Executive Summary

CVE-2026-31196 is a command injection vulnerability in the traceroute diagnostic feature of the ALTICE LABS / SFR France GR140DG and GR140IG fibre routers. The vulnerability occurs because the traceroute handler inserts unsanitized user input directly into a system() call. This means that authenticated remote attackers can craft malicious input in the destAddr parameter that uses shell command substitution to execute arbitrary commands with root privileges.

The root cause is improper input validation combined with the WebUI running as root, allowing attackers to execute commands as the highest privilege level on the device.

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Impact Analysis

Exploitation of this vulnerability can have severe impacts including unauthorized access to sensitive data, modification of router settings, disruption of network services, and potential lateral movement within the affected network.

• Attackers can gain root-level control over the router.
• Sensitive information stored or passing through the router can be exposed.
• Network configurations can be altered, potentially causing outages or degraded service.
• Attackers may use the compromised device as a foothold to attack other devices on the network.

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Detection Guidance

Detection of this vulnerability involves identifying attempts to exploit the traceroute diagnostic handler by sending crafted destAddr parameters containing shell command substitutions to the /bin/httpd_clientside service on affected ALTICE LABS / SFR France GR140DG and GR140IG routers.

Since the vulnerability requires authenticated access to the WebUI, monitoring authenticated HTTP requests to the traceroute diagnostic feature for unusual or suspicious input containing shell metacharacters (such as backticks, $(), or semicolons) can help detect exploitation attempts.

Specific commands to detect exploitation attempts could include inspecting web server logs or capturing network traffic to look for suspicious parameters. For example:

• Using grep on web server logs to find suspicious destAddr parameters: grep -E 'destAddr=.*[`$\(\);]' /var/log/httpd/access.log
• Using tcpdump or Wireshark to capture HTTP POST or GET requests to the traceroute endpoint and analyzing parameters for shell metacharacters.

Additionally, checking for unexpected or unauthorized command execution on the router itself may indicate exploitation.

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Mitigation Strategies

Immediate mitigation steps include applying the vendor-released firmware update version 3GN8020803R0B, which addresses this vulnerability.

Other recommended actions are restricting access to the WebUI to trusted users only and implementing network segmentation to limit exposure of the vulnerable device.

These steps help prevent authenticated attackers from exploiting the command injection flaw in the traceroute diagnostic handler.

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Compliance Impact

This vulnerability allows authenticated attackers to execute arbitrary commands as root on the affected routers, potentially leading to unauthorized access to sensitive data and modification of router settings.

Such unauthorized access and potential data compromise could negatively impact compliance with common standards and regulations like GDPR and HIPAA, which require protection of sensitive data and secure system configurations.

Exploitation could also lead to service disruption and lateral movement within the network, further increasing the risk of non-compliance due to failure to maintain system integrity and confidentiality.

Mitigation steps such as applying firmware updates, restricting WebUI access, and implementing network segmentation are critical to restore compliance and reduce risk.

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