CVE-2021-46929 is a use-after-free vulnerability in the Linux kernel's SCTP (Stream Control Transmission Protocol) implementation. The issue arises in the sctp_sock_dump() function, where an endpoint (ep) is freed prematurely after being accessed via asoc->base.sk but before the lock_sock(sk) call. This leads to a use-after-free condition, which can cause kernel crashes or potentially allow an attacker to execute arbitrary code in kernel space. The root cause is that the endpoint is freed too early, and the patch delays freeing the endpoint by using call_rcu(), a Read-Copy-Update mechanism that defers freeing until it is safe. This ensures the endpoint remains alive while being accessed and locked, preventing the use-after-free. The fix moves the sock_put and endpoint free operations into sctp_endpoint_destroy_rcu(), which is called after the RCU grace period. The vulnerability is triggered when an SCTP association is peeled off, and the old socket is freed prematurely. The patch also adds checks to skip processing if the endpoint is no longer alive. This vulnerability affects Linux kernel versions containing the specified commit (d25adbeb0cdb860fb39e09cdd025e9cfc954c5ab) and earlier versions without the patch. No known exploits are reported in the wild yet. The vulnerability is technical and specific to SCTP, a transport layer protocol used in some telecom and networking environments. Exploitation requires triggering SCTP socket operations that cause the use-after-free condition.

For European organizations, the impact depends on their use of Linux systems running vulnerable kernel versions and whether they utilize SCTP for networking. SCTP is commonly used in telecom infrastructure, signaling, and some specialized applications. Organizations in telecom, critical infrastructure, and data centers using Linux with SCTP enabled could face kernel crashes leading to denial of service or potentially privilege escalation if an attacker crafts malicious SCTP packets. This could disrupt services, cause outages, or allow attackers to gain kernel-level control. Given the Linux kernel's widespread use across servers and embedded devices in Europe, the vulnerability could affect a broad range of systems if unpatched. However, exploitation complexity and the need for SCTP usage limit the attack surface. Still, critical infrastructure operators and telecom providers should prioritize patching to avoid service disruptions and security breaches.

European organizations should apply the Linux kernel patch that fixes CVE-2021-46929 as soon as possible. Specifically, they should update to kernel versions that include the call_rcu() based fix in the SCTP subsystem. For environments where immediate patching is challenging, mitigating controls include disabling SCTP if not required, or restricting SCTP traffic via network firewalls and segmentation to limit exposure. Monitoring kernel logs for unusual SCTP-related errors or crashes can help detect exploitation attempts. Organizations should also audit their Linux systems to identify vulnerable kernel versions and SCTP usage. For telecom operators, coordination with vendors and infrastructure providers to deploy patched kernel versions is critical. Additionally, employing kernel hardening techniques and runtime protections can reduce exploitation risk.