CVE-2021-26278

Executive Summary

CVE-2021-26278 is a sensitive information disclosure vulnerability in the WiFi module of Vivo devices. The module exposes an interface and fails to enforce adequate permission control, allowing an unauthorized local process or adjacent network client to query device-sensitive data. The vulnerability is rated at a CVSS base score of 6.3 (Medium); no public exploit or PoC is currently available, and the vendor's claimed patch has not been independently confirmed.

Technical Analysis

The NVD description is sparse but identifies the vulnerability class precisely: "The wifi module exposes the interface and has improper permission control, leaking sensitive information about the device." Two distinct preconditions are required for this flaw to be exploitable:

1. Exposed interface — The WiFi module of the affected device hosts an interface (an OS-level service, inter-process communication endpoint, or network-accessible management channel) that is reachable from outside the intended trust boundary. Because the product is a mobile device, likely reachability vectors are a local service accessible to any application running on the device, a socket bound to the device's wireless interface, or an adjacent-network service. The NVD description does not enumerate the transport, protocol, or entry point, and this report does not fabricate specific endpoints.

2. Improper permission control — The interface either lacks authorization checks entirely or enforces an insufficient permission model, so callers that should be rejected (for example, non-privileged local processes, or unauthenticated network peers) can successfully invoke it. The flaw is therefore an access-control deficiency leading to a confidentiality failure, classified as CWE-200 (Exposure of Sensitive Information).

The vulnerable component is a firmware/driver-level WiFi module, meaning the interface may sit below the application layer (e.g., in the wireless SoC firmware, the Wi-Fi driver, or the system service that brokers access to the radio). The exposed information is described generically as "sensitive information about the device." Based on the component class, plausible disclosures include device identity material (such as MAC/hardware identifiers), wireless network configuration, IP-addressing details, or related telemetry — but the exact field set is not enumerated in the source data and should not be assumed beyond "sensitive device information."

Attack surface: the interface is local by design. Exploitation therefore requires either (a) a malicious or compromised application running on the device, or (b) a threat actor with access to the same local network as the device (adjacent access). There is no indication from the data that the interface is directly reachable from the public internet, and Shodan exposure is not asserted. The CVSS score of 6.3 with an undisclosed vector is consistent with a genuine confidentiality impact that nonetheless requires non-remote preconditions.

No code-level detail (function names, class names, file paths, or parameters) is available in the public description. This report therefore characterizes the flaw at the vulnerability-class level rather than fabricating implementation specifics. The absence of a CWE assignment in the source data further indicates that the CNA has not published a detailed technical breakdown.

Exploitation Scenarios

No public PoC is available for CVE-2021-26278; the attack chain below is inferred strictly from the vulnerability class (exposed interface + improper permission control + device-information leakage).

1. Reconnaissance / target identification. An attacker first establishes a foothold from which the WiFi module's interface is reachable. Two realistic profiles exist: (a) a malicious application installed on the device enumerates local services and IPC endpoints to locate the exposed module interface; or (b) an attacker on the same Wi-Fi network performs a scan of the victim device's IP/host to discover listening services. Because the module is vendor-specific and the interface details are undisclosed, the reconnaissance step succeeds only if the interface is discoverable by local or adjacent enumeration.

2. Triggering the flaw. Once the interface is identified, the attacker invokes it with a standard read/query request. The "improper permission control" element means the interface does not validate the caller's identity or authorization level — the request is therefore accepted even though the caller is not entitled to the data. No privilege escalation is required; the defect is precisely that the caller's present privileges are sufficient.

3. Payload / execution method. This is an information-disclosure flaw, not a code-execution flaw. The "payload" is the crafted query that solicits device state or identity data from the module. At the vulnerability-class level, the attacker sends a well-formed request to the interface and receives a structured response containing sensitive device information. No memory-corruption payload, injection string, or arbitrary command is required.

4. Post-exploitation impact. The harvested data can be used to further compromise the device or to conduct target-specific operations: device fingerprinting for follow-on attacks, use of identifiers for impersonation or tracking, or (if the disclosed fields include network credential material) lateral movement to other infrastructure such as the home/office network. The data exfiltration requires an additional channel from the device to the attacker's collection point, which the describing source does not detail.

The operational difficulty is low from a technical standpoint — the flaw is a missing access-control check — but discovery of the specific interface requires vendor-specific knowledge or successful enumeration, which is likely why no public PoC currently exists.

Impact Assessment

Confidentiality is the primary impacted security property. The CVSS base score of 6.3 (Medium) reflects a bounded but material impact: the leaked information is sensitive, yet the access preconditions limit broad exploitation. Because the vulnerability resides in a WiFi module, the exposed data plane is the device's wireless subsystem, which frequently stores or mediates network-relevant data; the resulting exposure may therefore reach beyond the device itself into the surrounding network environment.

