CVE-2026-121398 in FreeRDP
Summary
by MITRE • 11/03/2026
FreeRDP before 3.32.2 contains a cross-thread use-after-free vulnerability in the freerdp-proxy dyn-channel-dump module during session teardown. A malicious RDP target can send dynamic channel data while the front client disconnects, letting the client thread read freed ChannelData and crash the proxy process.
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Analysis
by VulDB Data Team • 11/03/2026
The identified vulnerability resides within the FreeRDP software suite, specifically affecting versions prior to 3.32.2 in the dyn-channel-dump module of the freerdp-proxy component. This security flaw is classified as a cross-thread use-after-free condition, which represents a critical memory management error where memory allocated for an object is freed while it is still being accessed by another thread. In this specific context, the vulnerability emerges during the session teardown phase when the proxy process attempts to clean up resources associated with a disconnected Remote Desktop Protocol client. The core technical flaw involves a race condition between the main client disconnect handling logic and the background processing of dynamic channel data. When a malicious RDP target sends dynamic channel data concurrently as the front-end client initiates disconnection, the proxy may deallocate the ChannelData structure before the secondary thread has finished reading from it. This temporal mismatch allows the rogue thread to access memory that has already been returned to the system allocator or marked for reuse, leading to undefined behavior and typically resulting in a process crash due to invalid memory reads.
From an operational perspective, this vulnerability poses a significant risk to the availability of FreeRDP proxy services. Since the attack vector involves sending specifically crafted dynamic channel data from the remote RDP target side, it does not require authentication or prior access privileges on the proxied system itself. An attacker can exploit this flaw by establishing a connection and then triggering the session teardown while simultaneously injecting malicious payloads into the dynamic channels. The immediate consequence is the termination of the freerdp-proxy process, which constitutes a denial-of-service condition for any users relying on that proxy instance to facilitate remote desktop connections. In environments where FreeRDP proxies are used as gateways or load balancers for multiple concurrent sessions, such crashes can lead to widespread service disruption and potential cascading failures if not properly monitored and restarted by automated systems.
This vulnerability aligns with Common Weakness Enumeration identifier CWE-416, which describes use-after-free errors resulting from improper memory management practices that fail to ensure data is no longer referenced before deallocation. Furthermore, the exploitation technique maps to MITRE ATT&CK tactic T1529, specifically the system shutdown or reboot subcategory if the crash leads to service unavailability requiring manual intervention, though it primarily falls under availability impact categories within broader disruption frameworks. The cross-thread nature of the bug highlights a failure in synchronization mechanisms, such as mutexes or atomic operations, which are essential for protecting shared resources during state transitions like session termination.
To mitigate this vulnerability, organizations must upgrade FreeRDP to version 3.32.2 or later, where the memory management logic has been corrected to prevent access to freed structures. Implementing strict input validation and rate limiting on dynamic channel data can also reduce the likelihood of triggering race conditions during high-load scenarios. Additionally, deploying the proxy behind a reverse proxy with health checks that automatically restart crashed instances can help maintain service availability while patches are applied. Security teams should monitor logs for unexpected process terminations in freerdp-proxy processes as an indicator of potential exploitation attempts and ensure that all components within the remote access infrastructure adhere to current security baselines.