CVE-2026-109677 in FreeRDP
Summary
by MITRE • 10/13/2026
FreeRDP from 2.0.0-beta1 before 3.28.0 contains an out-of-bounds read vulnerability in smartcard_LocateCardsByATRA_Call because the ATR pattern cbAtr byte count is not capped. Malicious RDP servers can send crafted ATR mask arrays to use query timing as an oracle, leaking heap memory bit-by-bit to defeat ASLR and aid RCE exploits.
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Analysis
by VulDB Data Team • 10/13/2026
The vulnerability identified in FreeRDP versions ranging from 2.0.0-beta1 up to but not including 3.28.0 represents a critical security flaw within the smartcard authentication subsystem, specifically located in the function responsible for locating cards by their Answer To Reset (ATR) patterns. This component is integral to the Remote Desktop Protocol implementation when it interacts with hardware tokens or smart card readers for multi-factor authentication. The core technical defect stems from an insufficient validation of input data regarding the byte count associated with ATR masks. When a client processes connection requests, it relies on these mask arrays to match against known smart card signatures. However, the code fails to enforce strict upper bounds on the cbAtr parameter, which dictates how many bytes are read or processed during this matching operation. This lack of boundary checking allows an attacker who controls the remote RDP server to supply a crafted ATR mask array that exceeds the expected buffer limits, triggering an out-of-bounds read condition within the client application's memory space.
The operational impact of this vulnerability extends far beyond simple data corruption or application crashes. Because the flaw results in reading memory locations outside the intended buffer boundaries, it enables a sophisticated side-channel attack vector known as timing-based oracle exploitation. By carefully crafting requests and measuring the response times from the FreeRDP client, an attacker can deduce information about the contents of adjacent heap memory blocks bit-by-bit. This technique leverages the fact that different memory access patterns or cache states may result in measurable time differences during execution. Over multiple iterations, this timing oracle allows the adversary to reconstruct sensitive data residing on the heap, including pointers and other metadata essential for bypassing modern operating system security mitigations such as Address Space Layout Randomization (ASLR). Once ASLR is defeated through memory leakage, the attacker gains a significant advantage in constructing reliable Remote Code Execution exploits by predicting the locations of critical libraries or functions within the process address space.
From a classification perspective, this vulnerability aligns with CWE-125, which describes Out-of-Bounds Read vulnerabilities where software reads data past the end, or before the beginning, of the intended buffer. Furthermore, the exploitation technique described falls under MITRE ATT&CK techniques related to Memory Scraping and potentially Defense Evasion through ASLR bypass methods like T1608 if linked with subsequent privilege escalation steps. The ability to leak heap memory bit-by-bit via timing channels is a sophisticated adversarial tactic that demonstrates how seemingly minor input validation failures can be escalated into full system compromise when combined with side-channel analysis techniques. This highlights the importance of not only preventing direct buffer overflows but also mitigating information disclosure vulnerabilities that facilitate advanced exploitation chains.
To mitigate this risk, organizations utilizing FreeRDP must immediately upgrade to version 3.28.0 or later, where the developers have implemented proper bounds checking for the cbAtr byte count parameter within the smartcard_LocateCardsByATRA_Call function. Until an update can be applied, network-level controls should restrict connections from untrusted RDP servers that might attempt to exploit this flaw. Additionally, enabling strict input validation policies and deploying intrusion detection systems capable of identifying anomalous timing patterns or malformed ATR structures in traffic flows can provide a layer of defense against active exploitation attempts. It is also advisable to review smart card integration configurations to ensure that only authorized authentication providers are permitted to interact with the FreeRDP client components, thereby reducing the attack surface available for such crafted requests.