CVE-2021-26279

Executive Summary

CVE-2021-26279 is a medium-severity information disclosure vulnerability (CVSS 5.9) in the Weather module of Vivo mobile devices. The issue stems from improper storage of certain module parameters, which can result in leakage of sensitive information to unauthorized local actors. Affected users include Vivo smartphone users running the proprietary Weather module; however, no specific affected versions have been disclosed by the vendor. Exploitation is likely limited to local access (e.g., a malicious or compromised application), and there is currently no evidence of in-the-wild exploitation (CISA KEV: no; EPSS: 0.00161, 5.7th percentile).

Technical Analysis

The CNA-supplied title identifies the vulnerability as an "Information disclosure vulnerability in Weather module," while the NVD description states that "some parameters of the weather module are improperly stored, leaking some sensitive information." This places the flaw in the vulnerability class of insecure storage of sensitive data, closely aligned with CWE-922 (Insecure Storage of Sensitive Information). The description strongly suggests that the Weather module persists runtime parameters — potentially including location coordinates, search queries, cached device identifiers, timestamps, or other contextual data — in a storage location that is accessible to processes or applications beyond the module's intended trust boundary.

No specific parameter names, file paths, database tables, or storage mechanisms are disclosed in the available CNA/NVD data. This severely limits code-level analysis. Based on the description alone, the attack surface is local rather than network-adjacent: on Android, Weather modules typically cache data in an application-private directory (e.g., /data/data/<package>/...), in SharedPreferences, or in SQLite databases. If these stores are created with excessive permissions, a second malicious app without privileges could read the records directly. Alternatively, the data may be copied into logs, backups, or cloud-synced payloads without proper sanitization.

Because the disclosure is described as "improperly stored," the root cause is most plausibly a design or implementation flaw — e.g., failing to mark cached weather data as sensitive, using world-readable file modes, or embedding sensitive parameters in plaintext within persistent configurations. The resulting impact is primarily confidentiality: local information disclosure up to the sensitivity of the parameters stored. No authentication bypass, code execution, or privilege escalation is indicated by the description. Insufficient technical detail is available to confirm the exact storage mechanism, the sensitive fields involved, or the local attack prerequisites (e.g., whether the data is readable by an unprivileged third-party app, by ADB, or via a backup stream).

The patch is only CLAIMED by the CNA with a patch confidence of 2/4; it has not been independently confirmed, and no fix version or reference has been made public. Security teams and researchers should treat the patch status as unverified and prioritize testing of any vendor-issued OTA or firmware update before deployment.

Exploitation Scenarios

No public PoC, exploit code, or Nuclei template exists for CVE-2021-26279. The following attack chain is therefore inferred from the vulnerability class of insecure information storage (CWE-922) and from the description supplied by Vivo (via the CNA). Specific implementation details should not be assumed where none are disclosed.

1. Reconnaissance / Target Identification. An attacker identifies a target Vivo device running the affected (but undisclosed) version of the Weather module. Since the attack surface is local, the primary reconnaissance step is determining whether the target has third-party applications installed or whether the attacker can deliver a malicious payload to the device. Social engineering or supply-chain delivery of a low-privilege Android application is the most plausible entry vector.

2. Triggering the Flaw. The attacker's application (or an authorized local process operating under an expanded trust context) queries the storage location used by the Weather module. Because the parameters were improperly stored — likely in plaintext and/or with insufficient access controls — the attacker does not need to bypass strong protection mechanisms. Elevation of privilege is not required if the storage permissions allow cross-application reads; otherwise, the attacker would first need to escalate context (e.g., via debugger access or a secondary vulnerability).

3. Payload / Execution Method at the Vulnerability-Class Level. At the class level, the "payload" is a read operation: enumerating files, databases, or preference stores associated with the Weather module, decoding or parsing the stored parameters, and copying the sensitive values to an attacker-controlled sink. Where the storage format is unknown, the attacker may brute-force or inspect the application's data directory structure. Because the parameters are improperly stored rather than improperly transmitted, no network payload is required to trigger the initial disclosure.

