Vulnerability Note VU#876780

D-Link DSL2730U router restricted telnet shell command whitelisting bypass

Original Release date: 12 Dec 2012 | Last revised: 12 Dec 2012

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.

Impact

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

Solution

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

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.

Vendor Information (Learn More)

VendorStatusDate NotifiedDate Updated
D-Link Systems, Inc.Affected01 Nov 201203 Dec 2012
If you are a vendor and your product is affected, let us know.

CVSS Metrics (Learn More)

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

Credit

Thanks to Nikolay Dachev for reporting this vulnerability.

This document was written by Michael Orlando.

Other Information

  • CVE IDs: CVE-2012-5966
  • Date Public: 12 Dec 2012
  • Date First Published: 12 Dec 2012
  • Date Last Updated: 12 Dec 2012
  • Document Revision: 7

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