CVE-2016-20088

Executive Summary

CVE-2016-20088 is a privilege escalation vulnerability in Comodo Chromodo Browser version 52.15.25.664, specifically affecting the ChromodoUpdater service. The service runs with SYSTEM privileges and is registered with an unquoted service path, allowing a low-privileged local attacker to place a malicious executable in a directory that will be resolved as part of the service binary path. Upon service restart or system reboot, the attacker's binary executes with SYSTEM integrity, resulting in full local compromise. The vulnerability remains unpatched, and no vendor fix is available, making affected installations permanently exposed.

Technical Analysis

The vulnerability falls into the unquoted service path class (CWE-428: Unquoted Search Path or Element), a well-known Windows privilege escalation flaw. When a Windows service is registered with a binary path containing spaces but lacking quotation marks, the Service Control Manager (SCM) resolves the path using a deterministic, hierarchical search algorithm. For a path like C:\Program Files\Comodo\Chromodo Updater\chromodo_update.exe (hypothetical example), Windows will attempt to execute each of the following paths in sequence:

1. C:\Program.exe
2. C:\Program Files\Comodo.exe
3. C:\Program Files\Comodo\Chromodo.exe
4. C:\Program Files\Comodo\Chromodo Updater\chromodo_update.exe (the intended binary)

If an attacker has write access to any directory earlier in that resolution chain (e.g., C:\ or C:\Program Files\Comodo\), they can plant a malicious executable matching one of the truncated names (e.g., Program.exe on C:\). When the service is restarted, SCM will execute the planted binary instead of the legitimate service executable.

In this specific case, the ChromodoUpdater service runs with SYSTEM privileges — the highest integrity level on Windows. This is a critical amplifier: the flaw itself is trivial (placement of a file in a writable directory), but the executing context transforms it into complete kernel-level compromise. The NVD description confirms the service runs "with SYSTEM privileges" and that a local attacker can "execute arbitrary code with elevated privileges upon service restart or system reboot."

The attack surface is entirely local. No network component exists in the vulnerability itself; however, the prerequisite is that the attacker must already have a foothold on the target system — either as an unprivileged user, or via a separate remote exploit that delivers an initial payload. The unquoted path flaw then serves as the privilege escalation step.

No specific file paths, registry keys, or executable names beyond the service name (ChromodoUpdater) and the general mechanism are disclosed in the NVD description. The vendor has not released technical documentation of the vulnerable path, and no public PoC or exploit code is available. The precise directory structure is therefore unknown; however, the attack mechanism is well-established and reproducible across Windows versions.

Version scope: The CNA title and NVD description reference specifically version 52.15.25.664. No other affected versions are listed. It is plausible that other builds of Chromodo Browser share the flaw, but insufficient technical detail is available to confirm this. The product itself appears to be end-of-life; Comodo has not issued updates, and the Chromodo browser was discontinued.

Exploitation Scenarios

No public PoC is available for CVE-2016-20088; the following attack chain is inferred from the vulnerability class (unquoted service path) and the NVD description.

Step 1 — Reconnaissance/Initial Access: The attacker must already have local access to the target system, typically as an unprivileged user. This could result from a phishing campaign, a dropper delivered via malicious document, or a remote code execution flaw elsewhere in the stack. Once present, the attacker enumerates locally installed services, looking for unquoted service paths with SYSTEM privileges. Tools commonly used include wmic service get name,displayname,pathname or PowerShell's Get-CimInstance Win32_Service. The attacker identifies the ChromodoUpdater service as a candidate.

Step 2 — Triggering the Flaw: The attacker inspects the resolved path of ChromodoUpdater and determines which directory in the unquoted path chain is writable by the current user. Common weak spots include the root of the boot volume (C:\), where a default user may have create-directory or file-write permissions, or a poorly permissioned subdirectory under C:\Program Files. The attacker plants a malicious executable named to match one of the path components — for example, if the service path is C:\Program Files\Comodo\Chromodo Updater\updater.exe, the attacker creates C:\Program.exe or C:\Program Files\Comodo.exe.

Step 3 — Payload Execution: The attacker forces a service restart. If the attacker holds SeShutdownPrivilege or reboot rights (common for standard users on Windows), they can schedule a shutdown/reboot with shutdown /r. Alternatively, they can use sc stop ChromodoUpdater and sc start ChromodoUpdater if the service can be manually controlled. On restart, SCM resolves the unquoted path, finds the planted executable first, and executes it in the SYSTEM context. The payload can be a reverse shell, a new administrative account creation, a credential dump, a keylogger, or any other locally privileged operation.

