CVE-2026-73242 in FreeRDP
Summary
by MITRE • 08/11/2026
FreeRDP is a free implementation of the Remote Desktop Protocol. Prior to 3.30.0, FreeRDP's winpr/libwinpr/sspi/Kerberos/kerberos.c kerberos_DecryptMessage function fails to bound the peer-controlled GSS Wrap-token EC field before using it with RRC in IOV pointer offsets, allowing a malicious RDP peer to trigger out-of-bounds reads and in-place writes during CredSSP/NLA Kerberos decryption. This issue is fixed in version 3.30.0.
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Analysis
by VulDB Data Team • 08/11/2026
The vulnerability exists within FreeRDP's implementation of the Remote Desktop Protocol, specifically in the kerberos_DecryptMessage function located in winpr/libwinpr/sspi/Kerberos/kerberos.c. This flaw represents a classic buffer overflow condition that occurs when processing GSS Wrap tokens during CredSSP/NLA Kerberos decryption operations. The issue stems from inadequate bounds checking on peer-controlled data fields, particularly the EC (Encryption Context) field within the GSS Wrap-token structure.
The technical implementation flaw allows an attacker to manipulate the EC field value in a way that bypasses normal input validation mechanisms. When the system processes this malformed token, it uses the unbounded EC field value as an index or offset parameter within IOV (Input/Output Vector) pointer operations. This creates a scenario where the application reads from memory locations beyond its allocated buffers or writes data to arbitrary memory positions. The vulnerability specifically affects the RRC (Remote Desktop Credentials) processing pipeline during authentication and encryption operations.
The operational impact of this vulnerability is significant as it enables remote code execution capabilities through a malicious RDP peer connection. An attacker who can establish an RDP session with a vulnerable FreeRDP implementation can craft specially crafted GSS Wrap tokens that trigger out-of-bounds memory reads and writes. This allows for information disclosure, memory corruption, and potentially full system compromise. The vulnerability is particularly dangerous in environments where RDP services are exposed to untrusted networks or where credential validation occurs through CredSSP/NLA protocols.
This vulnerability aligns with CWE-129, which covers improper validation of array index bounds, and represents a specific instance of improper input validation that leads to memory corruption. From an ATT&CK perspective, this issue maps to T1075 (Pass the Hash) and T1566 (Phishing for Information) techniques as attackers could exploit this to escalate privileges or gain unauthorized access. The mitigation strategy requires updating to FreeRDP version 3.30.0 or later, which implements proper bounds checking on the EC field before using it in memory operations. Additional defensive measures include network segmentation, RDP port restrictions, and monitoring for unusual authentication patterns that might indicate exploitation attempts.
The fix implemented in version 3.30.0 addresses the root cause by introducing proper input validation and boundary checks on peer-controlled data fields. The updated implementation ensures that all EC field values are validated against expected ranges before being used in IOV pointer calculations, preventing both read and write operations beyond allocated memory boundaries. This represents a standard defensive programming practice that aligns with secure coding guidelines for network protocol implementations. Organizations should prioritize immediate deployment of this patch while also implementing additional security controls such as multi-factor authentication and network access controls to reduce the attack surface for RDP services.