CVE-2020-26262 Loopback bypass in Coturn

2021-01-1318:15:17

CWE-441

CWE-682

GitHub_M

www.cve.org

coturn

loopback bypass

cve-2020-26262

security vulnerability

turn server

stun server

0.0.0.0

127.x.x.x

ipv6

CVSS3

7.2

Attack Vector

NETWORK

Attack Complexity

LOW

Privileges Required

NONE

User Interaction

NONE

Scope

CHANGED

Confidentiality Impact

LOW

Integrity Impact

LOW

Availability Impact

NONE

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

AI Score

6.8

Confidence

High

EPSS

0.002

Percentile

56.7%

JSON

Coturn is free open source implementation of TURN and STUN Server. Coturn before version 4.5.2 by default does not allow peers to connect and relay packets to loopback addresses in the range of 127.x.x.x. However, it was observed that when sending a CONNECT request with the XOR-PEER-ADDRESS value of 0.0.0.0, a successful response was received and subsequently, CONNECTIONBIND also received a successful response. Coturn then is able to relay packets to the loopback interface. Additionally, when coturn is listening on IPv6, which is default, the loopback interface can also be reached by making use of either [::1] or [::] as the peer address. By using the address 0.0.0.0 as the peer address, a malicious user will be able to relay packets to the loopback interface, unless --denied-peer-ip=0.0.0.0 (or similar) has been specified. Since the default configuration implies that loopback peers are not allowed, coturn administrators may choose to not set the denied-peer-ip setting. The issue patched in version 4.5.2. As a workaround the addresses in the address block 0.0.0.0/8, [::1] and [::] should be denied by default unless --allow-loopback-peers has been specified.

CNA Affected

[
  {
    "product": "coturn",
    "vendor": "coturn",
    "versions": [
      {
        "status": "affected",
        "version": "< 4.5.2"
      }
    ]
  }
]