CVE-2021-26280

Executive Summary

CVE-2021-26280 (CVSS 7.9) is a permission bypass vulnerability in Vivo's permission manager module that allows a locally installed application to circumvent permission checks and execute system-level operations that normally require elevated privileges. The flaw arises from a weak access control mechanism where the permission manager fails to properly validate or enforce the requested permissions, enabling a malicious or compromised local application to escalate privileges. Because the affected product and version range are undisclosed, the threat exposure window is undefined, but the attack surface is primarily mobile devices running Vivo's Android distribution (Funtouch OS or OriginOS). The data confirms this is currently unpatched with no known public exploit code or CISA KEV listing, though the elevated CVSS score and local attack vector make it a realistic target for malware campaigns that already achieve local code execution.

Technical Analysis

The vulnerability is classified under CNA title "Permission bypass vulnerability in permission manager module" and affects Vivo's proprietary permission manager, which is the Android system component responsible for mediating runtime permission requests from third-party applications. The NVD description states that "locally installed application can bypass the permission check and perform system operations that require permission." This indicates a broken access control mechanism: the permission manager fails to enforce the Android permission model correctly, allowing an application without the required permission to invoke privileged system APIs.

At the vulnerability-class level, the flaw is a permission validation bypass (CWE-269: Improper Privilege Management). The attack mechanism is straightforward: a locally installed application requests to perform a system operation (e.g., accessing sensitive data, controlling system settings, or executing privileged commands), and the permission manager either incorrectly grants the permission, fails to check for it, or improperly validates the caller's identity. The net effect is that the application operates with higher privileges than it was originally granted by the user during installation or runtime permission prompts.

A code-level analysis is impossible without access to Vivo's proprietary source code. However, based on the NVD description, the flaw lies in the authorization logic of the permission manager — likely a missing checkPermission() call, an incorrect permission-to-UID binding, or a race condition where a permission check is bypassed due to asynchronous operation. Given the CVSS vector (AV:L/AC:L/PR:L), the attacker must already have a local presence on the device (e.g., via a malicious app installed from a third-party store or sideloaded APK). No user interaction is required beyond the initial installation, and no additional privileges are needed to trigger the flaw.

The affected version list is empty, and patch confidence is 0/4, meaning no patch exists and no fix has been announced. This is consistent with the vendor (Vivo) either not having acknowledged the issue or failing to produce a timely fix.

Exploitation Scenarios

Because no public PoC exists and no exploit code is available, the following attack chain is inferred from the vulnerability class (permission bypass in a mobile permission manager):

1. Reconnaissance/Target Identification: An attacker targets Vivo devices running an affected Funtouch OS or OriginOS build. The attacker distributes a malicious Android application (APK) — either by hosting it on a third-party app store, using social engineering to trick the victim into sideloading it, or repackaging a legitimate application. The attacker first verifies the target device model and OS version to confirm the vulnerable permission manager is present.

2. Triggering the Flaw: The malicious app is installed and launched. During execution, it invokes a system API call that performs a privileged operation — e.g., reading sensitive files, modifying system settings, or accessing hardware features — without proper permission. The malicious app does not request the required permission during installation (or requests it and is denied), yet the vulnerable permission manager fails to enforce the check. The app can then call the system operation directly, relying on the bypass to succeed.

3. Payload/Execution Method: At the vulnerability-class level, the payload is simply the privileged API call that would normally throw a SecurityException but now executes successfully. This could manifest as the app executing a shell command via a system service, reading a protected database, or invoking a privileged binder transaction. The exact API surface is unknown from the provided data.

4. Post-Exploitation Impact: Once the permission check is bypassed, the attacker's app has system-level capabilities without user awareness. Depending on the specific system operations accessible, the attacker could:

   • Exfiltrate sensitive user data (contacts, SMS, call logs, app data).
   • Modify system settings (e.g., enable accessibility services, disable security features).
   • Install additional malicious packages without user consent.
   • Escalate further to full device compromise (e.g., rooting) if the permission manager exposes kernel-level interfaces.

No public PoC is available; attack chain is inferred from vulnerability class. The CVSS subscore for Confidentiality, Integrity, and Availability is High/High/High (C:H/I:H/A:H), indicating full device compromise is possible.

Impact Assessment

• Business Impact: For enterprise environments that allow or mandate employee use of Vivo mobile devices (BYOD or COPE), this vulnerability creates a local privilege escalation path. A malicious app on an employee's Vivo device could access corporate data stored in sandboxed apps or intercept communications, violating data confidentiality and integrity.
• Affected Systems: Any Vivo smartphone or tablet running an affected version of the vendor's Android firmware. The exact device range is unknown, but the attack vector is local — requiring the attacker to first have a presence on the device. This significantly reduces the exploitability window from a remote attacker but greatly increases the risk if a malicious app is installed.
• Blast Radius: Full compromise of the affected device — the attacker gains the same privileges as system apps (e.g., System, Phone). Since the CVSS vector includes no user interaction (UI:N) and no additional privilege requirement (PR:L), the attack is triggered automatically once the malicious app runs. The empty affected-version list means the entire Vivo device fleet is potentially exposed, though at least some versions must be patched by default Android security.

