FreeRDP Heap Buffer Overflow in RDPSND Channel Enables Remote Code Execution
A heap-based buffer overflow in FreeRDP’s audio channel allows malicious RDP clients to execute code on servers running versions prior to 3.32.1.
Key points
- FreeRDP versions before 3.32.1 contain a heap-based buffer overflow in the server-side rdpsnd channel.
- The flaw stems from an integer wraparound in DVI_ADPCM block-alignment arithmetic that bypasses validation checks.
- Malicious clients can trigger unbounded heap writes by sending specific SNDC_FORMATS PDUs with incorrect alignment values.
FreeRDP before version 3.32.1 contains a heap-based buffer overflow vulnerability within its server-side rdpsnd channel component. This flaw allows remote attackers to execute arbitrary code on vulnerable systems. The vulnerability is rated as high severity by the National Vulnerability Database, with a CVSS score of 8.7. It affects any environment using the specified older versions of the FreeRDP library for Remote Desktop Protocol connections.
Root cause
The underlying issue is an integer wraparound error within the `rdpsnd_server_select_format()` function. Specifically, the arithmetic used for DVI_ADPCM block-alignment calculations fails to validate input correctly. This failure allows the validation logic to be bypassed entirely. As a result, the application processes malformed data without detecting the anomaly, leading to memory corruption during subsequent processing steps.
Attack path
An attacker initiates the exploit by connecting as a malicious RDP client to the vulnerable server. The client sends two `SNDC_FORMATS` Protocol Data Units containing crafted parameters. Specifically, the `nBlockAlign` value is set too small relative to the `nChannels` value. This mismatch triggers the integer wraparound during audio playback initialization. The server then performs an unbounded heap write, potentially allowing the attacker to execute arbitrary code on the host system.
Affected versions
- FreeRDP versions prior to 3.32.1 are affected by this vulnerability.
- Users running version 3.32.1 or later are not affected by this specific flaw.
- No other software products or libraries are mentioned as being impacted by this specific CVE.
Mitigation
- Upgrade FreeRDP to version 3.32.1 or any subsequent release that addresses this vulnerability.
- Restrict RDP access to trusted networks and authenticated users to reduce exposure to malicious clients.
- Monitor server logs for unusual audio channel activity or unexpected memory allocation errors.
Detection notes
Security teams should monitor for anomalous RDP session behaviors, particularly those involving rapid or malformed audio channel negotiations. Look for unexpected memory allocation spikes or heap corruption indicators in server logs during client connections. Check for failed validation events in the rdpsnd channel processing. If suspicious activity is detected, isolate the affected server immediately to prevent lateral movement. Review firewall logs for unauthorized RDP connection attempts from unknown sources.
What to do and how to stay safe: FreeRDP
- Verify the current version of FreeRDP installed on all servers and compare it against the vulnerable range.
- Apply the vendor-provided update to version 3.32.1 or newer as soon as possible to patch the flaw.
- Review recent RDP connection logs for any signs of unauthorized access or unusual client behavior.
- Implement network segmentation to limit exposure of RDP services to untrusted networks.
Step-by-step guide: Unpatched Software Myths: Why Common Beliefs Fail to Protect You
General security guidance from the BlueTeam Insider newsroom. It is not confirmed advice from the organisations named in this story.
Frequently asked questions
What is the CVSS score for CVE-2026-114045?
The National Vulnerability Database rates this vulnerability as high severity with a CVSS score of 8.7.
Which specific function contains the integer wraparound error?
The error is located in the `rdpsnd_server_select_format()` function within the rdpsnd channel.
Is there a patch available for this vulnerability?
Yes, upgrading to FreeRDP version 3.32.1 or later resolves this issue.
