CVE-2021-21382

CVE-2021-21382 is a high-severity vulnerability in Wire Restund with a CVSS 3.x base score of 8.6. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-862.

Key facts

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.

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 3.x base score of 8.6, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity none, and availability none.
Is CVE-2021-21382 being actively exploited?
It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (73rd percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-21382?
CVE-2021-21382 affects Wire Restund. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2021-21382?
Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.
When was CVE-2021-21382 published?
CVE-2021-21382 was published on 2021-06-11 and last updated on 2026-06-17.

References

Affected products (1)

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