CVE-2026-35091

A flaw was found in Corosync. A remote unauthenticated attacker can exploit a wrong return value vulnerability in the Corosync membership commit token sanity check by sending a specially crafted User Datagram Protocol (UDP) packet. This can lead to an out-of-bounds read, causing a denial of service (DoS) and potentially disclosing limited memory contents

This vulnerability has a Moderate impact on Red Hat products. A flaw in Corosync's membership commit token sanity check, when running in the totemudp/totemudpu mode, allows a remote unauthenticated attacker to send a crafted UDP packet. This can lead to an out-of-bounds read, resulting in a denial of service and potential limited memory content disclosure. This issue affects Corosync only when configured to use the legacy totemudp or totemudpu transport modes with unencrypted communication.

These modes are not the default in modern Corosync versions. The default transport is knet, which supports encryption and is the standard configuration in RHEL.Additionally, totemudp and totemudpu are unsupported in RHEL, and their use requires explicit manual configuration.

The CVSS score(s) listed for this vulnerability do not reflect the associated product's status, and are included for informational purposes to better understand the severity of this vulnerability.

Systems using totemudp or totemudpu should migrate to the supported knet transport and enable encryption.

Disabling the Corosync service is a valid workaround if clustering is not required, but for active clusters, enabling encryption via knet is the preferred and recommended approach.