# CVE-2026-27624: Coturn: IPv4-mapped IPv6 (::ffff:0:0/96) bypasses denied-peer-ip ACL

> Attackers can bypass denied-peer-ip ACLs in Coturn by using IPv4-mapped IPv6 addresses, allowing connections to blocked internal ranges.

- **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:** 25 Feb 2026
- **Updated:** 25 Feb 2026
- **Also known as:** DEBIAN-CVE-2026-27624, MGASA-2026-0051, UBUNTU-CVE-2026-27624

## What is CVE-2026-27624?

CVE-2026-27624 is a high-severity vulnerability in coturn, published on 25 Feb 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

Coturn is a free open source implementation of TURN and STUN Server. Coturn is commonly configured to block loopback and internal ranges using "denied-peer-ip" and/or default loopback restrictions. CVE-2020-26262 addressed bypasses involving "0.0.0.0", "[::1]" and "[::]", but IPv4-mapped IPv6 is not covered. When sending a "CreatePermission" or "ChannelBind" request with the "XOR-PEER-ADDRESS" value of "::ffff:127.0.0.1", a successful response is received, even though "127.0.0.0/8" is blocked via "denied-peer-ip". The root cause is that, prior to the updated fix implemented in version 4.9.0, three functions in "src/client/ns_turn_ioaddr.c" do not check "IN6_IS_ADDR_V4MAPPED". "ioa_addr_is_loopback()" checks "127.x.x.x" (AF_INET) and "::1" (AF_INET6), but not "::ffff:127.0.0.1." "ioa_addr_is_zero()" checks "0.0.0.0" and "::", but not "::ffff:0.0.0.0." "addr_less_eq()" used by "ioa_addr_in_range()" for "denied-peer-ip" matching: when the range is AF_INET and the peer is AF_INET6, the comparison returns 0 without extracting the embedded IPv4. Version 4.9.0 contains an updated fix to address the bypass of the fix for CVE-2020-26262.

Weakness: CWE-441 (Unintended Proxy or Intermediary), CWE-284 (Improper Access Control)

## Which versions are affected by CVE-2026-27624?

It affects 1 product.


Products: Coturn Project Coturn.

## How do I fix CVE-2026-27624?

Upgrade to a fixed version.

## Is CVE-2026-27624 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-27624 exists.

## Other vulnerabilities in coturn

- [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-2026-27624 and fix it if it is affected.

What it is: CVE-2026-27624 is a high-severity vulnerability in coturn, published on 25 Feb 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-27624 exists.

Affected product: coturn. 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-2026-27624/ (Markdown: https://insights.sbomify.com/CVE-2026-27624/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-27624
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-27624
- OSV: https://osv.dev/vulnerability/CVE-2026-27624

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-27624/
Summaries are generated and may contain mistakes; the official description above is the record.