CVE-2026-55194
Description
A flaw was found in FreeRDP. A remote attacker, specifically a malicious TS Gateway, can exploit a heap-buffer-overflow vulnerability by sending a specially crafted Remote Desktop Protocol (RDP) response. This occurs because the client incorrectly uses a smaller alloc_hint value instead of the actual StubLength for buffer capacity during response reassembly. This allows attacker-controlled data to be written beyond the intended buffer, leading to a client crash and potentially enabling arbitrary code execution.
Statement
A heap buffer overflow flaw was found in FreeRDP's TS Gateway RPC client (libfreerdp/core/gateway/rpc_client.c). During response fragment reassembly in rpc_client_recv_fragment, stream allocation relies on the server-provided alloc_hint rather than the actual StubLength. A malicious TS Gateway can send a PTYPE_RESPONSE packet with a small alloc_hint and a larger payload, causing Stream_Write to overwrite memory beyond the fixed 4096-byte buffer (pdu->s). This can result in client crashes or potential arbitrary code execution.
Mitigation
To mitigate this vulnerability, avoid connecting through untrusted TS Gateways (RD Gateways) or disable gateway parameters (such as omitting `/g:` in `xfreerdp`) to force direct RDP connections and bypass RPC response parsing.
Common Vulnerability Scoring System (CVSS) Score Details
Info alert:Important note
CVSS scores for open source components depend on vendor-specific factors (e.g. version or build chain). Therefore, Red Hat's score and impact rating can be different from NVD and other vendors. Red Hat remains the authoritative CVE Naming Authority (CNA) source for its products and services (see Red Hat classifications).
CVSS v3 Score Breakdown
| Red Hat | NVD | cve.org | |
|---|---|---|---|
| Base Score | 8.8 | N/A | N/A |
| Attack Vector | Network | N/A | N/A |
| Attack Complexity | Low | N/A | N/A |
| Privileges Required | None | N/A | N/A |
| User Interaction | Required | N/A | N/A |
| Scope | Unchanged | N/A | N/A |
| Confidentiality | High | N/A | N/A |
| Integrity Impact | High | N/A | N/A |
| Availability Impact | High | N/A | N/A |
Vector
Red Hat: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
Understanding the Weakness (CWE)
Integrity,Confidentiality,Availability
Technical Impact: Modify Memory; Execute Unauthorized Code or Commands
Buffer overflows often can be used to execute arbitrary code, which is usually outside the scope of the product's implicit security policy. This can often be used to subvert any other security service.
Availability
Technical Impact: Modify Memory; DoS: Crash, Exit, or Restart; DoS: Resource Consumption (CPU)
Buffer overflows generally lead to crashes. Other attacks leading to lack of availability are possible, including putting the product into an infinite loop.
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