CVE-2026-21131

Executive Summary

CVE-2026-21131 is an incorrect default permission vulnerability in Samsung Flow prior to version 4.9.22.4. A local attacker on the connected device can leverage the flawed permission configuration to launch an arbitrary activity under the privileges of the Samsung Flow application. Successful exploitation may allow unauthorized access to protected functionality, data exfiltration, or lateral movement within the Samsung Flow trust boundary, depending on what permissions the application holds.

Technical Analysis

The vulnerability resides in Samsung Flow, a cross-device continuity and screen-sharing application that links Samsung mobile devices with Windows PCs and tablets. According to the NVD description, the root cause is an "incorrect default permission" that allows a local attacker to "launch an arbitrary activity with Samsung Flow privileges on the connected device."

Samsung Flow comprises multiple components, including a Windows-side service/application and an Android-side companion app. The flawed default permission likely applies to an exported Activity or inter-process communication (IPC) endpoint exposed by one of these components. Because the permission is configured incorrectly by default, an attacker who can execute code locally on the same device (or a device within the Samsung Flow trust relationship) can send an Intent to launch an Activity belonging to Samsung Flow without being restricted by normal permission checks.

The impact of launching an arbitrary activity with Samsung Flow privileges depends on what that activity can do. Activities running in Samsung Flow's process inherit the application's granted permissions. If Samsung Flow holds permissions for screen capture, file access, notification access, or Bluetooth/Wi-Fi peer discovery, the attacker may be able to invoke functionality that should require user interaction or explicit authorization. This is a classic "confused deputy" or permission re-delegation issue where the vulnerable app acts as the deputy executing actions on behalf of a lower-privileged caller.

Specific exported component names, intent action strings, permission declarations in the manifest, or API parameters are not provided in the NVD description and cannot be determined from the available data. The CVSS vector CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H reflects a local attack vector, low complexity, no privileges required, no user interaction, with scope change (S:C), and high confidentiality, integrity, and availability impacts. The scope change indicates that the vulnerable component impacts resources beyond its security scope — consistent with an attacker leveraging Samsung Flow's privileges to affect the connected device or broader system resources.

The "connected device" phrase in the description suggests the exploit requires an established Samsung Flow connection between two devices (e.g., a phone and a PC). The local attacker must already have code execution or an untrusted app installed on one side of that connection to send the malicious intent or IPC message.

Exploitation Scenarios

No public PoC or exploit code is available for CVE-2026-21131. The following attack chain is inferred from the vulnerability class (incorrect default permission / permission re-delegation) and the NVD description. No specific function names, class names, URL endpoints, or parameter names are invented; only the concepts present in the description are used.

1) Reconnaissance / Target Identification The attacker must first identify a target device that is running Samsung Flow prior to version 4.9.22.4 and that is currently connected (paired) with another device. On Android, the attacker would enumerate installed packages and exported components using standard tooling (e.g., pm list packages, manifest analysis via available local utilities) to identify Samsung Flow components that are accessible without requiring a signature-level or dangerous permission. On Windows, the attacker would identify the Samsung Flow application and its registered URI handlers, COM objects, or IPC endpoints. The key reconnaissance objective is to find an exported Activity (or equivalent IPC entry point) that is improperly protected by default.

2) Triggering the Flaw The attacker, having local code execution on the device (e.g., a malicious app with minimal permissions, or a process running under a low-privileged account), constructs an Intent (or IPC message) that targets the improperly exported Activity within Samsung Flow. Because the default permission is configured incorrectly, the caller is not required to hold a specific permission to invoke the component. The Intent is delivered to Samsung Flow's process, and the Activity is launched.

3) Payload / Execution Method (vulnerability-class level) The launched Activity executes within Samsung Flow's process, inheriting Samsung Flow's privileges. Depending on the Activity's function, the attacker may be able to invoke a privileged operation — such as reading or writing files accessible to Samsung Flow, interacting with the connected device, accessing account tokens, or triggering UI flows that perform sensitive actions on the user's behalf. This is a permission re-delegation attack: the attacker's low-privilege context causes a high-privilege component to perform an action. No specific payload format can be described without the actual exported component details, which are not available.

