CVE-2026-109252 in FreeRDP
Summary
by MITRE • 10/12/2026
FreeRDP from 3.9.0 before 3.32.0 contains a NULL pointer dereference vulnerability in the RDPEAR NDR reader that allows malicious servers to crash clients via truncated KERB_RPC_INTERNAL_NAME data. Attackers can send a CreateApReqAuthenticatorReq with NameCount of two or more ending before the Names pointer, causing cleanup to dereference a null base and terminate the client.
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Analysis
by VulDB Data Team • 10/12/2026
The vulnerability identified in FreeRDP versions prior to 3.32.0 represents a critical security flaw within the Remote Desktop Protocol (RDP) implementation, specifically affecting the RDPEAR NDR reader component. This issue stems from an improper handling of truncated data structures during the authentication phase of the RDP connection process. The core technical deficiency lies in the parsing logic for KERB_RPC_INTERNAL_NAME objects, where the software fails to adequately validate pointer integrity before attempting memory access operations. When a malicious server sends a CreateApReqAuthenticatorReq message with a NameCount value indicating two or more names but truncates the data stream before the actual Names pointer is fully transmitted, the client-side parser proceeds under the assumption that valid pointers exist in memory. This discrepancy between the declared count and the available data leads to a state where subsequent cleanup routines attempt to dereference a null base address. The result of this operation is an immediate crash or termination of the FreeRDP client application, effectively causing a denial of service against the end user attempting to establish a remote desktop session.
From a technical perspective, this vulnerability aligns with CWE-476, which describes NULL Pointer Dereference vulnerabilities. These flaws occur when software attempts to use a pointer that has not been properly initialized or validated, resulting in undefined behavior and typically application crashes. In the context of network-facing services like FreeRDP, such errors are particularly dangerous because they can be triggered remotely by an attacker controlling the server endpoint. The attack vector involves crafting a malicious RDP authentication packet that exploits the parser's lack of bounds checking on variable-length arrays or pointer lists within the NDR (Network Data Representation) format used for RPC communication. By manipulating the NameCount field while withholding the corresponding data, the attacker forces the client into an invalid memory state during the cleanup phase after parsing errors are detected but not handled gracefully.
The operational impact of this vulnerability is primarily a denial of service against FreeRDP clients connecting to untrusted or compromised RDP servers. While the immediate effect is application termination rather than arbitrary code execution, such crashes can be leveraged in broader attack scenarios. For instance, an attacker could use repeated crash attempts as part of a resource exhaustion strategy to disrupt availability for multiple users. Furthermore, if this NULL pointer dereference occurs during complex memory management operations, it may potentially lead to more severe consequences depending on the specific compiler optimizations and runtime environment, although the primary reported impact is stability failure. This vulnerability highlights the risks associated with parsing untrusted network input in security-critical protocols where robust error handling is essential for maintaining service continuity.
Mitigation strategies focus primarily on updating the FreeRDP software to version 3.32.0 or later, where this specific parsing flaw has been addressed through improved validation of pointer fields and enhanced bounds checking within the RDPEAR NDR reader. Organizations relying on FreeRDP should prioritize patching their client installations across all endpoints that connect to external RDP services. Additionally, network-level mitigations such as deploying intrusion detection systems capable of identifying anomalous RDP packet structures can provide an additional layer of defense against exploitation attempts from malicious servers. Security teams should also review their access control policies for RDP gateways to ensure that only trusted and verified server endpoints are accessible, thereby reducing the attack surface exposed to potential crafted packets designed to trigger this vulnerability.
This incident underscores the importance of rigorous input validation in protocol implementations, particularly when dealing with complex binary formats like NDR used in RPC communications. The ATT&CK framework categorizes such behaviors under techniques related to resource exhaustion and application crash exploitation, emphasizing that even non-code-execution vulnerabilities can significantly impact system availability and reliability. By addressing these parsing inconsistencies through software updates and enforcing strict network segmentation for RDP traffic, organizations can effectively neutralize the threat posed by this NULL pointer dereference flaw in FreeRDP.