CVE-2026-23948 in FreeRDP
Summary
by MITRE • 02/09/2026
FreeRDP is a free implementation of the Remote Desktop Protocol. Prior to 3.22.0, a NULL pointer dereference vulnerability in rdp_write_logon_info_v2() allows a malicious RDP server to crash FreeRDP proxy by sending a specially crafted LogonInfoV2 PDU with cbDomain=0 or cbUserName=0. This vulnerability is fixed in 3.22.0.
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Analysis
by VulDB Data Team • 02/25/2026
The vulnerability identified as CVE-2026-23948 represents a critical NULL pointer dereference flaw within FreeRDP's implementation of the Remote Desktop Protocol. This issue affects versions prior to 3.22.0 and specifically targets the rdp_write_logon_info_v2() function which handles the processing of LogonInfoV2 PDUs. The flaw arises from insufficient input validation when processing authentication data from remote RDP servers, creating a potential denial of service condition that can be exploited by malicious actors. The vulnerability demonstrates a classic software security weakness where improper handling of edge cases leads to system instability.
The technical implementation of this vulnerability stems from the function's failure to properly validate the cbDomain and cbUserName fields within the LogonInfoV2 PDU structure. When these fields are set to zero by a malicious RDP server, the function attempts to dereference NULL pointers during subsequent processing operations. This pattern aligns with CWE-476 which categorizes NULL pointer dereference as a common weakness in software implementations. The vulnerability operates at the protocol level within FreeRDP's proxy functionality, making it particularly dangerous as it can be triggered during legitimate RDP authentication sequences.
From an operational perspective, this vulnerability creates significant risk for organizations relying on FreeRDP proxy implementations for remote desktop services. Attackers can exploit this weakness by establishing a malicious RDP server connection and sending crafted LogonInfoV2 PDUs with zero-length domain and username fields. The resulting crash of the FreeRDP proxy service can lead to denial of service conditions that disrupt legitimate remote access operations. This vulnerability falls under the ATT&CK technique T1499.004 which covers network disruption and can be classified as a service disruption attack vector. The impact extends beyond simple availability issues as it can be used to interrupt critical remote access infrastructure.
Organizations should immediately implement mitigation strategies including updating to FreeRDP version 3.22.0 or later, which contains the necessary patches for this vulnerability. Network segmentation and monitoring of RDP traffic can help detect potential exploitation attempts. Additionally, implementing proper input validation and sanitization measures at the proxy level can provide defense-in-depth protection. Security teams should also consider deploying intrusion detection systems that can identify suspicious LogonInfoV2 PDU patterns and monitor for abnormal proxy service behavior. The vulnerability highlights the importance of robust input validation in protocol implementations and demonstrates how seemingly minor edge case handling can lead to significant security implications.