CVE-2026-109257 in FreeRDP
Summary
by MITRE • 10/12/2026
FreeRDP before 3.32.0 contains a double-free vulnerability in nsc_context_initialize_encode() that leaves dangling plane pointers after a partial buffer growth failure. Attackers using a crafted RDP client can negotiate NSCodec with a large desktop geometry to trigger allocation failure, crashing the server during context teardown.
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Analysis
by VulDB Data Team • 10/12/2026
The identified vulnerability resides within the FreeRDP implementation prior to version 3.32.0 and specifically affects the nsc_context_initialize_encode function, which is responsible for initializing encoding contexts for NSCodec compression operations. This flaw manifests as a double-free condition that occurs during the teardown phase of context initialization when buffer growth fails due to insufficient memory allocation. The root cause lies in improper error handling logic where pointer management is not correctly synchronized with allocation outcomes. When an attacker negotiates NSCodec support and specifies a large desktop geometry, the server attempts to allocate buffers for encoding operations. If this allocation fails or results in a partial failure state, the cleanup routine incorrectly proceeds to free memory pointers that have already been released or are no longer valid, resulting in dangling plane pointers within the internal data structures.
From an operational perspective, this vulnerability allows remote attackers who can establish an RDP connection and negotiate NSCodec compression with specific geometric parameters to trigger a denial of service condition. By crafting requests that induce allocation failures during context initialization, the attacker forces the server into an unstable state where it attempts to double-free memory regions. This typically results in application crashes or segmentation faults within the FreeRDP process, effectively disrupting availability for legitimate users relying on remote desktop services. The attack does not require authentication bypass but relies on the ability to initiate a session and negotiate specific compression settings that exceed available resources or trigger internal allocation limits.
This vulnerability aligns with CWE-415 Double Free, which describes errors where memory is freed more than once, leading to heap corruption and potential code execution if exploited further in other contexts. Although primarily observed here as causing crashes, double-free vulnerabilities are frequently associated with higher severity outcomes such as arbitrary code execution due to the manipulation of heap metadata structures like free chunks or size fields. In terms of threat modeling, this behavior corresponds to ATT&CK technique T1499 Endpoint Denial of Service, specifically under sub-techniques involving resource exhaustion or application crashes through malformed inputs. The vulnerability highlights critical gaps in input validation and memory management safety checks within the compression module initialization path.
Mitigation strategies primarily involve upgrading FreeRDP to version 3.32.0 or later where this issue has been addressed by correcting the pointer handling logic during buffer allocation failures. Until an upgrade is feasible, administrators should consider restricting NSCodec negotiation for untrusted clients or implementing network-level access controls that limit which hosts can initiate RDP sessions with compression enabled. Additionally, deploying intrusion detection systems capable of identifying anomalous patterns in RDP handshake sequences involving unusually large desktop geometry parameters may provide a layer of defense against exploitation attempts. Regular patch management and adherence to vendor security advisories remain the most effective long-term solution for maintaining the integrity and availability of remote desktop infrastructure relying on FreeRDP components.