested operations with elevated privileges, improper boundary checks can easily lead to full system compromise. Users should immediately update udisks2 and libblockdev, audit group-based permissions, and apply stricter polkit rules.

This case also underscores the importance of threat modeling system services that interact with IPC buses and handle hardware. Even if upstream tools implement group-based safety, failing to account for privilege transitions or assuming benign frontend inputs can render such designs insecure.

For expert guidance on vulnerability management and/or penetration testing services contact SecureLayer7 to leverage tailored solutions and stay ahead of evolving security risks.

References