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Fencer Vulns
high 7.2

CVE-2020-26262 json

Loopback bypass in Coturn

published 2021-01-13 5 y ago modified 2026-06-17 4 mo ago also EUVD-2020-18850

cvss
7.2
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
1.5%
EPSS 1.5% chance of exploitation in 30 days, percentile 75%
public exploits
0
none known

Summary

Coturn is free open source implementation of TURN and STUN Server. Coturn before version 4.5.2 by default does not allow peers to connect and relay packets to loopback addresses in the range of `127.x.x.x`. However, it was observed that when sending a `CONNECT` request with the `XOR-PEER-ADDRESS` value of `0.0.0.0`, a successful response was received and subsequently, `CONNECTIONBIND` also received a successful response. Coturn then is able to relay packets to the loopback interface. Additionally, when coturn is listening on IPv6, which is default, the loopback interface can also be reached by making use of either `[::1]` or `[::]` as the peer address. By using the address `0.0.0.0` as the peer address, a malicious user will be able to relay packets to the loopback interface, unless `--denied-peer-ip=0.0.0.0` (or similar) has been specified. Since the default configuration implies that loopback peers are not allowed, coturn administrators may choose to not set the `denied-peer-ip` setting. The issue patched in version 4.5.2. As a workaround the addresses in the address block `0.0.0.0/8`, `[::1]` and `[::]` should be denied by default unless `--allow-loopback-peers` has been specified.

Patch / fix

  • coturn_project coturn 4.5.2
  • coturn Debian 14, Debian 13, Debian 12 4.5.2-1

debian advisories DEBIAN-CVE-2020-26262

  • coturn Ubuntu 16.04 LTS 4.5.0.3-1ubuntu0.4
  • coturn Ubuntu 18.04 LTS 4.5.0.7-1ubuntu2.18.04.3
  • coturn Ubuntu 20.04 LTS 4.5.1.1-1.1ubuntu0.20.04.2

ubuntu advisories UBUNTU-CVE-2020-26262

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • coturn openSUSE Tumbleweed 4.5.2-2.2

opensuse advisories openSUSE-SU-2024:10696-1

  • coturn Alpine 3.24, Alpine 3.23, Alpine 3.22 +9 more 4.5.2-r0

alpine advisories ALPINE-CVE-2020-26262

Alpine secdb © Alpine Linux, from https://secdb.alpinelinux.org via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • coturn Arch Linux 4.5.2-1

arch linux advisories AVG-1430

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2020-26262 updated cvss 7.4

coturn: Loopback access control bypass

  • Red Hat All currently supported Red Hat products
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

Exploit prediction

1.55% chance of exploitation in the next 30 days, higher than 75% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

  • github.com https://github.com/coturn/coturn/security/advisories/GHSA-6g6j-r9rf-cm7p referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
CNA 3.1 7.2 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:N
NVD 3.1 7.2 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:N
NVD 2.0 6.4 AV:N/AC:L/Au:N/C:P/I:P/A:N

Affected products

  • coturn coturn

Classification

Weakness
  • CWE-441 Unintended Proxy or Intermediary
  • CWE-682 Incorrect Calculation

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.