CVE-2026-93222 in Linux
Summary
by MITRE • 09/24/2026
In the Linux kernel, the following vulnerability has been resolved:
signal: avoid shared siginfo namespace rewrites
send_signal_locked() rewrites sender ids for the target namespace. Group sends reuse the same siginfo, so one recipient can affect the next.
Copy the siginfo before changing it.
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Analysis
by VulDB Data Team • 09/24/2026
The Linux kernel contains a critical flaw within its signal handling subsystem that allows for unintended information leakage and potential privilege escalation through improper management of shared signal information structures in user namespaces. This vulnerability specifically affects the send_signal_locked function, which is responsible for delivering signals to processes. When dealing with group sends where multiple threads or processes receive the same signal simultaneously, they share a single siginfo structure. The kernel attempts to rewrite sender identification fields within this shared structure to reflect the correct identity relative to each recipient's user namespace context. However, because the modification occurs in place on a shared data structure rather than creating individual copies for each target process, the state changes made while processing one recipient are immediately visible and potentially disruptive to subsequent recipients sharing that same siginfo block.
This race condition or sequential dependency flaw means that the first process to receive the signal can inadvertently alter the sender identification fields before they are processed by other processes in the group. Since these identifiers determine how permissions and capabilities are evaluated during signal delivery, an attacker who controls one of the recipient threads could manipulate the perceived originator of the signal for subsequent recipients. This undermines the isolation guarantees provided by Linux user namespaces, which are designed to restrict process visibility and privileges within isolated environments. An adversary with access to a container or namespace could exploit this behavior to confuse the kernel's security checks regarding who sent the signal, potentially bypassing restrictions that rely on accurate sender identification for authorization decisions.
From an industry standards perspective, this vulnerability aligns closely with CWE-362, which describes concurrent execution using shared resources without proper synchronization. The core issue is not a classic race condition in the traditional sense of timing-based exploitation but rather a logical flaw where mutable state is incorrectly shared across multiple independent operations that require isolated views of that state. In terms of attack vectors and tactics, this falls under ATT&CK technique T1068, which involves exploitation for privilege escalation. By manipulating signal sender IDs, an attacker might elevate their effective privileges within the namespace or escape containment boundaries if downstream security modules rely on these identifiers to enforce policies. The lack of proper data isolation represents a fundamental breach in the principle of least privilege and secure state management within kernel-space operations.
The operational impact of this flaw is significant for environments relying heavily on containerization and user namespaces, such as cloud-native platforms and multi-tenant hosting services. If exploited successfully, it could allow a malicious process to masquerade as another entity or disrupt the intended delivery mechanisms of critical signals like SIGKILL or SIGTERM, leading to denial of service conditions where processes cannot be properly terminated or managed by system administrators. Furthermore, the confusion in sender identification can lead to incorrect auditing logs and security alerts, hindering incident response efforts. The vulnerability persists until the kernel is patched with a fix that ensures each recipient receives an independent copy of the siginfo structure before any modifications are applied to its contents.
Mitigation strategies primarily involve applying the upstream Linux kernel patch that addresses this issue by modifying send_signal_locked to allocate and populate separate siginfo structures for each target process in a group send operation. This prevents one recipient from affecting the data seen by others. Administrators should ensure their systems are updated with the latest stable kernel versions containing this fix. In environments where immediate patching is not feasible, network segmentation and strict access controls can limit exposure to processes that might attempt to exploit this namespace confusion. Additionally, monitoring for anomalous signal delivery patterns or unexpected changes in process ownership within namespaces may help detect attempted exploitation activities before they result in full compromise.