CVE-2020-26262

Loopback bypass in Coturn

HIGH

7.2

CVSS Score

Published: January 13, 2021 at 06:15 PM UTC

Updated: June 17, 2026 at 03:07 AM UTC

2 products affected across 2 vendorsFedoraCoturn

Using coturn by coturn?

Get instant alerts when new vulnerabilities affect coturn - before attackers find them.

Real-time alertsTrack your software stackFree plan available

Start Free Sign In

Severity

HIGH7.2

Exploit prediction

EPSS 2%

Description

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.