CVE-2021-25395

What it actually does

This vulnerability is a local, high-complexity race condition in the Samsung MFC charger driver used on affected Android/Samsung mobile devices prior to the May 2021 Security Maintenance Release. If an attacker has already compromised a highly privileged radio/baseband-related context, they can exploit a timing flaw to bypass a signature check. Successful exploitation can undermine code or firmware validation boundaries and may allow the attacker to affect confidentiality, integrity, and availability on the device.

Why it matters to the business

The primary risk is post-compromise escalation on affected mobile devices: an attacker who already has deep device access may be able to bypass trusted validation controls and gain broader control over the handset. Because this issue is listed in the CISA Known Exploited Vulnerabilities catalog and has confirmed exploitation in the wild, organizations that allow affected Android/Samsung devices to access enterprise email, messaging, VPN, or mobile apps should treat remediation as a priority even though exploitation requires high privileges and local access. The CISA remediation deadline was 2023-07-20, so any still-unpatched devices represent overdue exposure.

How an attack unfolds

An attacker first needs a foothold with radio-level or similarly privileged access on an affected Android/Samsung device. From that position, they interact with the vulnerable MFC charger driver and attempt to win a race condition around the signature-check workflow. By carefully timing operations, the attacker can cause the driver to accept or proceed with content that should have failed validation. Because the vulnerability sits below normal application privilege boundaries, successful exploitation may help a device-level attacker bypass a trusted enforcement point, persist deeper on the device, alter protected components, or chain with other mobile exploits. Public metadata indicates this vulnerability has been exploited in the wild, but no ransomware use is reported.

How to fix it

Apply the vendor security update that includes Samsung SMR MAY-2021 Release 1 or a later security maintenance release for affected Samsung/Android devices. Where exact package fixed versions are unavailable, use the Android security patch level and OEM firmware build as the authoritative remediation source. Devices that cannot receive the May 2021 or later Samsung security update should be retired, isolated from enterprise resources, or restricted through mobile device management controls. Enforce MDM compliance policies requiring current Android security patch levels, block rooted or tampered devices, and limit access from unmanaged or unsupported mobile devices. Because this is a local post-compromise issue, network-only mitigations are not sufficient.

How to confirm the fix worked

Confirm each managed device reports an Android security patch level and OEM firmware/security maintenance release that includes Samsung SMR MAY-2021 Release 1 or later. Validate through MDM inventory, device compliance reports, OEM build fingerprints, and Android security patch metadata rather than application version alone. Spot-check representative devices manually under Settings > About phone > Software information, confirming the security patch level is May 2021 or newer for affected Samsung models. Devices that remain on pre-May 2021 security releases should be treated as vulnerable unless the OEM has documented a backported fix. Also verify that enterprise access controls deny noncompliant, rooted, bootloader-unlocked, or unsupported devices.

Typical attack path

1. Identify an affected Android/Samsung mobile device running firmware prior to the May 2021 security update.
2. Obtain local high-privilege execution, such as compromise of a radio/baseband-related privileged context.
3. Trigger interactions with the MFC charger driver involved in signature validation.
4. Repeatedly manipulate timing to win the race condition during the signature-check sequence.
5. Bypass the intended signature check and cause the device to accept or process unauthorized content.
6. Use the bypass to expand device control, tamper with protected components, or support a broader mobile compromise chain.

How to detect it

Detection is difficult because exploitation occurs locally at a low device-driver level and may not produce clear application-layer logs. Review MDM/UEM inventory for devices running pre-May 2021 Samsung security releases, rooted or bootloader-unlocked states, failed device integrity checks, unexpected firmware/build changes, or repeated compliance state changes. Collect Android logcat, kernel logs, tombstones, and mobile threat defense telemetry where available, focusing on anomalous activity involving charger, MFC, radio/baseband, firmware validation, SELinux denials, kernel crashes, or privileged service restarts. Look for signs of chained compromise: unknown privileged binaries, modified system partitions, unexpected persistence mechanisms, abnormal baseband/radio behavior, repeated kernel panic/reboot events, or security policy disablement. If threat-hunting historical exploitation, correlate device patch level at the time of suspicious activity with any MTD alerts, unexplained crashes, baseband anomalies, or integrity failures.

• Android security patch level before 2021-05-01 on affected Samsung devices
• Samsung SMR before MAY-2021 Release 1
• ro.boot.verifiedbootstate=orange
• ro.boot.verifiedbootstate=red
• ro.boot.flash.locked=0
• /system/xbin/su
• /system/bin/su
• /sbin/su
• /system/app/Superuser.apk
• /system/priv-app/Superuser.apk
• /data/adb/magisk
• /sbin/.magisk
• avc: denied
• charger
• mfc
• radio
• baseband
• tombstone
• kernel panic
• dm-verity verification failed

What your security team should do

• Prioritize identification and remediation of affected Samsung/Android devices because the vulnerability is in the CISA Known Exploited Vulnerabilities catalog and exploitation has been observed in the wild.
• Use MDM or UEM tooling to require Samsung SMR MAY-2021 Release 1 or later, or an equivalent Android/OEM security patch level that includes the fix.
• Block or quarantine devices that cannot be updated, are rooted, have unlocked bootloaders, or fail device integrity checks.
• Review mobile threat defense telemetry for signs of baseband/radio compromise, abnormal privileged service behavior, or unexpected charger-driver/kernel interactions.
• Ensure mobile incident response procedures include collection of device logs, firmware/build information, MDM compliance history, and indicators of rooting or persistence.
• For high-risk users, consider enhanced mobile threat defense monitoring and rapid replacement of legacy devices that no longer receive OEM security updates.