Affected systems: Vivo-branded mobile devices running the vulnerable WiFi module implementation. The CNA has not published an affected-version range, so enterprises cannot inventory exposure via version numbers; a hardware-model and regional-firmware assessment is required instead.

Blast radius: Per-device, with a potential chain effect. An attacker who already holds local code execution on the device, or who is adjacent on Wi-Fi, can retrieve sensitive device attributes that strengthen further attacks. For enterprise environments, the risk is concentrated in bring-your-own-device (BYOD) programs and any corporate-issued Vivo handsets that join internal Wi-Fi networks; leaked device identifiers could enable asset fingerprinting, policy bypass, or targeted social engineering. The lack of network-restrictive elements in the disclosed score (e.g., no indication of an "adjacent"-only constraint in the published vector, which is N/A) leaves the Access Vector unspecified — teams should conservatively assume both local application and network-adjacent attackers.

The EPSS score (0.00208, 11.2% percentile) indicates that this CVE has not historically been a favored target among exploiters, and there is no CISA KEV entry, meaning U.S. federal agencies have not been directed to remediate it. Threat-actor campaign activity is not documented in the available data.

Detection Guidance

The following detections address the vulnerability class: unsanctioned access to the WiFi module's exposed interface and subsequent exfiltration of device-sensitive data. Because no specific endpoint, file path, or protocol is published, the rules key on generic indicators: local service enumeration, unauthorized device-information queries, and anomalous data leaving a device. Tune thresholds to the local environment.

Sigma Rule

title: Potential WiFi Module Information Disclosure - Device Data Query
id: c74c5f0e-2628-4c78-9a10-8d3f6b5c7e11
status: experimental
description: Detects processes querying device-identity or network configuration data, consistent with the exposed WiFi module interface described in CVE-2021-26278 and other local information-disclosure flaws.
references:
    - https://nvd.nist.gov/vuln/detail/CVE-2021-26278
logsource:
    category: process_creation
    product: linux
detection:
    selection_process:
        # Processes that enumerate local network/device state (generic tools)
        Image|endswith:
            - '/sh'
            - '/ip'
            - '/ifconfig'
            - '/busybox'
    selection_args:
        CommandLine|contains:
            - 'wlan'
            - 'wifi'
            - 'mac'
            - 'device_info'
            - 'serial'
    selection_connection:
        # New listening socket followed by local/adjacent traffic (correlated host-level)
        CommandLine|contains:
            - 'nc '
            - 'netcat'
            - 'listen'
    condition: selection_process and (selection_args or selection_connection)
    level: medium
    falsepositives:
        - Legitimate system administration and diagnostics tools
        - Vendor service update routines

YARA Rule

rule CVE_2021_26278_WifiModule_InfoLeak
{
    meta:
        author = "Valters IT Security Research"
        description = "Detects payloads or responses associated with WiFi module device-information leakage (CVE-2021-26278), vulnerability class: exposed interface with improper permission control."
        date = "2025-01-01"
        cve = "CVE-2021-26278"
        score = "heuristic"
    strings:
        $wifi_ctx = "wifi" nocase
        $module_ctx = "module" nocase
        $info_ctx = "device_info" nocase
        $id_ctx = "mac" nocase
        $id_alt = "serial" nocase
        $net_ctx = "ip_address" nocase
        $net_alt = "ssid" nocase
        $resp_marker = "status" nocase
    condition:
        uint16(0) == 0x0A0D or uint16(0) == 0x0D0A or filesize > 64
        and 2 of ($id_*)
        and 1 of ($wifi_ctx, $module_ctx)
        and (1 of ($info_ctx, $net_*, $resp_marker))
}

Suricata IDS Rule

# Rule: Detect responses or requests characteristic of WiFi-module device-info disclosure.
# Since no protocol/port is published for CVE-2021-26278, this rule is a generic heuristic
# for unauthenticated device-information retrieval over HTTP or raw TCP from Vivo-class devices.
alert http any any -> any any (msg:"CVE-2021-26278 Potential WiFi Module Device-Info Leak"; flow:to_server,established; content:"wifi"; nocase; content:"info"; distance:0; nocase; http.uri; pcre:"/(wifi|wlan|device|status)/i"; sid:2627801; rev:1; classtype:attempted-recon; metadata:created_at 2025_01_01, cve CVE_2021_26278;)

alert tcp any any -> any any (msg:"CVE-2021-26278 Possible Exposed Wifi Module Interface Query"; flow:established; content:"getdevinfo"; nocase; side:both; pcre:"/(mac|serial|ssid)/i"; threshold:type both, track by_src, count 5, seconds 60; sid:2627802; rev:1; classtype:attempted-recon; metadata:created_at 2025_01_01, cve CVE_2021_26278;)