4. Post-Exploitation Impact. The exfiltrated parameters may include location history, device identifiers, timestamps, or other personal information. The attacker can use this data to profile the user, conduct targeted social engineering, or feed subsequent attacks (e.g., credential phishing leveraging observed location patterns). If the leaked parameters include authentication tokens or session identifiers, the impact escalates to account takeover — though no evidence supports this and the description lists only "some sensitive information." Finally, the attacker may exfiltrate the collected data over the network using standard HTTP/drop channels, at which point network-based detection may be possible.

Impact Assessment

The vulnerability has a CVSS base score of 5.9 (Medium); however, the absence of a published vector string (AV/AC/PR/UI scope) prevents precise calculation of sub-scores. Based on the description's implied threat model, confidentiality is the predominantly impacted security property; integrity and availability are not implicated by the NVD data. The medium score likely reflects that exploitation requires local access or the presence of a malicious co-resident application, lowering the attack vector relative to remote vulnerabilities, while the sensitivity of leaked device data elevates the confidentiality impact.

The blast radius is limited to the affected Vivo Weather module and the sensitive parameters it stores; it does not extend to other components unless chained. However, because no affected version range has been published, the entire Vivo device population running the Weather module must be considered potentially affected. Enterprise deployment of Vivo handsets (e.g., BYOD programs) is at elevated risk, as leaked location or device data may facilitate physical or persistent-targeting attacks. Based on the EPSS score (0.00161, 5.7th percentile), the exploitation probability is currently very low. No CISA KEV listing and no known threat-actor campaigns were identified as of the report date.

Detection Guidance

Detection for this vulnerability is challenged by a lack of public artifacts (file paths, package names, network indicators). The following detections therefore target the vulnerability class — local storage access and exfiltration patterns — and should be tuned to each environment.

Sigma Rule

title: Suspicious Access to Vivo Weather Module Data Storage
id: 0b4c6f3a-9e2d-4a1c-b8f7-2c5e9d1a7b02
status: experimental
description: Detects possible local reads of Weather-module data storage
             associated with CVE-2021-26279 (information disclosure).
             Class-level detection; tune paths per endpoint platform.
references:
    - https://nvd.nist.gov/vuln/detail/CVE-2021-26279
logsource:
    product: windows
    category: file_event
detection:
    selection_access:
        TargetFilename:
            - '*weather*'
            - '*vivo*weather*'
        EventID:
            - 11          # File create/read/write events in Sysmon context
    selection_sensitive:
        TargetFilename:
            - '*cache*'
            - '*log*'
            - '*pref*'
    condition: selection_access and selection_sensitive
falsepositives:
    - Legitimate system or application maintenance tasks touching files with "weather" in the name
level: medium

YARA Rule

rule CVE_2021_26279_Vivo_Weather_Data_Leak
{
    meta:
        author = "ValtersIT Threat Intelligence"
        description = "Detects artifacts containing Vivo weather-module data markers (class-level), e.g., exfiltrated dumps or local backups."
        cve = "CVE-2021-26279"
        date = "2026-05-07"
    strings:
        $kw_weather = "weather" ascii nocase
        $kw_lat     = "latitude" ascii nocase
        $kw_lon     = "longitude" ascii nocase
        $kw_time    = "timestamp" ascii nocase
        $kw_vivo    = "vivo" ascii nocase
        $kw_json    = "{ \"weather" ascii nocase
    condition:
        // Match likely dump or log files (text-like, moderate size)
        filesize < 10MB and
        2 of ($kw_lat, $kw_lon, $kw_vivo, $kw_weather) and
        any of ($kw_weather, $kw_json)
}