Step 4 — Post-Exploitation Impact: With SYSTEM integrity, the attacker has full control over the host: they can read any file, patch memory of any process, load kernel drivers, disable security software, extract domain credentials from LSASS, and move laterally across the enterprise network using stolen tokens. The compromise is persistent if the attacker survives the reboot (e.g., by planting a persistent service or scheduled task) or if the malicious binary itself replaces the original updater on subsequent service restarts.

Impact Assessment

CVSS Score: 8.5 out of 10. The vector reflects a high-severity local privilege escalation: low attack complexity, local access required, low privileges needed, no user interaction, and a scope change from the attacker's user context to SYSTEM. The impact to confidentiality, integrity, and availability is each rated High.

Business Impact: Successful exploitation results in complete host takeover. For enterprise organizations running Chromodo Browser on end-user workstations or virtual desktop infrastructure, any user with local access — including infected machines from phishing campaigns — can escalate to SYSTEM. This undermines endpoint security controls, Active Directory trust boundaries, and data classification efforts. The unpatched nature of the flaw means affected machines carry a permanent residual risk.

Affected Systems: Comodo Chromodo Browser 52.15.25.664. The product is discontinued, so no future builds will receive corrective updates. Additional Chromodo builds might be affected but are not confirmed. Enterprise environments that standardized on Chromodo for web isolation or compliance purposes are the most severely exposed.

Blast Radius: Local-only at initial exploitation, but the SYSTEM-level foothold enables lateral movement using credential harvesting and Pass-the-Hash techniques. In a flat network architecture, this single host compromise can cascade to domain-wide compromise. The blast radius is therefore bounded by network segmentation and AD tiering policies.

CISA KEV Status: The vulnerability is NOT listed in CISA's Known Exploited Vulnerabilities catalog, and the EPSS score is low (0.00175, placing it in the 7.2nd percentile of exploited CVEs). This suggests no observed in-the-wild exploitation yet; however, the unpatched status and trivial exploitation mechanism make it a credible target for opportunistic attackers, especially in environments that still run Chromodo.

Detection Guidance

Detection of this vulnerability is challenging because the exploitation is purely local and involves writing a file to disk and restarting a service — actions that are not inherently network-detectable. The rules below focus on the artifacts of the attack: suspicious file creation in service-path directories, service control events, and process execution anomalies.

Sigma Rule

title: Unquoted Service Path Privilege Escalation - ChromodoUpdater
id: 7a9c3f2e-8d1b-4c6a-9e5f-1b2c3d4e5f60
status: experimental
description: Detects creation of executables in directories that could be exploited by the unquoted ChromodoUpdater service path, or execution of suspicious binaries at system startup.
references:
    - https://nvd.nist.gov/vuln/detail/CVE-2016-20088
author: valtersit.com Threat Intelligence Team
date: 2025/01/14
logsource:
    category: process_creation
    product: windows
detection:
    selection_process:
        Image|endswith:
            - '\Program.exe'
            - '\Program Files\Comodo.exe'
            - '\Program Files\Comodo\Chromodo.exe'
        User: 'NT AUTHORITY\SYSTEM'
    selection_file_create:
        EventID: 11  # File creation (Sysmon)
        TargetFilename|endswith:
            - '\C:\Program.exe'
            - '\C:\Program Files\Comodo.exe'
            - '\C:\Program Files\Comodo\Chromodo.exe'
    condition: selection_process or selection_file_create
    timeframe: 5m
level: high
falsepositives:
    - Legitimate executables named similarly in the same directories (unlikely but possible).
tags:
    - attack.privilege_escalation
    - attack.t1574
    - cve.2016-20088

YARA Rule

rule CVE_2016_20088_Unquoted_Service_Path_Chromodo
{
    meta:
        author = "valtersit.com Threat Intelligence Team"
        description = "Detects executable files planted to exploit the unquoted ChromodoUpdater service path (CVE-2016-20088)"
        cve = "CVE-2016-20088"
        date = "2025-01-14"
        severity = "high"

    strings:
        $susp_path1 = "C:\\Program.exe" ascii wide
        $susp_path2 = "C:\\Program Files\\Comodo.exe" ascii wide
        $susp_path3 = "C:\\Program Files\\Comodo\\Chromodo.exe" ascii wide
        $susp_path4 = "C:\\Program Files\\Comodo\\Chromodo Updater\\" ascii wide
        $service_name = "ChromodoUpdater" ascii wide nocase

    condition:
        uint16(0) == 0x5A4D and           // MZ header
        any of ($susp_path*) and $service_name
}

Suricata IDS Rule

alert http any any -> any any (
    msg:"CVE-2016-20088 - Attempted Download of Chromodo Privilege Escalation Payload";
    flow:established,to_client;
    content:"ChromodoUpdater"; nocase;
    content:"exe"; distance:2048;
    classtype:attempted-admin;
    sid:20260088;
    rev:1;
    metadata:cve CVE-2016-20088;
)

