Description
Coturn is a free open source implementation of TURN and STUN Server. Prior to 4.13.0, coturn rejects loopback peers by default unless allow-loopback-peers is enabled, but the default loopback guard can be bypassed by using the IPv4-mapped IPv6 peer address ::ffff:127.0.0.1 in a TURN XOR-PEER-ADDRESS attribute. ioa_addr_is_loopback checks for the literal IPv6 loopback shape before IPv4-mapped IPv6 handling, so good_peer_addr does not apply the default loopback rejection and an authenticated TURN client can expose services bound only to localhost on the coturn host through TURN relay traffic. This issue is fixed in version 4.13.0.
Published: 2026-07-10
Score: 7.4 High
EPSS: < 1% Very Low
KEV: No
Impact: n/a
Action: n/a
AI Analysis

Impact

Coturn implements TURN/STUN services and by default rejects loopback peers. Prior to version 4.13.0, an authenticated client can send a TURN packet that contains the IPv4‑mapped IPv6 address ::ffff:127.0.0.1 in the XOR-PEER-ADDRESS attribute. This causes the server to treat the loopback address as an external peer, bypassing the default protection and allowing traffic to be relayed to processes bound only to 127.0.0.1. The flaw is an access‑control failure (CWE‑289) and a failure to handle IPv4‑mapped addresses correctly (CWE‑918).

Affected Systems

coturn:coturn versions earlier than 4.13.0 are vulnerable. The default configuration disables allow-loopback-peers, so any installation that has not been updated to 4.13.0 or newer is at risk.

Risk and Exploitability

The CVSS score of 7.4 indicates high severity, while the EPSS of <1% suggests a low to moderate exploitation probability. The vulnerability is not listed in the CISA KEV catalog. An attacker must first authenticate to the TURN server; once authenticated, they can craft packets to relay traffic to the localhost. No additional local privileges on the coturn host are required, and the attack classifies as a remote network exploit via the TURN protocol.

Generated by OpenCVE AI on July 29, 2026 at 10:25 UTC.

Remediation

No vendor fix or workaround currently provided.

OpenCVE Recommended Actions

  • Upgrade coturn to version 4.13.0 or later to apply the fix that restores loopback peer rejection.
  • If an upgrade is not immediately feasible, restrict TURN client authentication to trusted networks and enforce strict ACLs so that only authorized peers can connect.
  • Lock down any services bound to 127.0.0.1 by configuring them to listen only on the loopback interface and, if possible, block TURN‑relay traffic to loopback addresses with firewall rules.

Generated by OpenCVE AI on July 29, 2026 at 10:25 UTC.

Tracking

Sign in to view the affected projects.

Advisories

No advisories yet.

History

Sat, 11 Jul 2026 00:15:00 +0000

Type Values Removed Values Added
Weaknesses CWE-289
References
Metrics threat_severity

None

 threat_severity

Important

Fri, 10 Jul 2026 19:45:00 +0000

Type Values Removed Values Added
First Time appeared Coturn
Coturn coturn
Vendors & Products Coturn
Coturn coturn

Fri, 10 Jul 2026 19:30:00 +0000

Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'no', 'Exploitation': 'poc', 'Technical Impact': 'partial'}, 'version': '2.0.3'}

Fri, 10 Jul 2026 18:30:00 +0000

Type Values Removed Values Added
Description Coturn is a free open source implementation of TURN and STUN Server. Prior to 4.13.0, coturn rejects loopback peers by default unless allow-loopback-peers is enabled, but the default loopback guard can be bypassed by using the IPv4-mapped IPv6 peer address ::ffff:127.0.0.1 in a TURN XOR-PEER-ADDRESS attribute. ioa_addr_is_loopback checks for the literal IPv6 loopback shape before IPv4-mapped IPv6 handling, so good_peer_addr does not apply the default loopback rejection and an authenticated TURN client can expose services bound only to localhost on the coturn host through TURN relay traffic. This issue is fixed in version 4.13.0.
Title Coturn: IPv4-mapped 127.0.0.1 bypasses default loopback peer protection
Weaknesses CWE-918
References
Metrics cvssV3_1

{'score': 7.4, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:L/I:L/A:L'}

Subscriptions

Coturn Coturn
cve-icon MITRE

Status: PUBLISHED

Assigner: GitHub_M

Published:

Updated: 2026-07-10T19:03:44.107Z

Reserved: 2026-06-09T16:31:21.494Z

Link: CVE-2026-53450

cve-icon Vulnrichment

Updated: 2026-07-10T19:03:38.177Z

cve-icon NVD

No data.

cve-icon Redhat

Severity : Important

Publid Date: 2026-07-10T18:05:06Z

Links: CVE-2026-53450 - Bugzilla

cve-icon OpenCVE Enrichment

Updated: 2026-07-29T10:30:05Z

Weaknesses
  • CWE-289

    Authentication Bypass by Alternate Name

  • CWE-918

    Server-Side Request Forgery (SSRF)