CVE-2017-2850

Executive Summary

CVE-2017-2850 affects the web management interface of Foscam C1 Indoor HD cameras running application firmware 2.52.2.37. The vulnerability allows a remote attacker to inject arbitrary characters into the pureftpd.passwd file during a username change operation via a specially crafted HTTP request, which subsequently enables bypassing chroot restrictions in the FTP server. With a CVSS score of 8.8 and an EPSS percentile in the 80.8th percentile of exploited CVEs, this represents a high-severity, high-probability-of-exploitation vulnerability in an internet-connected IoT device. The device is confirmed unpatched across all tracked sources, leaving affected cameras permanently exposed to this attack vector.

Technical Analysis

The vulnerability resides in the web management interface of the Foscam C1 Indoor HD camera, specifically within the username change functionality. The NVD description indicates that the flaw permits injection of arbitrary characters into the pureftpd.passwd file. This file is the password database used by the Pure-FTPd FTP server, which the camera exposes for file management operations.

The attack mechanism is best understood as a character injection / command injection class vulnerability. When a user initiates a username change through the web management interface, the application constructs or modifies an entry in pureftpd.passwd without adequately sanitizing the input. A specially crafted HTTP request can embed arbitrary characters — typically newline characters (\n or \r\n) — into the file. This allows an attacker to append or modify FTP user account entries within the file.

The security impact of this injection is the ability to bypass chroot restrictions imposed by the FTP server. Pure-FTPd enforces chroot jails on a per-user basis, typically configured through the ./ prefix in the user's home directory field within the passwd file. By injecting characters that modify the home directory specification or add new user entries without chroot constraints, an attacker can escape the intended file-system sandbox and gain access to broader portions of the device's file system or configuration.

The attack surface is the HTTP-based web management interface, which on many Foscam devices is exposed on port 80 (and sometimes 443) and is frequently accessible from the Internet due to improper network segmentation. The interface typically supports basic authentication, but an attacker who can reach the interface may be able to exploit this flaw without prior authentication if the username change endpoint is improperly protected, or may leverage weak/default credentials to authenticate first.

Insufficient technical detail is available regarding the exact HTTP endpoint, parameter names, or input handling logic, as the NVD description does not specify these implementation details. The vulnerability class, however, is clearly established: injection of arbitrary characters into a server-side FTP configuration/password file via an HTTP request, leading to chroot bypass.

Exploitation Scenarios

No public PoC is available; the attack chain below is inferred from the vulnerability class and NVD description.

Step 1: Reconnaissance / Target Identification

An attacker identifies vulnerable Foscam C1 cameras by scanning for exposed web management interfaces. Shodan and similar search engines routinely index these devices because they are often left accessible on the Internet with default credentials. The attacker may also use port scanning across IP ranges to identify HTTP services, then fingerprint the device as a Foscam C1 by examining HTTP response headers, the login page structure, or the firmware version returned by the device.

Step 2: Triggering the Flaw

The attacker sends a crafted HTTP request to the username change functionality of the web management interface. Because the application does not sanitize user-supplied characters, the attacker includes payload characters (e.g., %0a for newline, or %0d%0a for CRLF) in the username field. This causes the application to write arbitrary characters into the pureftpd.passwd file during the update operation.

Step 3: Payload Execution at Vulnerability-Class Level

At the vulnerability-class level, the injection payload is designed to modify the FTP user database in one of two ways:

• Append a new user entry: The attacker injects a newline followed by a complete FTP user record (username, password hash, UID, GID, home directory, shell) that lacks the chroot-restricting ./ prefix in the home directory field.
• Modify an existing entry: The attacker alters the home directory field of an existing account to remove the chroot restriction.

After the injection succeeds, the attacker authenticates to the FTP service using the newly created or modified account.

Step 4: Post-Exploitation Impact

With chroot restrictions bypassed, the attacker gains FTP access to directories outside the intended web-accessible file system. This provides the ability to:

• Read and modify system configuration files
• Extract sensitive credentials or device data
• Potentially achieve remote code execution by overwriting configuration files or binaries that are re-read on reboot
• Use the compromised device as a pivot point for lateral movement or as a member of a botnet

Impact Assessment

Business Impact: Foscam C1 cameras are consumer-grade IP surveillance devices. A successful exploitation grants an attacker unauthorized FTP access to the device's file system, enabling configuration tampering, credential theft, and potentially disabling the surveillance function entirely. For businesses that deploy these cameras for physical security monitoring, the impact includes loss of surveillance integrity and potential physical security blind spots.

CVSS Score: 8.8 (High) — While the exact CVSS vector is not provided, the score of 8.8 typically corresponds to a network-exploitable vulnerability with high impact on confidentiality, integrity, and availability, requiring no or minimal user interaction. The high score reflects the remoteness of the attack, the low complexity of exploitation, and the significant impact of chroot bypass leading to full file system access on the device.

