Coturn is a free open source implementation of TURN and STUN Server. Coturn is commonly configured to block loopback and internal ranges using denied-peer-ip and/or default loopback restrictions. CVE-2020-26262 addressed bypasses involving 0.0.0.0, [::1] and [::], but IPv4-mapped IPv6 is not covered. When sending a CreatePermission or ChannelBind request with the XOR-PEER-ADDRESS value of ::ffff:127.0.0.1, a successful response is received, even though 127.0.0.0/8 is blocked via denied-peer-ip. The root cause is that, prior to the updated fix implemented in version 4.9.0, three functions in src/client/ns_turn_ioaddr.c do not check IN6_IS_ADDR_V4MAPPED. ioa_addr_is_loopback() checks 127.x.x.x (AF_INET) and ::1 (AF_INET6), but not ::ffff:127.0.0.1. ioa_addr_is_zero() checks 0.0.0.0 and ::, but not ::ffff:0.0.0.0. addr_less_eq() used by ioa_addr_in_range() for denied-peer-ip matching: when the range is AF_INET and the peer is AF_INET6, the comparison returns 0 without extracting the embedded IPv4. Version 4.9.0 contains an updated fix to address the bypass of the fix for CVE-2020-26262.
Weakness
The product does not restrict or incorrectly restricts access to a resource from an unauthorized actor.
Affected Software
| Name | Vendor | Start Version | End Version |
|---|---|---|---|
| Coturn | Coturn_project | * | 4.9.0 (excluding) |
Extended Description
Access control involves the use of several protection mechanisms such as:
When any mechanism is not applied or otherwise fails, attackers can compromise the security of the product by gaining privileges, reading sensitive information, executing commands, evading detection, etc. There are two distinct behaviors that can introduce access control weaknesses:
Potential Mitigations
- Compartmentalize the system to have “safe” areas where trust boundaries can be unambiguously drawn. Do not allow sensitive data to go outside of the trust boundary and always be careful when interfacing with a compartment outside of the safe area.
- Ensure that appropriate compartmentalization is built into the system design, and the compartmentalization allows for and reinforces privilege separation functionality. Architects and designers should rely on the principle of least privilege to decide the appropriate time to use privileges and the time to drop privileges.
Related Attack Patterns
- https://cwe.mitre.org/data/definitions/19.html
- https://cwe.mitre.org/data/definitions/441.html
- https://cwe.mitre.org/data/definitions/478.html
- https://cwe.mitre.org/data/definitions/479.html
- https://cwe.mitre.org/data/definitions/502.html
- https://cwe.mitre.org/data/definitions/503.html
- https://cwe.mitre.org/data/definitions/536.html
- https://cwe.mitre.org/data/definitions/546.html
- https://cwe.mitre.org/data/definitions/550.html
- https://cwe.mitre.org/data/definitions/551.html
- https://cwe.mitre.org/data/definitions/552.html
- https://cwe.mitre.org/data/definitions/556.html
- https://cwe.mitre.org/data/definitions/558.html
- https://cwe.mitre.org/data/definitions/562.html
- https://cwe.mitre.org/data/definitions/563.html
- https://cwe.mitre.org/data/definitions/564.html
- https://cwe.mitre.org/data/definitions/578.html
References
- https://github.com/coturn/coturn/commit/b80eb898ba26552600770162c26a8ae7f3661b0b
- https://github.com/coturn/coturn/security/advisories/GHSA-6g6j-r9rf-cm7p
- https://github.com/coturn/coturn/security/advisories/GHSA-j8mm-mpf8-gvjg
- https://github.com/coturn/coturn/security/advisories/GHSA-6g6j-r9rf-cm7p
- https://github.com/coturn/coturn/security/advisories/GHSA-j8mm-mpf8-gvjg