CVE-2020-26262 Loopback bypass in Coturn
Attackers can bypass loopback restrictions in Coturn by using specific IP addresses, allowing them to relay packets to internal services.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2020-26262?
CVE-2020-26262 is a high-severity server-side request forgery vulnerability in Fedoraproject Fedora, published on 13 Jan 2021. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
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.
Which versions are affected by CVE-2020-26262?
It affects 2 products.
Products include Coturn Project Coturn, Fedoraproject Fedora.
How do I fix CVE-2020-26262?
Upgrade to a fixed version.
Upgrade, and send outbound requests through an allow-list that blocks internal addresses. More about Server-side request forgery.
Is CVE-2020-26262 being exploited?
There is no known exploitation of CVE-2020-26262 in the wild and no public exploit code.
Other vulnerabilities in Fedoraproject Fedora
- CVE-2018-4056 SQL injection in coTURN
- CVE-2026-43994 Coturn: Stack buffer overflow in decode_oauth_token_gcm()
- CVE-2018-4058 Server-side request forgery in coTURN
- CVE-2026-40613 Coturn: Misaligned Memory Access in coturn STUN Attribute Parser (Remote DoS on ARM64)
- CVE-2026-53450 Coturn: IPv4-mapped 127.0.0.1 bypasses default loopback peer protection
Sources
Also known as CLEANSTART-2023-MJ86716, DEBIAN-CVE-2020-26262, DLA-2522-1, DSA-4829-1, GHSA-6g6j-r9rf-cm7p, MGASA-2021-0087 and 2 more.