Affected Systems: Foscam C1 Indoor HD cameras running application firmware 2.52.2.37. No official patches are available. Affected devices may be present in both consumer homes and small-to-medium business environments.

Blast Radius: The immediate blast radius is limited to the individual camera device (full file system compromise). However, the broader risk includes:

• Persistence: The attacker can maintain persistent access through FTP backdoors.
• Network pivot: Compromised cameras on a corporate network can be used to attack other internal hosts.
• Botnet recruitment: IoT devices such as this are prime targets for Mirai-style botnets.

EPSS and KEV Context: EPSS score of 0.02194 (80.8th percentile) indicates elevated probability of exploitation in the wild relative to other CVEs. The CISA KEV catalog does not list this CVE, meaning there is no government-confirmed exploitation seen, but the high EPSS percentile suggests attackers are aware of and potentially targeting this vulnerability class.

Detection Guidance

The following detection rules are designed to identify exploitation attempts against Foscam C1 cameras. Given the absence of known specific payloads, these rules focus on anomalous HTTP requests to the web management interface and suspicious FTP activity patterns.

Sigma Rule

title: Foscam C1 Web Interface - Username Change with Injection Attempt
id: 8f2c9a1e-57b3-4d1c-9e7a-3b6c2e8f0a11
status: experimental
description: Detects crafted HTTP requests to Foscam C1 cameras attempting character injection in username change operations, targeting the pureftpd.passwd file.
author: valtersit.com Threat Intelligence Team
date: 2024/01/15
logsource:
  category: webserver
  product: foscam
detection:
  selection_http_method:
    - cs-method: 'POST'
  selection_path:
    - cs-uri-path|contains: 'cgi-bin'
    - cs-uri-path|contains: 'user'
    - cs-uri-path|contains: 'account'
  selection_injection:
    - cs-uri-query|contains|all:
        - '%0a'
        - '%0d'
    - cs-uri-query|contains:
        - 'pureftpd'
        - 'passwd'
  selection_user_agent:
    cs-user-agent|contains|all:
      - 'curl'
      - 'wget'
  condition: selection_http_method and selection_path and selection_injection
  timeframe: 10s
falsepositives:
  - Legitimate administrative changes containing URL-encoded newlines (extremely rare)
level: high
tags:
  - attack.t1190
  - attack.t1213
  - cve.2017-2850

YARA Rule

rule Foscam_C1_CVE_2017_2850_HTTP_Injection
{
    meta:
        author = "valtersit.com Threat Intelligence Team"
        description = "Detects HTTP requests targeting Foscam C1 username change with encoded injection characters"
        cve = "CVE-2017-2850"
        date = "2024-01-15"
        severity = "high"

    strings:
        $s1 = "pureftpd.passwd" ascii wide nocase
        $s2 = "username" ascii wide nocase
        $s3 = "change" ascii wide nocase
        $s4 = "%0a" ascii
        $s5 = "%0d" ascii
        $s6 = "Foscam" ascii wide nocase
        $s7 = "C1" ascii wide nocase

    condition:
        any of ($s1, $s2, $s3) and
        any of ($s4, $s5) and
        (any of ($s6, $s7) or filesize < 10KB)
}

Suricata IDS Rule

alert http any any -> $HOME_NET any (msg:"ET EXPLOIT Foscam C1 CVE-2017-2850 FTP passwd Injection Attempt"; flow:to_server,established; content:"POST"; http_method; content:"cgi-bin"; http_uri; content:"%0a"; http_uri; content:"%0d"; http_uri; reference:cve,2017-2850; classtype:attempted-admin; sid:2027015; rev:1; metadata:attack_target IoT, deployment Perimeter, signature_severity Major, created_at 2024_01_15, tag cve_2017_2850;)

Note: This signature matches on URL-encoded CRLF characters in HTTP POST requests directed at CGI endpoints. Some legitimate applications may use %0d%0a for formatting; however, in the context of a camera management interface, this alone is suspicious. Adjust the content patterns to match the specific URI patterns of the Foscam web interface if discovered.

Elastic Detection

// Elastic EQL query to detect Foscam C1 injection attempts
sequence by source.ip, destination.ip with maxspan=5s
  [ network where network.protocol == "http" and
    http.request.method == "POST" and
    http.request.uri.text contains "cgi-bin" and
    (http.request.uri.text contains "%0a" or http.request.uri.text contains "%0d") ]
  [ file where file.name == "pureftpd.passwd" and
    (file.path contains "/etc" or file.path contains "/usr/local/etc") ]

Note: The file event portion requires that file system monitoring is enabled on the camera device or that a syslog/EDR agent is forwarding file-change events. In practice, this second event may not be available for embedded IoT devices; in that case, rely on the network-level HTTP detection alone.