Suricata IDS Rule

alert http any any -> any any (msg:"CVE-2021-26279 Potential Vivo Weather Data Exfiltration";
    flow:to_server,established;
    content:"weather"; http.uri;
    pcre:"/(latitude|longitude|location|timestamp)/i";
    sid:202126279; rev:1; classtype:attempted-user; reference:cve,2021-26279;)

Elastic Detection

file where
  event.action in ("read", "open") and
  (file.name : "*weather*" or file.path : "*vivo*")

# Supplemental: flag outbound HTTP containing possible stolen weather-data parameters
network where
  network.direction : "egress" and
  network.protocol : "http" and
  process.name : ("*weather*", "*vivo*", "*chrome*")

Splunk SPL Query

index=endpoint (TargetFilename="*weather*" OR file_name="*weather*" OR process="*weather*")
| eval leaked_indicators = if(match(file_name, "(?i)(lat|lon|location|weather)"), 1, 0)
| stats count earliest(_time) latest(_time) by host, user, process_name, TargetFilename, leaked_indicators
| where leaked_indicators=1

Wazuh OSSEC Rule

<group name="cve-2021-26279,">
  <rule id="381935" level="7">
    <if_sid>550,553</if_sid>
    <syscheck path="/data/*/weather*" check_all="yes" />
    <description>CVE-2021-26279: access or modification of Vivo Weather module data storage (possible information disclosure)</description>
    <mitre>
      <id>T1005</id>
      <ref>https://nvd.nist.gov/vuln/detail/CVE-2021-26279</ref>
    </mitre>
  </rule>
</group>

Mitigation & Patch Guidance

Immediate Mitigations (until a verified patch is available):

1. Restrict third-party application installs on Vivo devices to trusted stores; disable "install unknown apps" permissions on browsers and messaging applications.
2. Harden the Weather module where possible: disable cloud sync of weather data, disable location-based weather personalization, and remove Weather module shortcuts/widgets on high-risk devices.
3. Review third-party apps for unnecessary permissions, especially access to storage, location, and device identifiers. Use Android's sandboxing and permission audit features or an EDR/MDM agent on managed devices.
4. Enable full-disk encryption and enforce strong device unlock policies to reduce the risk of physical-access extraction of the improperly stored parameters.

Patch / Upgrade Steps:

1. The CNA has CLAIMED a patch exists, but confidence is 2/4 — the single source is the CNA itself, and no version or commit has been published. Treat this as unconfirmed.
2. Periodically check for Vivo OTA/firmware updates for the affected Weather module. Apply official updates as soon as they are released by the vendor and verify the update includes a specific CVE-2021-26279 fix.
3. Subscribe to Vivo security bulletins and the CVE feed (NVD) for updates to the affected-version list or patch verification.

Long-Term Hardening:

1. Mandate vendor patch verification through MDM/UEM for any enterprise fleet containing Vivo devices; maintain a software bill of materials (SBOM) for mobile firmwares.
2. Standardize on least-privilege application policies and containerization for BYOD devices; separate work and personal profiles to limit lateral data access.
3. Integrate class-level detection rules (Sigma/YARA/EQL/SPL/Wazuh) into mobile and endpoint detection pipelines, so future disclosures of similar improper-storage flaws are caught early.

References

1. NVD — CVE-2021-26279 Detail: https://nvd.nist.gov/vuln/detail/CVE-2021-26279
2. CVE.org — CVE-2021-26279 Record: https://www.cve.org/CVERecord?id=CVE-2021-26279
3. MITRE ATT&CK — Technique T1005 (Data from Local System): https://attack.mitre.org/techniques/T1005/
4. FIRST — EPSS Data (CVE-2021-26279, score 0.00161): https://www.first.org/epss/

Known Exploitation Status: No in-the-wild exploitation, exploit code, or threat-actor campaigns were identified at the time of writing. CISA KEV does not list this CVE. Patch status remains unconfirmed (2/4 confidence, sole source: CNA).