4) Post-Exploitation Impact Successful exploitation can lead to confidentiality, integrity, and availability impacts rated HIGH by the CVSS vector. The attacker could potentially exfiltrate data accessible to Samsung Flow, modify data or settings within the Samsung Flow trust boundary, or disrupt the service. Because the scope is changed (S:C), the compromise could extend beyond Samsung Flow itself to the connected device or shared resources. If the launched activity supports screen sharing or file transfer, the attacker might gain unauthorized visibility into the connected device's screen or files, or inject content.

No evidence of exploit-in-the-wild or threat actor campaigns targeting this specific CVE is available at the time of writing.

Impact Assessment

The CVSS v3.1 vector CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H yields a base score of 9.3 (Critical), assuming the vector is accurate. This is derived from:

• AV:L (Local): The attacker requires local access to the target device. This is a significant barrier; remote unauthenticated exploitation is not possible.
• AC:L (Low): No special conditions or race conditions are required; the attack is straightforward once local access is obtained.
• PR:N (None): The attacker does not need any prior authorization or privileges on the target device beyond the ability to send the malicious intent/IPC message.
• UI:N (None): No user interaction is required; the activity launches without the victim's knowledge or consent.
• S:C (Changed): The impact extends beyond the vulnerable component (Samsung Flow) to other resources within the trust boundary, such as the connected device.
• C:H / I:H / A:H: High confidentiality, integrity, and availability impacts, indicating potential full compromise of data and functionality accessible to Samsung Flow.

Business Impact Samsung Flow is used in enterprise and personal contexts to connect mobile devices to PCs for screen mirroring, file sharing, and notification sync. A local attacker on a connected device could exploit this to:

• Access corporate data synchronized through Samsung Flow (e.g., notifications containing email/Slack messages, shared files).
• Perform actions on the connected PC as the Samsung Flow user, potentially leading to lateral movement within a corporate network.
• Exfiltrate sensitive information displayed on the connected device.
• Disrupt business continuity by interfering with screen-sharing or file-transfer operations.

Affected Systems All installations of Samsung Flow on Android and Windows prior to version 4.9.22.4 are potentially affected. The blast radius is limited to devices that have an active Samsung Flow connection. Enterprise environments that permit personal device connectivity to corporate PCs via Samsung Flow are at higher risk.

Detection Guidance

Sigma Rule

title: Suspicious Activity Launch via Samsung Flow Default Permission Abuse
id: a1b2c3d4-5678-90ab-cdef-1234567890ab
status: experimental
description: Detects potential exploitation of CVE-2026-21131 where a local attacker launches an arbitrary activity with Samsung Flow privileges.
references:
  - https://nvd.nist.gov/vuln/detail/CVE-2026-21131
author: Threat Intelligence Team
date: 2026-01-01
tags:
  - attack.t1626
  - cve.2026-21131
logsource:
  product: android
  service: activity_manager
detection:
  selection:
    EventType: 'am_activity_launch'
    PackageName: 'com.samsung.android.sflow'
    CallerPackageName|not: 'com.samsung.android.sflow'
  condition: selection
falsepositives:
  - Legitimate Samsung Flow internal activity launches
  - Debugging or development activities
level: high

YARA Rule

rule CVE_2026_21131_SamsungFlow_Permission_Abuse
{
    meta:
        description = "Detects potential exploitation indicators for CVE-2026-21131 in Samsung Flow components"
        author = "Threat Intelligence Team"
        date = "2026-01-01"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2026-21131"
        severity = "high"

    strings:
        $pkg1 = "com.samsung.android.sflow" ascii wide nocase
        $pkg2 = "Samsung Flow" ascii wide nocase
        $ver = "4.9.22.4" ascii wide
        $perm1 = "android.permission." ascii wide
        $intent = "android.intent.action." ascii wide

    condition:
        uint16(0) == 0x4D5A or uint32(0) == 0x504B0304 or uint32(0) == 0x03000800
        and 2 of ($pkg*) and 1 of ($ver, $perm1, $intent)
}

Suricata IDS Rule

alert tcp any any -> any any (msg:"CVE-2026-21131 Samsung Flow Default Permission Abuse - Suspicious IPC/Intent"; flow:to_server,established; content:"com.samsung.android.sflow"; nocase; content:"android.intent.action"; nocase; content:"4.9.22"; nocase; threshold:type limit, track by_src, count 1, seconds 60; classtype:attempted-user; sid:202621131; rev:1; reference:cve,2026-21131;)

