CVE-2026-91951 FreeRDP CVE debrief

Who should care

Defenders responsible for FreeRDP deployments should assess exposure and prioritize patching to prevent potential denial-of-service attacks. Affected deployments should review and update incident response plans to address potential disruptions to RDP services. Defenders should verify FreeRDP versions and apply patches to prevent potential denial-of-service attacks.

Why it matters

Defenders should prioritize verifying FreeRDP versions and applying patches to prevent potential denial-of-service attacks. The vulnerability allows a malicious RDP server to send a crafted USB redirection message, triggering an out-of-bounds write. Affected deployments should review and update incident response plans.

• Denial of service when verbose asserts are enabled
• Potential disruption to RDP services
• Need for verification of FreeRDP versions and patching

Technical summary

FreeRDP versions before 3.31.0 contain an out-of-bounds write vulnerability in the urbdrc client channel's urb_send_current_frame_number_result() function. A malicious RDP server can send a crafted 28-byte USB redirection message to trigger a 4-byte write past the allocated 16-byte buffer, causing denial of service when verbose asserts are enabled. The vulnerability affects FreeRDP deployments, and defenders should assess exposure and prioritize patching to prevent potential denial-of-service attacks. Affected deployments should review and update incident response plans to address potential disruptions to RDP services.

Defensive priority

Defenders should prioritize verifying FreeRDP versions and applying patches to prevent potential denial-of-service attacks.

Recommended defensive actions

• Verify FreeRDP versions and apply patches
• Monitor for potential denial-of-service attacks
• Review and update incident response plans
• Confirm whether affected product deployments exist in managed environments and assign an owner for follow-up
• Plan vendor-supported updates or mitigations through normal change control where exposure is confirmed
• Check relevant monitoring, detection, and logs for exposed assets that need extra review
• Track exceptions, retest remediated assets, and close the item only after evidence is documented

Evidence notes

The CVE record and NVD entry provide details on the vulnerability, but additional information on affected versions and remediation is limited. Defenders should verify FreeRDP versions and apply patches to prevent potential denial-of-service attacks. The vulnerability allows a malicious RDP server to send a crafted 28-byte USB redirection message, triggering a 4-byte write past the allocated 16-byte buffer.

Sources and references

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.