Coturn prior 4.13.0 Redis Integration hiredis_libevent2.c redisvFormatCommand format string

Summaryinfo

A vulnerability classified as critical has been found in Coturn prior 4.13.0. Affected by this issue is the function redisvFormatCommand of the file src/apps/relay/hiredis_libevent2.c of the component Redis Integration. This manipulation causes format string. This vulnerability is tracked as CVE-2026-68553. The attack is possible to be carried out remotely. No exploit exists.

Detailsinfo

A vulnerability classified as critical was found in Coturn prior 4.13.0. Affected by this vulnerability is the function redisvFormatCommand of the file src/apps/relay/hiredis_libevent2.c of the component Redis Integration. The manipulation with an unknown input leads to a format string vulnerability. The CWE definition for the vulnerability is CWE-134. The product uses a function that accepts a format string as an argument, but the format string originates from an external source. As an impact it is known to affect confidentiality, integrity, and availability. The summary by CVE is:

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.

It is possible to read the advisory at github.com. This vulnerability is known as CVE-2026-68553 since 07/30/2026. The exploitation appears to be easy. The attack can be launched remotely. Technical details of the vulnerability are known, but there is no available exploit. The pricing for an exploit might be around USD $0-$5k at the moment (estimation calculated on 08/19/2026).

There is no information about possible countermeasures known. It may be suggested to replace the affected object with an alternative product.

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Productinfo

Name

• Coturn

Version

• <4.13.0

Website

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

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