D-Link DSL2730U router restricted telnet shell command whitelisting bypass

Overview

D-Link DSL2730U routers contain a restricted telnet shell with limited allowed commands. An authenticated attacker can chain unauthorized commands through authorized commands in order to bypass the command whitelisting.

Description

CWE-78: Improper Neutralization of Special Elements used in an OS Command (‘OS Command Injection’):

D-Link DSL2730U routers contain a restricted telnet shell with limited allowed commands. Commands entered in the restricted telnet shell are executed by passing them as command parameters of execution “sh -c”, for example, “echo | ls” will result in passing a whitelisted command (echo) and executing “sh -c echo | ls” on the underlying Linux environment. The STDOUT output of the command execution is returned to the telnet terminal. An authenticated attacker can chain unauthorized commands through authorized commands in order to bypass the command whitelisting.

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Impact

An authenticated attacker can chain unauthorized commands through authorized commands in order to bypass the command whitelisting.

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Solution

We are currently unaware of a practical solution to this problem.

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Restrict Access

As a general good security practice, only allow connections from trusted hosts and networks. Restricting access would prevent an attacker from accessing an telnet interface using the affected credentials from a blocked network location.

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Vendor Information

876780

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D-Link Systems, Inc. Affected

Notified: November 01, 2012 Updated: December 03, 2012

Status

Affected

Vendor Statement

We have not received a statement from the vendor.

Vendor Information

We are not aware of further vendor information regarding this vulnerability.

CVSS Metrics

Group	Score	Vector
Base	6.8	AV:N/AC:L/Au:S/C:C/I:N/A:N
Temporal	5.2	E:POC/RL:W/RC:UC
Environmental	1.4	CDP:L/TD:L/CR:ND/IR:ND/AR:ND

References

<http://cwe.mitre.org/data/definitions/78.html&gt;

Acknowledgements

Thanks to Nikolay Dachev for reporting this vulnerability.

This document was written by Michael Orlando.

Other Information

CVE IDs:	CVE-2012-5966
Date Public:	2012-12-12 Date First Published: