CVE-2026-91963 in FreeRDP
Summary
by MITRE • 09/15/2026
FreeRDP versions before 3.31.0 contain an uninitialized heap memory disclosure vulnerability in the urbdrc USB redirection channel. A malicious RDP server can induce failing USB transfers to read uninitialized heap memory from the client, defeating ASLR and enabling remote code execution when chained with memory corruption vulnerabilities.
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Analysis
by VulDB Data Team • 09/15/2026
The vulnerability identified in FreeRDP versions prior to 3.31.0 represents a critical security flaw within the urbdrc USB redirection channel component of the Remote Desktop Protocol implementation. This issue is classified as an uninitialized heap memory disclosure, which falls under the Common Weakness Enumeration category CWE-947 for improper initialization of public data members and often overlaps with CWE-200 for exposure of sensitive information to an unauthorized actor. The core technical flaw arises from a failure in the software to properly initialize specific memory buffers allocated on the heap before they are utilized during USB transfer operations. In standard secure programming practices, any memory block obtained from the heap must be explicitly zeroed or initialized with valid data prior to use to prevent the leakage of residual information that may remain from previous allocations by other processes or system components.
When a malicious RDP server interacts with this vulnerable client implementation, it can induce specific conditions where USB transfers fail or are manipulated in such a way that the uninitialized memory regions are exposed rather than overwritten or properly handled. This exposure allows an attacker to read arbitrary contents of the client's heap space. The operational impact of this disclosure is severe because it directly undermines Address Space Layout Randomization ASLR, a fundamental operating system security feature designed to randomize the memory locations of key data areas such as base addresses for executables and libraries to prevent exploitation of buffer overflow vulnerabilities. By leaking pointers or other sensitive data structures from uninitialized heap regions, an attacker can determine the exact memory layout of the target process, effectively neutralizing ASLR protections.
The severity of this vulnerability is further amplified by its potential to serve as a precursor to remote code execution RCE. While the initial flaw provides information disclosure, it creates a reliable mechanism for defeating security mitigations that would otherwise hinder exploitation attempts. When chained with other memory corruption vulnerabilities such as heap overflows or use-after-free conditions within the same application context, this uninitialized memory read can provide an attacker with the precise addresses needed to craft exploit payloads that redirect execution flow to malicious code injected into the process space. This combination transforms a simple information leak into a critical remote code execution vector, allowing full compromise of the client system under specific circumstances where additional vulnerabilities are present or exploitable through similar mechanisms.
Mitigation strategies for this vulnerability primarily involve updating FreeRDP to version 3.31.0 or later, which includes patches that ensure proper initialization of heap memory buffers within the urbdrc channel before they are exposed during USB redirection operations. Organizations relying on remote desktop services should prioritize patching their client infrastructure immediately given the high severity and the potential for chaining with other vulnerabilities. Additionally, defense-in-depth measures such as enabling strict ASLR policies at the operating system level and employing application whitelisting can help mitigate the impact of exploitation attempts even if a vulnerability is present. Monitoring network traffic for anomalous USB redirection patterns may also assist in detecting attempted exploitation activities in real-time environments where immediate patching is not feasible.