# CVE-2026-68553: Coturn: Format String Injection via TURN USERNAME/REALM into hiredis Redis Command

> An authenticated user can inject format specifiers into TURN attributes, causing crashes or memory disclosure via Redis command formatting.

- **Severity:** High 7.1 (`CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 19 Aug 2026
- **Updated:** 20 Aug 2026
- **Also known as:** DEBIAN-CVE-2026-68553, GHSA-4g7c-p5wg-j4hp, UBUNTU-CVE-2026-68553

## What is CVE-2026-68553?

CVE-2026-68553 is a high-severity vulnerability in coturn, published on 19 Aug 2026. Any signed-in user can exploit it over the network, with no action from the victim.

### Official description

Coturn is a free open source implementation of TURN and STUN Server. Prior to 4.13.0, an authenticated TURN user can place printf-style format specifiers in the STUN USERNAME or REALM attribute, which passes is_secure_string() validation and is embedded into Redis keys at nine call sites in src/apps/relay/ns_ioalib_engine_impl.c. send_message_to_redis() in src/apps/relay/hiredis_libevent2.c then passes the attacker-controlled key as the format argument to redisAsyncCommand() while supplying only one variadic value, causing hiredis redisvFormatCommand() to read past the va_list. Exploitation can crash the coturn process and terminate active TURN sessions or disclose stack memory into Redis. This issue is fixed in version 4.13.0.

Weakness: CWE-134 (Use of Externally-Controlled Format String)

## Which versions are affected by CVE-2026-68553?


## How do I fix CVE-2026-68553?

Upgrade to a fixed version.

## Is CVE-2026-68553 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-68553 exists.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-68553 and fix it if it is affected.

What it is: CVE-2026-68553 is a high-severity vulnerability in coturn, published on 19 Aug 2026. Any signed-in user can exploit it over the network, with no action from the victim.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-68553 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-2026-68553/ (Markdown: https://insights.sbomify.com/CVE-2026-68553/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-68553
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-68553
- OSV: https://osv.dev/vulnerability/CVE-2026-68553

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-68553/
Summaries are generated and may contain mistakes; the official description above is the record.