CVE-2026-121961
Description
A flaw was found in FreeRDP. A malicious or compromised Remote Desktop Protocol (RDP) server can trigger a race condition by repeatedly requesting the creation of an already active dynamic virtual channel while client data is concurrently processed. This issue leads to a use-after-free condition, allowing the server to crash the proxy process and result in a Denial of Service (DoS).
Statement
This vulnerability is rated Moderate rather than Important because successful exploitation only results in a denial of service and requires a specific, non-default proxy configuration. Under typical Red Hat enterprise deployments, the freerdp-proxy component is not configured to intercept dynamic virtual channels by default. Furthermore, triggering the condition requires routing an active client session to an untrusted or compromised backend RDP server and winning a multi-threaded timing race to terminate the proxy process.
Mitigation
To mitigate this issue, disable dynamic virtual channel interception in freerdp-proxy and restrict target connections to trusted hosts:
1. Operational Configuration: Ensure the proxy configuration does not specify `Intercept=drdynvc` and do not enable proxy modules that intercept dynamic virtual channels. Without dynamic channel interception enabled, the vulnerable tracker path is not invoked.
2. Network Access Controls: Restrict outbound proxy traffic exclusively to verified, trusted target RDP servers using network egress firewall rules.
Caveats: Disabling dynamic channel interception may prevent inspection or custom processing of dynamic virtual channel features. Modifying proxy configurations requires restarting the freerdp-proxy process, which will terminate active client sessions.
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).
The following CVSS metrics and score provided are preliminary and subject to review.
CVSS v3 Score Breakdown
| Red Hat | NVD | cve.org | |
|---|---|---|---|
| Base Score | 5.9 | N/A | 5.9 |
| Attack Vector | Network | N/A | Network |
| Attack Complexity | High | N/A | High |
| Privileges Required | None | N/A | None |
| User Interaction | None | N/A | None |
| Scope | Unchanged | N/A | Unchanged |
| Confidentiality | None | N/A | None |
| Integrity Impact | None | N/A | None |
| Availability Impact | High | N/A | High |
Vector
Red Hat: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
cve.org: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
Understanding the Weakness (CWE)
Confidentiality
Technical Impact: Read Memory
If the expired pointer is used in a read operation, an attacker might be able to control data read in by the application.
Availability
Technical Impact: DoS: Crash, Exit, or Restart
If the expired pointer references a memory location that is not accessible to the product, or points to a location that is "malformed" (such as NULL) or larger than expected by a read or write operation, then a crash may occur.
Integrity,Confidentiality,Availability
Technical Impact: Execute Unauthorized Code or Commands
If the expired pointer is used in a function call, or points to unexpected data in a write operation, then code execution may be possible.
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