# CVE-2026-43994: Coturn: Stack buffer overflow in decode_oauth_token_gcm()

> Attacker can achieve remote code execution via stack buffer overflow in Coturn's OAuth token decoding when OAuth mode is enabled.

- **Severity:** High 8.1 (`CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 18 Jun 2026
- **Updated:** 22 Jun 2026
- **Also known as:** DEBIAN-CVE-2026-43994, GHSA-74pg-rfh2-5qw5, UBUNTU-CVE-2026-43994

## What is CVE-2026-43994?

CVE-2026-43994 is a high-severity memory corruption vulnerability in coturn, published on 18 Jun 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. Versions prior to 4.10.0 contain a stack buffer overflow in decode_oauth_token_gcm(). A uint16_t nonce_len field read from an attacker-supplied OAuth access token (0-65535) is passed directly to memcpy() as the copy length into a 256-byte stack buffer (oauth_encrypted_block.nonce[256]) without bounds checking. The overflow occurs before AES-GCM authentication is verified, the attacker does not need to know the OAuth key or produce a valid AES-GCM token. Up to 735 bytes of attacker-controlled data are written past the buffer, may corrupt adjacent stack data, including control-flow data depending on compiler, ABI, and mitigations. Requires --oauth mode (non-default). This may provide a plausible RCE primitive depending on exploit mitigations; because coturn is widely deployed for WebRTC TURN/STUN and --oauth is commonly recommended, impact can be broad. This issue has been fixed in version 4.10.0.

Weakness: CWE-120 (Buffer Copy without Checking Size of Input)

## Which versions are affected by CVE-2026-43994?

It affects 1 product.


Products: Coturn Project Coturn.

## How do I fix CVE-2026-43994?

Upgrade to a fixed version.

## Is CVE-2026-43994 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-43994 exists.

## Other vulnerabilities in coturn

- [CVE-2018-4056](https://insights.sbomify.com/CVE-2018-4056/): SQL injection in coTURN (critical 9.1)
- [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)
- [CVE-2026-53448](https://insights.sbomify.com/CVE-2026-53448/): Coturn: SQL Injection in HTTPS Admin Panel Delete Operations (high 7.2)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-43994 and fix it if it is affected.

What it is: CVE-2026-43994 is a high-severity memory corruption vulnerability in coturn, published on 18 Jun 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-2026-43994 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-2026-43994/ (Markdown: https://insights.sbomify.com/CVE-2026-43994/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-43994
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-43994
- OSV: https://osv.dev/vulnerability/CVE-2026-43994

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-43994/
Summaries are generated and may contain mistakes; the official description above is the record.