Elastic Detection

sequence with maxspan=5m
  [file where event.action == "creation" and
   (file.path == "C:\\Program.exe" or
    file.path == "C:\\Program Files\\Comodo.exe" or
    file.path == "C:\\Program Files\\Comodo\\Chromodo.exe") and
   file.extension == "exe"]
  [process where user.name == "SYSTEM" and
   (process.name == "Program.exe" or
    process.name == "Comodo.exe" or
    process.name == "Chromodo.exe")]

Splunk SPL Query

index=windows sourcetype=WinEventLog:Security OR sourcetype=XmlWinEventLog
| search EventCode=4688 OR EventCode=1
| where (User="NT AUTHORITY\\SYSTEM" AND (New_Process_Name="*\\Program.exe" OR New_Process_Name="*\\Comodo.exe" OR New_Process_Name="*\\Chromodo.exe"))
| table _time, host, User, New_Process_Name, CommandLine
| sort - _time

Wazuh OSSEC Rule

<group name="windows,system_events,">
  <rule id="100288" level="12">
    <if_sid>5715</if_sid>
    <field name="win.system.eventID">4688</field>
    <match>Program.exe|Comodo.exe|Chromodo.exe</match>
    <description>CVE-2016-20088 - Potential unquoted service path exploitation - SYSTEM process spawned from suspicious path</description>
    <groups>privilege_escalation</groups>
    <mitre>
      <id>T1574</id>
    </mitre>
  </rule>
</group>

Mitigation & Patch Guidance

Patch Confidence: 0/4 — UNPATCHED. No vendor fix, no third-party patch, and no workaround has been published for CVE-2016-20088. Comodo has not acknowledged the vulnerability, and Chromodo Browser appears to be end-of-life with no future maintenance releases expected.

Immediate Mitigations (do these now):

1. Uninstall Chromodo Browser from all systems. This is the only definitive remediation. Since the product is discontinued, there is no reason to retain it in any enterprise environment.
2. If uninstallation is not immediately feasible, disable the ChromodoUpdater service via Group Policy or manual intervention: sc config ChromodoUpdater start= disabled. This prevents the service from restarting and therefore prevents the privilege escalation trigger.
3. Restrict write permissions on the root of the boot volume (C:\) and on all directories under C:\Program Files to Administrators only. Audit existing ACLs to identify any overly permissive entries using icacls.
4. Enforce application whitelisting (e.g., AppLocker or WDAC) to block execution of binaries named Program.exe, Comodo.exe, or Chromodo.exe unless signed by Comodo.

Patch/Upgrade Steps:

• No patch exists. Migrate to a supported browser (e.g., standard Chromium, Firefox ESR, or Microsoft Edge) and implement the same web isolation requirements using supported technologies if isolation was the reason for Chromodo adoption.

Long-Term Hardening:

1. Adopt a standard for Windows service configuration: ensure all new service deployments use quoted paths in the registry (HKLM\SYSTEM\CurrentControlSet\Services\<Name>\ImagePath).
2. Baseline host configuration with CIS Benchmarks, which include checks for unquoted service paths (CIS Control 18.6).
3. Deploy Sysmon with configuration to log file creation on critical directories and process creation, feeding into the detection rules above.
4. Segment the network to limit blast radius from local privilege escalation events. Implement tiered AD administration to prevent lateral movement from compromised workstations.
5. Inventory and retire end-of-life software as part of a formal asset lifecycle process. Chromodo's discontinuation was the root cause of the permanent exposure.

References

1. NVD Entry — CVE-2016-20088: https://nvd.nist.gov/vuln/detail/CVE-2016-20088 — Official NVD description of the vulnerability, including the CNA title and affected version.
2. CWE-428 — Unquoted Search Path or Element: https://cwe.mitre.org/data/definitions/428.html — MITRE Common Weakness Enumeration entry describing the flaw class exploited by this CVE.
3. MITRE ATT&CK Technique T1574 — Hijack Execution Flow: https://attack.mitre.org/techniques/T1574/ — Describes the general technique class encompassing unquoted path exploitation.
4. CISA Known Exploited Vulnerabilities Catalog: https://www.cisa.gov/known-exploited-vulnerabilities-catalog — Confirms CVE-2016-20088 is NOT listed as a KEV as of January 2025.
5. vulners.com CVE record: https://vulners.com/cve/CVE-2016-20088 — Aggregated references and metadata corroborating the unpatched status.

Threat Actor Activity: No known threat actors have been publicly attributed to exploiting CVE-2016-20088 as of the writing of this report. The absence of in-the-wild evidence and low EPSS percentile indicates that exploitation has not been widespread; however, the unpatched status and the simplicity of the flaw mean it remains viable for future attacks, particularly in environments where Chromodo is still present.