Bug 2490587 (CVE-2026-43994)

Summary: CVE-2026-43994 coturn: Coturn: Arbitrary Code Execution due to stack buffer overflow in OAuth token processing
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security <prodsec-ir-bot>
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Version: unspecifiedKeywords: Security
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OS: Linux   
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A flaw was found in Coturn, an open-source TURN and STUN server. A remote attacker can exploit a stack buffer overflow vulnerability by providing a specially crafted OAuth access token when the server is configured to use `--oauth` mode. This could lead to arbitrary code execution (RCE), allowing the attacker to run malicious code on the affected system. The vulnerability exists due to improper handling of the `nonce_len` field, which allows writing data beyond a 256-byte stack buffer.
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Description OSIDB Bzimport 2026-06-18 21:01:24 UTC 
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.