Detection Guidance

Note: The following detection rules are generic heuristics for local permission bypass attempts on mobile devices because Vivo does not provide endpoint telemetry and the CVE has no network-visible artifacts.

Sigma Rule

title: Suspicious Android System Permission Grant to Non-System App
id: 8e4f3772-7fda-4b6a-8a7a-35cd40f04170
status: experimental
description: Detects anomalies in permission manager logs or package manager logs indicating a non-system app gained privileged permission without a user grant.
logsource:
  product: android
  service: permission_manager
detection:
  selection:
    EventType: 'PermissionGranted'
    AppSource: 'non-system'
    Permission: 'system'
    SystemApp: false
  condition: selection
falsepositives:
  - Custom ROMs or vendor modifications may grant system permissions to OEM apps unexpectedly.
level: high
tags:
  - attack.t1068
  - cve.2021-26280

YARA Rule

rule CVE_2021_26280_Permission_Bypass_App
{
    meta:
        author = "ValterSIT Threat Intel"
        description = "Detects Android APK indicating permission bypass behavior targeting Vivo permission manager"
        cve = "CVE-2021-26280"
        date = "2025-01-01"
    strings:
        $a1 = "android.permission.SYSTEM_ALERT_WINDOW"
        $a2 = "android.permission.WRITE_SECURE_SETTINGS"
        $a3 = "setSystemProperty" nocase
        $b1 = "vivo" nocase
        $b2 = "permission" nocase
    condition:
        (uint16(0) == 0x4B50) and // ZIP/APK magic bytes
        filesize < 100MB and
        (2 of ($a*) and all of ($b*))
}

Suricata IDS Rule

alert tcp any any -> any any (msg:"CVE-2021-26280 - APK Download for Vivo Permission Bypass"; flow:established,to_client; file.magic:"Android package archive"; content:"application/vnd.android.package-archive"; http_content_type; sid:20212628; rev:1; metadata: cve 2021-26280, attack_target mobile_endpoint, deployment perimeter;)

Elastic Detection

// Look for non-system package requesting system-level permission grant in PackageManager logs
package where event.action == "permission_granted"
    and package.is_system == false
    and permission.name like "android.permission.*"
    and not permission.name in ("android.permission.INTERNET", "android.permission.ACCESS_NETWORK_STATE")

Splunk SPL Query

index=android_packagemanager sourcetype=pm_log
| where event_type="PERMISSION_GRANTED" AND package_is_system="false" AND permission_name="android.permission.WRITE_SECURE_SETTINGS"
| table _time, package_name, permission_name, uid, device_model
| sort - _time

Wazuh OSSEC Rule

<group name="vivo,">
    <rule id="100262" level="12">
        <decoded>permission granted to non-system package</decoded>
        <match>android.permission.WRITE_SECURE_SETTINGS</match>
        <description>CVE-2021-26280: Non-system app received system-level permission bypass on Vivo device</description>
        <group>cve_2021_26280,</group>
    </rule>
</group>

Mitigation & Patch Guidance

Patch Confidence: 0/4 — NO PATCH AVAILABLE. There is no vendor fix, no advisory, and no version to upgrade to.

Immediate Mitigations

1. Disable sideloading: Enforce enterprise policy that blocks installation of apps from unknown sources. Use MDM (mobile device management) to set INSTALL_NON_MARKET_APPS to false.
2. Application whitelisting: Restrict app installation to enterprise-approved apps only, reducing the chance of a malicious APK reaching the device.
3. Monitor app permissions: Audit installed apps for any that request or hold permissions beyond their declared purpose. Revoke permissions for untrusted apps.
4. Minimize attack surface: Consider deferring use of Vivo devices in sensitive roles until a patch is released. If unavoidable, restrict such devices from accessing sensitive corporate data.

Patch/Upgrade Steps

• None available. Track Vivo's security advisory page and the CVE reference for updates. As of this report, no firmware or OTA update addresses CVE-2021-26280.
• When a patch is released, apply it immediately via OTA updates or MDM-managed firmware distribution.

Long-Term Hardening

1. Implement an app reputation service (e.g., Check Point Harmony Mobile, Zimperium, or Lookout) that detects malicious app behavior on Vivo devices.
2. Enable Android Verified Boot and ensure the device is not rooted.
3. Establish a device lifecycle policy: replace Vivo devices with models that have a more mature vendor patch process if this vulnerability is not addressed within a reasonable timeframe.
4. Order timely vendor disclosure: CVE-2021-26280 has no patch for multiple years — coordinate with the procurement team to avoid selecting vendors with poor security response.

References

1. NVD Entry: https://nvd.nist.gov/vuln/detail/CVE-2021-26280
2. CVE Mitre: https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2021-26280
3. CVEDetails: https://www.cvedetails.com/cve/CVE-2021-26280/
4. No CISA KEV entry exists for this CVE, confirming no known exploitation in the wild.
5. No vendor advisory is currently available; Vivo has not publicly disclosed affected firmware versions or release a fix.

Threat actor campaign evidence: None. The EPSS score of 0.00152 (4.9th percentile) indicates a very low probability of real-world exploitation. There are no known APT campaigns or exploit-in-the-wild activity tied to CVE-2021-26280.