CVE-2026-121957 in FreeRDP
Summary
by MITRE • 11/04/2026
FreeRDP before 3.32.2 contains a use-after-free vulnerability that allows malicious RDP servers to corrupt client memory by racing the RDPGFX ResetGraphics handler against the planar bitmap decoder. Attackers can send ResetGraphics while concurrently sending compressed bitmaps of 32 bpp or more to trigger heap use-after-free or out-of-bounds read/write on shared planar buffers.
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Analysis
by VulDB Data Team • 11/04/2026
The vulnerability identified in FreeRDP versions prior to 3.32.2 represents a critical memory safety flaw rooted in improper synchronization mechanisms within the Remote Desktop Protocol client implementation. Specifically, this is classified as a use-after-free condition that arises from a race condition between two distinct processing paths: the RDPGFX ResetGraphics handler and the planar bitmap decoder. In normal operation, these components manage shared resources such as heap-allocated buffers used for rendering graphical data. However, due to insufficient locking or atomicity guarantees during state transitions, an attacker can manipulate the timing of incoming packets to exploit this window of inconsistency. When a malicious RDP server sends a ResetGraphics command concurrently with compressed bitmaps requiring thirty-two bits per pixel or higher color depth, it forces the client application to free memory associated with planar buffers while other threads may still hold references to that same memory region for decoding purposes.
From a technical perspective, this race condition allows an attacker to corrupt the heap by performing out-of-bounds reads or writes on shared planar buffers. The use-after-free aspect means that after the operating system reclaims the memory due to the reset operation, subsequent access attempts by the bitmap decoder operate on invalid pointers. This can lead to arbitrary code execution if the freed memory is reallocated and filled with attacker-controlled data before being accessed again. Alternatively, it may result in denial of service through application crashes caused by segmentation faults or illegal memory accesses. The complexity lies in the precise timing required to trigger this state; however, modern exploit development techniques often allow attackers to reliably induce such races under controlled network conditions, making this a viable attack vector against unpatched clients.
The operational impact of this vulnerability is severe for organizations relying on FreeRDP for remote access solutions. Successful exploitation could grant an attacker full control over the client machine by executing arbitrary code within the context of the vulnerable application process. This compromises confidentiality, integrity, and availability of sensitive data processed through the RDP session. Furthermore, because the attack originates from a malicious server rather than user interaction like clicking a link, it constitutes a passive threat that does not require social engineering to initiate. The vulnerability aligns with CWE-416, which describes use-after-free errors, and falls under MITRE ATT&CK technique T1203, specifically relating to exploitation for client-side execution via remote services. It also touches upon CWE-362 regarding concurrent execution race conditions that lead to security vulnerabilities.
Mitigation strategies must prioritize immediate patching of the FreeRDP installation to version 3.32.2 or later where these synchronization issues have been addressed by developers through improved locking mechanisms and validation checks before memory deallocation. In environments where updating is not immediately feasible, network segmentation should be enforced to restrict RDP connections only to trusted servers with verified integrity. Additionally, deploying intrusion detection systems capable of identifying anomalous patterns in RDP traffic may help detect attempted exploitation based on unusual packet timing or malformed header structures associated with the race condition trigger. Security teams should also ensure that all client endpoints are running updated operating system patches to mitigate potential secondary exploits leveraging heap corruption primitives often found alongside use-after-free flaws.