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CVE-2020-26262

Loopback bypass in Coturn

7.2 HighFix available

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.

Attack profile

How easy it is to exploit

Attack vector
Network
Complexity
Low
Privileges needed
None
User interaction
None

What an attacker can affect

Confidentiality
Low
Integrity
Low
Availability
None

Exploit likelihood

1.55%Up 0.3 points since Apr 14, 2021
90%50%10%1%

What each source reports

CVE List Score used 7.2

Loopback bypass in Coturn

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.

Record
CVE-2020-26262
CVSS 3.1
7.2 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:N
Weakness
CWE-441, CWE-682
Updated
2026-11-02
EUVDEUVD-2020-18850 7.2

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.

Record
EUVD-2020-18850
CVSS 3.1
7.2 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:N
Updated
2026-11-03
NVD 7.2

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.

Record
CVE-2020-26262
CVSS 3.1
7.2 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:N
CVSS 2.0
6.4 MediumAV:N/AC:L/Au:N/C:P/I:P/A:N
Weakness
CWE-441, CWE-682
Updated
2026-11-02
OSVALPINE-CVE-2020-26262 7.2

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.

Record
ALPINE-CVE-2020-26262
CVSS 3.1
7.2 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:N
Updated
2026-11-03
OSV 7.2

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.

Record
CVE-2020-26262
CVSS 3.1
7.2 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:N
Updated
2026-11-02
OSVDEBIAN-CVE-2020-26262 7.2

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.

Record
DEBIAN-CVE-2020-26262
CVSS 3.1
7.2 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:N
Updated
2026-11-02
Show 4 moreShow less
OSVUBUNTU-CVE-2020-26262 7.2

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.

Record
UBUNTU-CVE-2020-26262
CVSS 3.1
7.2 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:N
Updated
2026-11-02
OSVMGASA-2021-0087 No score

Updated coturn package fixes a security vulnerability

When sending a CONNECT request with the XOR-PEER-ADDRESS value of 0.0.0.0, a malicious user would be 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 (CVE-2020-26262).

If updating is not possible, the setting --denied-peer-ip=0.0.0.0 can mitigate this issue.

The coturn package has been patched to fix this issue.

Record
MGASA-2021-0087
Updated
2026-11-02
OSVopenSUSE-SU-2024:10696-1 No score

coturn-4.5.2-2.2 on GA media

These are all security issues fixed in the coturn-4.5.2-2.2 package on the GA media of openSUSE Tumbleweed.

Record
openSUSE-SU-2024:10696-1
Updated
2026-11-02
OSVUSN-4690-1 No score

coturn vulnerability

It was discovered that coTURN allowed peers to connect and relay packets to loopback addresses in the range of 127.x.x.x. A malicious user could use this vulnerability to insert packages into the loopback interface.

Record
USN-4690-1
Updated
2026-11-02

Affected products

Affected packages

Affected packages
PackageAffectedFixed
coturn
Alpine:v3.13
before 4.5.2-r0
4.5.2-r0
coturn
Alpine:v3.14
before 4.5.2-r0
4.5.2-r0
coturn
Alpine:v3.15
before 4.5.2-r0
4.5.2-r0
coturn
Alpine:v3.16
before 4.5.2-r0
4.5.2-r0
coturn
Alpine:v3.17
before 4.5.2-r0
4.5.2-r0
coturn
Alpine:v3.18
before 4.5.2-r0
4.5.2-r0
coturn
Alpine:v3.19
before 4.5.2-r0
4.5.2-r0
coturn
Alpine:v3.20
before 4.5.2-r0
4.5.2-r0
coturn
Alpine:v3.21
before 4.5.2-r0
4.5.2-r0
coturn
Alpine:v3.22
before 4.5.2-r0
4.5.2-r0
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Affected packages
PackageAffectedFixed
coturn
Alpine:v3.23
before 4.5.2-r0
4.5.2-r0
coturn
Alpine:v3.24
before 4.5.2-r0
4.5.2-r0
coturn
Debian:12
before 4.5.2-1
4.5.2-1
coturn
Debian:13
before 4.5.2-1
4.5.2-1
coturn
Debian:14
before 4.5.2-1
4.5.2-1
coturn
Debian:9
before 4.5.0.5-1+deb9u3, plus listed versions
4.5.0.5-14.5.0.5-1+deb9u14.5.0.5-1+deb9u2
4.5.0.5-1+deb9u3
coturn
Debian:10
before 4.5.1.1-1.1+deb10u2, plus listed versions
4.5.1.1-1.14.5.1.1-1.1+deb10u1
4.5.1.1-1.1+deb10u2
coturn
Mageia:7
before 4.5.2-1.4.mga7
4.5.2-1.4.mga7
coturn
Ubuntu:16.04:LTS
before 4.5.0.3-1ubuntu0.4, plus listed versions
4.4.5.4-24.5.0.2-34.5.0.3-14.5.0.3-1build14.5.0.3-1ubuntu0.24.5.0.3-1ubuntu0.3
4.5.0.3-1ubuntu0.4
coturn
Ubuntu:18.04:LTS
before 4.5.0.7-1ubuntu2.18.04.3, plus listed versions
4.5.0.6-1ubuntu24.5.0.7-1ubuntu14.5.0.7-1ubuntu24.5.0.7-1ubuntu2.18.04.14.5.0.7-1ubuntu2.18.04.2
4.5.0.7-1ubuntu2.18.04.3
coturn
Ubuntu:20.04:LTS
before 4.5.1.1-1.1ubuntu0.20.04.2, plus listed versions
4.5.1.1-1.1build14.5.1.1-1.1build24.5.1.1-1.1ubuntu0.20.04.1
4.5.1.1-1.1ubuntu0.20.04.2
coturn
openSUSE:Tumbleweed
From an advisory covering 3 CVEs
before 4.5.2-2.2
4.5.2-2.2

History

History
RecordedChangedSources
affected, facts
affected, aliases, referencesOSV
aliasesEUVD
first indexedCVE List, NVD, OSV

Dates are when Every CVE recorded each change. Upstream dates may differ.

In short

CVE-2020-26262 is a high vulnerability (CVSS 7.2) in Coturn, published January 11, 2021. No source lists public exploit code. EPSS puts the chance of exploitation in the next 30 days at 1.55%, the 75th percentile. Fixed in coturn 4.5.2-r0.

References

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