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CoturnApplication · Coturn Project

CVE-2026-43994

CRITICAL · 9.8 CVSS v3.1 Published 2026-06-18
Fix available
A fix is available. Upgrade to 4.10.0 or later.
See remediation →
100/100
Remediation priority · Urgent
Public exploit Remotely reachable No privileges Zero-click

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
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.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

Coturn versions before 4.10.0 contain a stack buffer overflow in the decode_oauth_token_gcm() function where a uint16_t nonce_len field (0-65535) from an attacker-supplied OAuth token is used directly as the length parameter to memcpy() into a fixed 256-byte stack buffer (oauth_encrypted_block.nonce[256]) without any bounds validation. The overflow occurs before AES-GCM authentication is verified, allowing unauthenticated attackers to write up to 735 bytes of attacker-controlled data past the buffer boundary, potentially corrupting adjacent stack variables including control-flow data.

MitigationUpgrade coturn to version 4.10.0 or later which contains the fix for proper bounds checking before the memcpy operation. Until upgrade is complete, consider disabling --oauth mode if operationally feasible, though this is non-default so may not be actively used.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
CoturnApplication
Affected:< 4.10.0

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Identify coturn version
    Run 'turnserver --version' or check the installed package version using your system's package manager (e.g., dpkg -l coturn, rpm -qi coturn)
    Affected if The installed version is less than 4.10.0 (e.g., 4.9.0, 4.8.0, etc.)
  2. Locate coturn configuration file
    Common locations include /etc/turnserver.conf, /etc/turn/turnserver.conf, or consult your deployment documentation for the active configuration path
    Affected if Configuration file exists and OAuth-related settings are present
  3. Verify OAuth mode is enabled
    Search the configuration file for 'oauth' keyword. Look for lines containing 'oauth', 'oauth-token', or similar OAuth-related directives. The vulnerability is only exploitable when OAuth token processing is active
    Affected if OAuth mode is explicitly enabled in the configuration (e.g., presence of oauth, oauth-token, or similar directives) or the server is configured to process OAuth tokens from incoming requests
  4. Check for OAuth-related runtime parameters
    Run 'turnserver --help' or review startup scripts for any --oauth flags or environment variables that enable OAuth processing at runtime
    Affected if OAuth processing is active at runtime via command-line flags or environment configuration

You are affected if coturn version is below 4.10.0 AND OAuth mode is enabled (the attack requires both conditions to be true).

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Upgrade available Upgrade to 4.10.0 or later
Fixed in 4.10.0
Interim mitigation

Upgrade coturn to version 4.10.0 or later which contains the fix for proper bounds checking before the memcpy operation. Until upgrade is complete, consider disabling --oauth mode if operationally feasible, though this is non-default so may not be actively used.

Recommended fix High confidence

4.10.0

  1. 1. Identify the current Coturn version by running `turnadmin --version` or checking the package manager
  2. 2. Download Coturn version 4.10.0 or later from the official GitHub repository (github.com/coturn/coturn) or update via your package manager
  3. 3. Backup your current Coturn configuration files (usually in /etc/ or /usr/local/etc/)
  4. 4. Install the upgraded Coturn package or compile from source
  5. 5. Restore your configuration and verify the service starts successfully
  6. 6. Confirm the version has been updated by running `turnadmin --version`

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Coturn Scoped from the published advisory
  • Consultation2.0 h
  • Implementation4.0 h
  • Testing3.0 h
  • Review / QA2.0 h
11.0 hours of engineering $1,930
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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2026-43994 in production — separate from our analysis above.

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What this is

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What belongs here
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  • Version or environment caveats, and links to real fixes
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