CyberSecBulletin
CVE-2020-3161Exploited in the wildNVD status: Analyzed

Cisco IP Phones Web Server Remote Code Execution and Denial-of-Service

Published Updated By the CyberSecBulletin desk

CVE-2020-3161 is a critical-severity improper input validation vulnerability in Cisco IP phone from Cisco, with a CVSS 3.1 base score of 9.8 out of 10. It can be exploited remotely over the network by an unauthenticated attacker, without any action from a user. CISA added it to the Known Exploited Vulnerabilities catalogue on November 3, 2021, which means attacks have been observed in the wild.

Patch now

Attackers are already exploiting this vulnerability, according to CISA.

What to do

  1. Check which version of Cisco IP phone you run against the affected versions below, and install the vendor's latest release.
  2. CISA's required action: Apply updates per vendor instructions.
  3. Read the advisory on tools.cisco.com for workarounds and exact fixed builds.
  4. Until you can update, restrict network access to the affected service so it is not reachable from untrusted networks.

Affected products and versions

VendorProductAffected versionsFixed in
CiscoCisco IP phoneNot specified in the recordNot stated
CiscoIP Phone 8865 Firmware10.3\(1\)es14; 11.0\(1\); 11.0\(5\)sr1Not stated
CiscoIP Phone 8851 Firmware10.3\(1\)es14; 11.0\(1\); 11.0\(5\)sr1Not stated
CiscoIP Phone 7841 Firmware11.0\(1\)Not stated
CiscoIP Phone 7821 Firmware11.0\(1\)Not stated
CiscoIP Phone 8811 Firmware10.3\(1\)es14; 11.0\(1\); 11.0\(5\)sr1Not stated
CiscoIP Phone 8861 Firmware10.3\(1\)es14; 11.0\(1\); 11.0\(5\)sr1Not stated
CiscoIP Phone 8845 Firmware10.3\(1\)es14; 11.0\(1\); 11.0\(5\)sr1Not stated
CiscoIP Phone 7861 Firmware11.0\(1\)Not stated
CiscoIP Phone 8841 Firmware10.3\(1\)es14; 11.0\(1\); 11.0\(5\)sr1Not stated
CiscoIP Phone 7811 Firmware11.0\(1\)Not stated
CiscoIP Phone 8821 Firmware10.3\(1\)es14; 11.0\(1\); 11.0\(5\)sr1Not stated
CiscoIP Phone 8821-ex Firmware10.3\(1\)es14; 11.0\(1\); 11.0\(5\)sr1Not stated
Cisco8831 Firmware10.3\(1\)es14; 11.0\(1\); 11.0\(5\)sr1Not stated

Version data comes from the organisation that assigned the CVE. Confirm against the vendor advisory before deciding you are unaffected.

How the severity score breaks down

Attack vector
NetworkCan be exploited remotely over a network, including the internet.
Attack complexity
LowNo special conditions are needed; the attack works reliably.
Privileges required
NoneNo account or login is needed.
User interaction
NoneNo action by a victim is required.
Scope
UnchangedImpact stays within the vulnerable component.
Confidentiality
HighAll data handled by the component can be read.
Integrity
HighData or code can be modified at will.
Availability
HighThe component can be taken down completely.

Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H. Scored by NVD.

Scoring systemScoreSeverityScored by
CVSS 3.19.8CriticalNVD
CVSS 3.09.8CriticalCNA (cisco.com)
CVSS 2.010.0HighNVD

Official description

A vulnerability in the web server for Cisco IP Phones could allow an unauthenticated, remote attacker to execute code with root privileges or cause a reload of an affected IP phone, resulting in a denial of service (DoS) condition. The vulnerability is due to a lack of proper input validation of HTTP requests. An attacker could exploit this vulnerability by sending a crafted HTTP request to the web server of a targeted device. A successful exploit could allow the attacker to remotely execute code with root privileges or cause a reload of an affected IP phone, resulting in a DoS condition.

Source: the CVE record as published by its numbering authority, via NVD and CVE.org.

The underlying weakness: Improper Input Validation

The product receives input or data, but it does not validate or incorrectly validates that the input has the properties that are required to process the data safely and correctly.

How developers prevent this class of flaw

  • Consider using language-theoretic security (LangSec) techniques that characterize inputs using a formal language and build recognizers for that language. This effectively requires parsing to be a distinct layer that effectively enforces a boundary between raw input and internal data representations, instead of allowing parser code to be scattered throughout the program, where it could be subject to errors or inconsistencies that create weaknesses.
  • Use an input validation framework such as Struts or the OWASP ESAPI Validation API. Note that using a framework does not automatically address all input validation problems; be mindful of weaknesses that could arise from misusing the framework itself (CWE-1173).
  • Understand all the potential areas where untrusted inputs can enter the product, including but not limited to: parameters or arguments, cookies, anything read from the network, environment variables, reverse DNS lookups, query results, request headers, URL components, e-mail, files, filenames, databases, and any external systems that provide data to the application. Remember that such inputs may be obtained indirectly through API calls.

More Improper Input Validation vulnerabilities (CWE-20)

Timeline

  1. CVE record published.
  2. Added to CISA's Known Exploited Vulnerabilities catalogue.
  3. Deadline for US federal agencies to remediate, set by CISA.
  4. CISA published its SSVC assessment (exploitation: active, automatable: yes, technical impact: total).
  5. Record last changed materially (score, affected products, status or references).

References

Third-party and government advisories

Technical write-ups (may include proof of concept)

Recent Improper Input Validation vulnerabilities

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