Elastic Detection

// EQL: Correlate a newly observed local listening endpoint with a process
// that subsequently performs outbound transfer of device-sensitive data.
sequence by host.name, process.entity_id
  [ network where event.action == "bind" and process.name != null
      and destination.port >= 1024 and endsWith(network.protocol, "tcp") ]
  [ file where event.action == "open"
      and (file.name like "*wifi*" or file.name like "*device*"
           or file.name like "*config*") ]
  [ network where event.action == "connection" and direction == "outbound"
      and destination.ip != "127.0.0.1" ]

Splunk SPL Query

index=main sourcetype=linux_secure OR sourcetype=syslog
| search process AND ("wifi" OR "wlan" OR "device_info" OR "mac" OR "serial")
| stats count by host, user, process, parent_process
| where count > 5
| table _time host user process parent_process count

index=main sourcetype=flow OR sourcetype=netflow
| search dst_port>=1024 OR (dest_ip AND bytes_out > 1000)
| stats sum(bytes_out) as bytes_out, dc(dest_ip) as dst_count by src_ip
| where dst_count > 3 AND bytes_out > 100000
| convert ctime(_time) as time
| table time src_ip dst_count bytes_out

Wazuh OSSEC Rule

<group name="cve-2021-26278,wifi,info-leak,">
    <rule id="262780" level="10">
        <if_sid>510</if_sid>
        <match>wifi|wlan|device_info|serial|mac</match>
        <regex>(\b(wifi|wlan)\b.*\b(info|status)\b)|(\b(serial|mac)\b.*\b(get|read|open)\b)</regex>
        <description>Possible CVE-2021-26278 WiFi module information disclosure - unauthorized device-info access</description>
        <group>attacker,recon,confidentiality,</group>
        <mitre>
            <id>T1005</id>
        </mitre>
    </rule>
</group>

Mitigation & Patch Guidance

Patch status context: the CNA claims a fix exists (confidence 2/4 — single source, not independently confirmed). No patched version, advisory, or diff has been made public, so the patch cannot be independently verified. Until Vivo publishes a confirmed advisory and firmware version, treat the device as potentially unpatched.

1. Immediate mitigations (defense-in-depth):

   • Inventory Vivo handsets in the environment; classify those on untrusted or home Wi-Fi as higher-risk.
   • Enforce local application vetting: restrict sideloading and unknown-source apps, since an installed malicious app is the most plausible local trigger.
   • Isolate Wi-Fi adjacent exposure by using enterprise WPA2/WPA3 with per-user credentials and client isolation enabled on corporate SSIDs.
   • Monitor device-facing network traffic for anomalous queries to high-numbered ports or unusual device-info response patterns (see Detection Guidance).

2. Patch/upgrade steps:

   • Subscribe to Vivo's official security-bulletin channel and check for an advisory addressing CVE-2021-26278.
   • Apply any released OTA/system update containing the WiFi module fix; verify the resulting firmware version against the vendor bulletin once published.
   • For BYOD fleets, enforce a minimum-firmware policy via MDM/EMM once a fixed build is identified.

3. Long-term hardening:

   • Require the vendor (Vivo) to publish a proper advisory with affected hardware generations, fixed build numbers, and a technical description of the permission-control correction.
   • At the architecture level, advocate for default-deny permission models on all module interfaces and for boundary security (kernel/TrustZone-level) that prevents user-space applications from reaching radio-module interfaces without explicit, capability-gated authorization.
   • Periodically re-evaluate CISA KEV status and EPSS trends for CVE-2021-26278; escalate priority if exploitation-in-the-wild evidence appears.

References

1. NVD — CVE-2021-26278: https://nvd.nist.gov/vuln/detail/CVE-2021-26278
2. CVE.org Record — CVE-2021-26278: https://www.cve.org/CVERecord?id=CVE-2021-26278
3. MITRE ATT&CK — T1005 Data from Local System: https://attack.mitre.org/techniques/T1005/
4. MITRE CWE — CWE-200 Exposure of Sensitive Information: https://cwe.mitre.org/data/definitions/200.html

No public vendor advisory (Vivo) was identified in the available data; the CNA is the sole source of the patch claim. No researcher blog or exploit-database write-up is documented. CISA KEV status is NO — the vulnerability has not been added to the Known Exploited Vulnerabilities catalog, and no threat-actor campaign or in-the-wild exploit evidence is currently reported.