CVE-2021-21382: Restund is an open source NAT traversal server. The restund TURN server can be instructed to open a relay to the loopback address range. This allows y...

Description

Restund is an open source NAT traversal server. The restund TURN server can be instructed to open a relay to the loopback address range. This allows you to reach any other service running on localhost which you might consider private. In the configuration that we ship (https://github.com/wireapp/ansible-restund/blob/master/templates/restund.conf.j2#L40-L43) the `status` interface of restund is enabled and is listening on `127.0.0.1`.The `status` interface allows users to issue administrative commands to `restund` like listing open relays or draining connections. It would be possible for an attacker to contact the status interface and issue administrative commands by setting `XOR-PEER-ADDRESS` to `127.0.0.1:{{restund_udp_status_port}}` when opening a TURN channel. We now explicitly disallow relaying to loopback addresses, 'any' addresses, link local addresses, and the broadcast address. As a workaround disable the `status` module in your restund configuration. However there might still be other services running on `127.0.0.0/8` that you do not want to have exposed. The `turn` module can be disabled. Restund will still perform STUN and this might already be enough for initiating calls in your environments. TURN is only used as a last resort when other NAT traversal options do not work. One should also make sure that the TURN server is set up with firewall rules so that it cannot relay to other addresses that you don't want the TURN server to relay to. For example other services in the same VPC where the TURN server is running. Ideally TURN servers should be deployed in an isolated fashion where they can only reach what they need to reach to perform their task of assisting NAT-traversal.

Metrics

CVSS 3.1

9.6/10

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

EPSS Probability

1.47%

70.4th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

Affected Software

Vendor	Product	Versions
Wire	Restund	< 0.4.15

References

https://docs.wire.com/understand/restund.htmlVendor Advisory
https://github.com/coturn/coturn/security/advisories/GHSA-6g6j-r9rf-cm7pNot Applicable
https://github.com/wireapp/ansible-restund/blob/master/templates/restund.conf.j2#L40-L43Exploit, Third Party Advisory
https://github.com/wireapp/restund/pull/7Exploit, Patch, Third Party Advisory
https://github.com/wireapp/restund/security/advisories/GHSA-96j5-w9jq-pv2xExploit, Third Party Advisory
https://talosintelligence.com/vulnerability_reports/TALOS-2018-0732Exploit, Third Party Advisory
https://www.rtcsec.com/post/2021/01/details-about-cve-2020-26262-bypass-of-coturns-default-access-control-protection/#further-concerns-what-elseNot Applicable
https://docs.wire.com/understand/restund.htmlVendor Advisory
https://github.com/coturn/coturn/security/advisories/GHSA-6g6j-r9rf-cm7pNot Applicable
https://github.com/wireapp/ansible-restund/blob/master/templates/restund.conf.j2#L40-L43Exploit, Third Party Advisory
https://github.com/wireapp/restund/pull/7Exploit, Patch, Third Party Advisory
https://github.com/wireapp/restund/security/advisories/GHSA-96j5-w9jq-pv2xExploit, Third Party Advisory
https://talosintelligence.com/vulnerability_reports/TALOS-2018-0732Exploit, Third Party Advisory
https://www.rtcsec.com/post/2021/01/details-about-cve-2020-26262-bypass-of-coturns-default-access-control-protection/#further-concerns-what-elseNot Applicable

Timeline

Published: Jun 11, 2021
Last Modified: Jun 17, 2026
Status: Modified

Frequently Asked Questions

What is CVE-2021-21382?

Restund is an open source NAT traversal server. The restund TURN server can be instructed to open a relay to the loopback address range. This allows you to reach any other service running on localhost which you might consider private. In the configuration that we ship (https://github.com/wireapp/ansible-restund/blob/master/templates/restund.conf.j2#L40-L43) the `status` interface of restund is enabled and is listening on `127.0.0.1`.The `status` interface allows users to issue administrative commands to `restund` like listing open relays or draining connections. It would be possible for an attacker to contact the status interface and issue administrative commands by setting `XOR-PEER-ADDRESS` to `127.0.0.1:{{restund_udp_status_port}}` when opening a TURN channel. We now explicitly disallow relaying to loopback addresses, 'any' addresses, link local addresses, and the broadcast address. As a workaround disable the `status` module in your restund configuration. However there might still be other services running on `127.0.0.0/8` that you do not want to have exposed. The `turn` module can be disabled. Restund will still perform STUN and this might already be enough for initiating calls in your environments. TURN is only used as a last resort when other NAT traversal options do not work. One should also make sure that the TURN server is set up with firewall rules so that it cannot relay to other addresses that you don't want the TURN server to relay to. For example other services in the same VPC where the TURN server is running. Ideally TURN servers should be deployed in an isolated fashion where they can only reach what they need to reach to perform their task of assisting NAT-traversal.

How severe is CVE-2021-21382?

CVE-2021-21382 has a CVSS score of 9.6/10 (CRITICAL severity). The EPSS model estimates a 1.47% probability of exploitation in the next 30 days.

How do I fix CVE-2021-21382?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

How Strix Helps

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