CVE-2026-23732 in FreeRDP
Summary
by MITRE • 01/19/2026
FreeRDP is a free implementation of the Remote Desktop Protocol. Prior to version 3.21.0, FastGlyph parsing trusts `cbData`/remaining length and never validates against the minimum size implied by `cx/cy`. A malicious server can trigger a client‑side global buffer overflow, causing a crash (DoS). Version 3.21.0 contains a patch for the issue.
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Analysis
by VulDB Data Team • 01/31/2026
The vulnerability identified as CVE-2026-23732 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 3.21.0 and represents a critical buffer overflow condition that can be exploited by malicious remote servers to disrupt client operations. The vulnerability specifically impacts the FastGlyph parsing functionality within the RDP implementation, which is responsible for handling graphical elements in remote desktop sessions.
The technical root cause of this vulnerability lies in improper validation of buffer sizes during FastGlyph processing. When FreeRDP processes glyph data from a remote server, it relies on the `cbData` field which indicates the remaining data length, without performing adequate validation against the minimum size requirements implied by the `cx` and `cy` dimensions. This trust-based approach allows a malicious server to craft specially crafted glyph data where the reported data size does not match the actual graphical dimensions, creating a scenario where client-side memory allocation becomes invalid. The absence of proper bounds checking means that the client will attempt to read beyond allocated buffer boundaries, resulting in a global buffer overflow condition.
The operational impact of this vulnerability is significant as it enables a remote attacker to execute a denial-of-service attack against any FreeRDP client that has not been updated to version 3.21.0 or later. When exploited, the buffer overflow causes the client application to crash immediately, terminating the remote desktop session and disrupting user productivity. This vulnerability is particularly dangerous in enterprise environments where remote desktop services are extensively used, as it can be leveraged to repeatedly disrupt critical business operations without requiring authentication or complex exploitation techniques. The simplicity of the attack vector makes it especially concerning for environments where security controls may be less stringent.
The vulnerability aligns with CWE-121, which describes stack-based buffer overflow conditions, and more specifically relates to improper validation of input parameters in graphical rendering components. From an ATT&CK framework perspective, this vulnerability maps to T1499.004, which covers network denial of service attacks, and potentially T1566.001 for initial access through malicious remote desktop connections. Organizations should prioritize updating their FreeRDP implementations to version 3.21.0 or later to remediate this vulnerability. Additionally, network segmentation and monitoring of remote desktop traffic can provide additional defense-in-depth measures while the update is being deployed. Security teams should also consider implementing access controls and limiting exposure of remote desktop services to reduce the attack surface for potential exploitation of this and similar vulnerabilities.