Coturn up to 4.9.x OAuth Access Token decode_oauth_token_gcm buffer overflow

Summaryinfo

A vulnerability was found in Coturn up to 4.9.x and classified as critical. Impacted is the function decode_oauth_token_gcm of the component OAuth Access Token Handler. Such manipulation leads to buffer overflow. This vulnerability is listed as CVE-2026-43994. The attack may be performed from remote. There is no available exploit. It is suggested to upgrade the affected component.

Detailsinfo

A vulnerability, which was classified as critical, has been found in Coturn up to 4.9.x. Affected by this issue is the function decode_oauth_token_gcm of the component OAuth Access Token Handler. The manipulation with an unknown input leads to a buffer overflow vulnerability. Using CWE to declare the problem leads to CWE-120. The product copies an input buffer to an output buffer without verifying that the size of the input buffer is less than the size of the output buffer, leading to a buffer overflow. Impacted is confidentiality, integrity, and availability. CVE summarizes:

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.

The advisory is available at github.com. This vulnerability is handled as CVE-2026-43994 since 05/04/2026. The exploitation is known to be difficult. The attack may be launched remotely. No form of authentication is required for exploitation. Technical details are known, but there is no available exploit.

Upgrading to version 4.10.0 eliminates this vulnerability. The upgrade is hosted for download at github.com.

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Productinfo

Name

• Coturn

Version

• 4.0
• 4.1
• 4.2
• 4.3
• 4.4
• 4.5
• 4.6
• 4.7
• 4.8
• 4.9

Website

• Product: https://github.com/coturn/coturn/

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