Vulnerability CVE-2020-26262


Published: 2021-01-13

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.

See advisories in our WLB2 database:
Topic
Author
Date
High
Coturn 4.5.1.x Access Control Bypass
Sandro Gauci
11.01.2021

Type:

CWE-682

(Incorrect Calculation)

CVSS2 => (AV:N/AC:L/Au:N/C:P/I:P/A:N)

CVSS Base Score
Impact Subscore
Exploitability Subscore
6.4/10
4.9/10
10/10
Exploit range
Attack complexity
Authentication
Remote
Low
No required
Confidentiality impact
Integrity impact
Availability impact
Partial
Partial
None
Affected software
Coturn project -> Coturn 

 References:
https://github.com/coturn/coturn/blob/57180ab60afcaeb13537e69ae8cb8aefd8f3f546/ChangeLog#L48
https://github.com/coturn/coturn/commit/abfe1fd08d78baa0947d17dac0f7411c3d948e4d
https://github.com/coturn/coturn/security/advisories/GHSA-6g6j-r9rf-cm7p
https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/G54UIUFTEC6RLPOISMB6FUW7456SBZC4/
https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/M4CJOPAQT43MYAFU3UROGLEXN3Z6RS4H/

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