Splunk SPL Query

index=web OR index=proxy
  (sourcetype="access_combined" OR sourcetype="iis" OR sourcetype="pan:traffic")
  method="POST"
  AND uri_path=*cgi-bin*
  AND (uri_query=*%0a* OR uri_query=*%0d*)
  AND (uri_query=*username* OR uri_query=*user* OR uri_query=*account*)
  | stats count by src_ip, dest_ip, uri_path, uri_query, status
  | where count > 3
  | table _time, src_ip, dest_ip, uri_path, uri_query, status, count

Wazuh OSSEC Rule

<group name="foscam,exploit,cve_2017_2850,">
  <rule id="117675" level="14">
    <decoded_as>json</decoded_as>
    <field name="url">\.cgi-bin\..*</field>
    <field name="url" type="pcre2">(?i)(%0a|%0d|%0D%0A|%250a)</field>
    <description>Foscam C1 CVE-2017-2850 - FTP passwd injection attempt detected via URL encoding</description>
    <group>foscam_exploit_attempt,</group>
    <mitre>
      <id>T1190</id>
    </mitre>
    <options>no_full_log</options>
  </rule>
</group>

Mitigation & Patch Guidance

Patch Confidence: 0/4 — UNPATCHED. No patch evidence exists from any tracked source. The vendor has not released a firmware update addressing this vulnerability.

1. Immediate Mitigations (Do these now)

• Network isolation: Place Foscam C1 cameras on a separate VLAN or network segment with no direct Internet exposure. If remote access is required, restrict it to VPN connections only.
• Port filtering: Block inbound access to the camera's web management interface (HTTP/HTTPS) and FTP ports from the Internet at the perimeter firewall. Allow management traffic only from trusted administrative IP addresses.
• Disable FTP if unused: If the FTP service is not required for camera operations, disable it via the management interface or firewall rules.
• Change default credentials: Ensure the administrative password for the web interface is changed from the default to a strong, unique password. This does not prevent exploitation of CVE-2017-2850 if the endpoint is unauthenticated, but it reduces the attack surface.
• Monitor outbound traffic: Enable logging on the firewall for traffic from camera IPs to detect anomalous FTP or management activity.

2. Patch/Upgrade Steps

• Check for firmware updates: Visit the Foscam official website or contact Foscam support to check for any firmware releases newer than 2.52.2.37. As of this report, no patch exists.
• Plan hardware replacement: Because the device is confirmed unpatched, the only reliable long-term remediation is replacing affected C1 cameras with newer models that receive active security updates.
• If replacement is not feasible: Treat the camera as permanently compromised and deploy it in a monitored, isolated network segment with aggressive egress filtering.

3. Long-Term Hardening

• Vendor accountability: Pressure the vendor (Foscam) for a security fix, referencing CVE-2017-2850 and the lack of any patch.
• Procurement policy: Adopt a procurement policy that requires IoT vendors to provide a minimum support lifecycle with security patch commitments.
• Segmentation best practice: Always place IoT devices and OT equipment on isolated subnets with strict firewall rules. Never expose management interfaces of embedded devices directly to the Internet.
• Firmware integrity monitoring: Where feasible, use network intrusion detection (Suricata/Snort) and log aggregation to detect attempts to exploit this flaw.
• Decommission end-of-life devices: Establish an asset lifecycle process to identify and retire devices that no longer receive security patches.

References

1. NVD Entry: https://nvd.nist.gov/vuln/detail/CVE-2017-2850 — Official NVD record with the CVE description, CVSS score, and status information.
2. Foscam Official Website: https://www.foscam.com — Vendor site for firmware releases and support. (No advisory for this CVE was found at publication time.)
3. CISA Known Exploited Vulnerabilities Catalog: https://www.cisa.gov/known-exploited-vulnerabilities-catalog — CVE-2017-2850 is not listed in the KEV catalog as of this report date.
4. EPSS (Exploit Prediction Scoring System): https://www.first.org/epss/ — EPSS score of 0.02194 indicates elevated (80.8th percentile) probability of exploitation in the wild.
5. Exploit-DB / Exploit-Database: https://www.exploit-db.com — Search for "Foscam C1" for any public exploit research. As of this report, no public PoC is known to be available.

Threat Actor Campaign Evidence: No confirmed threat actor campaigns have been publicly attributed to CVE-2017-2850 as of this report. However, the high EPSS percentile suggests the vulnerability class is being actively targeted, likely as part of broad IoT scanning and botnet recruitment campaigns (e.g., Mirai variants). The lack of CISA KEV listing does not preclude exploitation; it only reflects the absence of government-confirmed incidents. Security teams should treat any Foscam C1 camera accessible from untrusted networks as a high-risk asset.