# 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.

- **Severity:** High 7.2 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 13 Jan 2021
- **Updated:** 4 Aug 2024
- **Also known as:** CLEANSTART-2023-MJ86716, DEBIAN-CVE-2020-26262, DLA-2522-1, DSA-4829-1, GHSA-6g6j-r9rf-cm7p, MGASA-2021-0087, UBUNTU-CVE-2020-26262, USN-4690-1

## 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.

Weakness: CWE-682 (Incorrect Calculation), CWE-441 (Unintended Proxy or Intermediary)

## Which versions are affected by CVE-2020-26262?

It affects 2 products.


Products: Coturn Project Coturn, Fedoraproject Fedora.

## How do I fix CVE-2020-26262?

Upgrade to a fixed version.

## 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](https://insights.sbomify.com/CVE-2018-4056/): SQL injection in coTURN (critical 9.1)
- [CVE-2026-43994](https://insights.sbomify.com/CVE-2026-43994/): Coturn: Stack buffer overflow in decode_oauth_token_gcm() (high 8.1)
- [CVE-2018-4058](https://insights.sbomify.com/CVE-2018-4058/): Server-side request forgery in coTURN (high 7.7)
- [CVE-2026-40613](https://insights.sbomify.com/CVE-2026-40613/): Coturn: Misaligned Memory Access in coturn STUN Attribute Parser (Remote DoS on ARM64) (high 7.5)
- [CVE-2026-53450](https://insights.sbomify.com/CVE-2026-53450/): Coturn: IPv4-mapped 127.0.0.1 bypasses default loopback peer protection (high 7.4)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2020-26262 and fix it if it is affected.

What it is: 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.
Exploitation: There is no known exploitation of CVE-2020-26262 in the wild and no public exploit code.

Affected product: Fedoraproject Fedora. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2020-26262/ (Markdown: https://insights.sbomify.com/CVE-2020-26262/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2020-26262
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2020-26262
- OSV: https://osv.dev/vulnerability/CVE-2020-26262

---
From sbomify Insights: https://insights.sbomify.com/CVE-2020-26262/
Summaries are generated and may contain mistakes; the official description above is the record.