Authenticated OS command injection in GR140DG ping diagnostic handler (root context)

Advisory metadata

CVSS v3.1 vector

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

CWE

CWE-78 — Improper Neutralization of Special Elements used in an OS Command

Vendor

ALTICE LABS / SFR France

Discovery

2026-01-08

Vendor notified

2026-01-15

Public disclosure

2026-05-04

Affected products

Summary

The ping diagnostic feature exposed by /bin/httpd_clientside on the ALTICE LABS / SFR France GR140DG fibre router passes user-controlled input into a shell command executed via system(). Input validation is character-based and not context-aware for shell execution, so command-substitution constructs are evaluated by the shell. The WebUI runs as root, so successful exploitation yields authenticated root-level remote command execution on the device.

Impact

An authenticated WebUI user can execute arbitrary shell commands as root on the router. Because the GR140DG is the default fibre CPE issued to a large population of SFR Fibre customers in France, the aggregate exposure is significant.

• Confidentiality: critical — read access to all on-device files, including credentials and configuration.
• Integrity: critical — arbitrary modification of router state, firmware persistence opportunities, and downstream-network tampering.
• Availability: critical — ability to disrupt service or render the device inoperable.
• Lateral-movement potential from LAN-resident malware or compromised WebUI credentials.

Technical details

The handler for /ping.cmd constructs a shell command of the form below and executes it through system(), which invokes /bin/sh and therefore performs full shell parsing and expansion before the executable is launched.

/bin/ping -c <count> -i <interval> -s <size> "<destAddr>" > /tmp/ptin_diag_result 2>&1

The destAddr parameter is interpolated directly into the command string. Validation is performed by URIStringValidation() (imported from librdk_dal.so), which filters characters rather than enforcing semantics. It rejects whitespace, control characters, double-quotes, backslash and percent, but permits the shell metacharacters used in command-substitution constructs. Because shell expansion happens before word-splitting, blocking whitespace alone does not prevent shell evaluation of the substituted output.

A stricter validator, hostnameStringValidation(), is present in the same codebase and enforces DNS hostname syntax (letters, digits, -, .) without permitting shell metacharacters. The ping handler does not use it. The WebUI process additionally runs with uid=0, removing any privilege containment around the shell call.

The root cause is a combination of an unsafe execution primitive (system()), the wrong validator for the context, and an over-privileged execution environment — a design flaw rather than a single missing check.

Proof of concept

Status

Withheld

Rationale

A working Python PoC reliably triggers the issue against the firmware versions listed above and is held privately. It will be released no earlier than 30 days after a vendor fix is generally available, or sooner if exploitation is observed in the wild. Defenders, the vendor and downstream ISPs may request access via PGP-signed email to info@xerod.io.

Remediation and mitigation

1. Apply firmware 3GN8020803R0B or later. The vendor has shipped a fix in this release. Operators should confirm their CPE has been updated; SFR-managed devices typically receive the update over the operator-controlled provisioning channel.
2. Configuration workaround (for devices that have not yet received the fix). Restrict WebUI access to the LAN, rotate WebUI credentials, and disable remote management. This does not remediate the underlying flaw but reduces exposure to compromised credentials and CSRF chaining.
3. Compensating control. Network segmentation between the router management interface and untrusted LAN devices, plus monitoring for anomalous outbound traffic from the CPE.

Disclosure timeline

Credit

xerod research. Reported to ALTICE LABS / SFR France on 2026-01-15.

Revision history

Artifacts

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