Elastic Detection

sequence by host.id with maxspan=5s
  [process where process.name == "am" and process.args : "*com.samsung.android.sflow*" and not process.parent.name : "com.samsung.android.sflow"]
  [process where process.name : ("sh", "su") and process.args : ("*intent*", "*startactivity*")]

Splunk SPL Query

index=android OR index=endpoint
(sourcetype="android:logcat" OR sourcetype="WinEventLog:Application")
("com.samsung.android.sflow" OR "Samsung Flow")
AND ("am_activity_launch" OR "ActivityManager" OR "intent.action")
| search NOT process_name="com.samsung.android.sflow"
| stats count min(_time) as first_seen max(_time) as last_seen values(dest) as affected_hosts by src_user process_name
| where count > 0
| sort - count
| convert ctime(first_seen) ctime(last_seen)

Wazuh OSSEC Rule

<group name="samsung_flow,cve_2026_21131,">
  <rule id="202621131" level="12">
    <decoded_as>json</decoded_as>
    <field name="package">com.samsung.android.sflow</field>
    <field name="event">activity_launch</field>
    <field name="caller_package" negate="yes">com.samsung.android.sflow</field>
    <description>CVE-2026-21131: Potential Samsung Flow default permission abuse - activity launched by external package</description>
    <mitre>
      <id>T1626</id>
    </mitre>
    <group>cve_2026_21131,</group>
  </rule>
</group>

Mitigation & Patch Guidance

Patch confidence: 0/4 (UNPATCHED — no patch evidence from any tracked source).

1) Immediate Mitigations

• If Samsung Flow is not required, uninstall or disable it on both the mobile and PC sides to remove the attack surface.
• Restrict local code execution on devices that run Samsung Flow: enforce application whitelisting, disable developer options, and block installation of untrusted APKs or executables.
• Disconnect Samsung Flow pairings when not actively needed to reduce the window of opportunity; an active connection appears to be a precondition.
• On Android, audit exported components of Samsung Flow and, where device management allows, use enterprise mobility management (EMM) to restrict inter-app communication or block the app entirely.
• On Windows, apply the principle of least privilege to user accounts and monitor for suspicious child processes launched from the Samsung Flow application.

2) Patch / Upgrade Steps

• Upgrade Samsung Flow to version 4.9.22.4 or later on all affected devices. The NVD description states the vulnerability applies "prior to version 4.9.22.4," implying 4.9.22.4 is the fixed version.
• No vendor advisory or patch source was tracked at the time of writing (Patch Sources: []). Verify availability through Samsung's official channels (Samsung Flow app store listing, Samsung Mobile Security updates) before deployment.
• Because no patch evidence exists from tracked sources, treat the fix as unconfirmed and validate the version string on the device after upgrading.

3) Long-Term Hardening

• Adopt a mobile threat defense (MTD) solution that detects permission re-delegation and intent-based abuse.
• Enforce a policy of minimum necessary permissions for cross-device continuity apps in the enterprise.
• Regularly review the exported components and default permission configurations of all pre-installed and enterprise-approved applications as part of secure configuration baselines (CIS Benchmarks for Android and Windows).
• Monitor Samsung security bulletins and NVD for updates to this CVE; re-evaluate patch confidence when a vendor fix is published.
• Consider network segmentation to limit the blast radius if a connected PC is compromised via Samsung Flow.

References

1. NVD — CVE-2026-21131: https://nvd.nist.gov/vuln/detail/CVE-2026-21131
2. Samsung Mobile Security Updates: https://security.samsungmobile.com/
3. Samsung Flow on Galaxy Store / Microsoft Store (official distribution channels for version verification)
4. CWE-276: Incorrect Default Permissions — https://cwe.mitre.org/data/definitions/276.html
5. MITRE ATT&CK T1626 — Abuse Elevation Control Mechanism: https://attack.mitre.org/techniques/T1626/

No known threat actor campaigns or exploit-in-the-wild evidence are associated with CVE-2026-21131 at the time of writing. EPSS score has not yet been assigned by FIRST.org. CISA KEV status: NO.