Reachable assertion in FreeRDP - CVE-2026-121409
Published: November 10, 2026 / Updated: November 11, 2026
Vulnerability identifier: #VU164442
CSH Severity: Medium
CVSS v4: 8.2 [CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N]
CVE-ID: CVE-2026-121409
CWE-ID: CWE-617
Exploitation vector: Remote access
Exploit availability:
No public exploit available
Vulnerability details
The vulnerability allows a remote attacker to cause a denial of service by aborting assertion-enabled FreeRDP clients and configured proxies.
The vulnerability exists due to a reachable assertion in tpdu_write_header when nego_send_negotiation_request checks a 16-bit length limit instead of the one-byte X.224 limit. A remote attacker can supply oversized LoadBalanceInfo through server redirection or a 240–247-byte routing token to freerdp-proxy with FixedTarget=true and front-side RDP security without RDP_NEG_REQ, while outbound negotiation adds eight bytes, to trigger the assertion.
Affected software
FreeRDP
How to mitigate CVE-2026-121409
Install security update from vendor's website.
FreeRDP - update to 3.32.2