CVE-2026-31884 in FreeRDP
Summary
by MITRE • 03/13/2026
FreeRDP is a free implementation of the Remote Desktop Protocol. Prior to 3.24.0, division by zero in MS-ADPCM and IMA-ADPCM decoders when nBlockAlign is 0, leading to a crash. In libfreerdp/codec/dsp.c, both ADPCM decoders use size % block_size where block_size = context->common.format.nBlockAlign. The nBlockAlign value comes from the Server Audio Formats PDU on the RDPSND channel. The value 0 is not validated anywhere before reaching the decoder. When nBlockAlign = 0, the modulo operation causes a SIGFPE (floating point exception) crash. This vulnerability is fixed in 3.24.0.
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Analysis
by VulDB Data Team • 05/13/2026
The vulnerability identified as CVE-2026-31884 affects FreeRDP, an open-source implementation of the Remote Desktop Protocol that enables remote desktop connections across various platforms. This security flaw exists in versions prior to 3.24.0 and specifically targets the ADPCM audio decoding components within the library. The issue manifests when processing audio data received through the RDPSND channel, which carries server audio formats information. The vulnerability stems from inadequate input validation of the nBlockAlign parameter, a critical field that defines the block alignment for audio data processing. This parameter originates from the Server Audio Formats PDU and is directly used in the audio decoding logic without proper verification of its validity.
The technical execution of this vulnerability occurs in the libfreerdp/codec/dsp.c file where both MS-ADPCM and IMA-ADPCM decoders perform a modulo operation using the formula size % block_size, with block_size being assigned from context->common.format.nBlockAlign. When an attacker can manipulate or inject malicious audio data with nBlockAlign set to zero, the modulo operation becomes mathematically invalid, resulting in a SIGFPE signal that terminates the application process. This represents a classic division by zero scenario that falls under CWE-369, which specifically addresses the condition where a division operation attempts to divide by zero. The vulnerability demonstrates a fundamental lack of input sanitization and validation within the audio processing pipeline, creating a crash condition that can be exploited to cause denial of service against FreeRDP clients.
The operational impact of this vulnerability extends beyond simple application crashes, as it provides an attacker with a reliable method to disrupt remote desktop sessions. Since FreeRDP is commonly used in enterprise environments for remote access and administration, this vulnerability could be leveraged to create persistent service disruptions or as part of broader attack campaigns targeting remote desktop infrastructure. The attack vector requires the ability to influence audio data transmission through the RDPSND channel, which is typically accessible during active remote desktop connections. This vulnerability aligns with ATT&CK technique T1499.004, which covers network disruption through service interruption, and represents a critical weakness in the protocol implementation that could potentially be chained with other vulnerabilities to achieve more sophisticated attack objectives.
The mitigation for CVE-2026-31884 is straightforward and involves upgrading to FreeRDP version 3.24.0 or later, where the fix implements proper validation of the nBlockAlign parameter before it is used in arithmetic operations. This remediation addresses the root cause by ensuring that block alignment values of zero are rejected or handled gracefully, preventing the execution of invalid modulo operations. Security practitioners should prioritize this update across all systems utilizing FreeRDP for remote desktop connections, particularly in environments where remote access is critical to business operations. The fix demonstrates proper defensive programming practices that should be implemented throughout similar audio processing pipelines, emphasizing the importance of input validation and error handling in security-critical software components. Organizations should also consider implementing network monitoring to detect unusual audio data patterns that might indicate exploitation attempts, while maintaining regular patch management schedules to address similar vulnerabilities in the future.