FreeRDP CVE-2026-121397

Exploitation requires a victim FreeRDP client at version 3.32.1 or earlier, built with WINPR_UTILS_IMAGE_PNG, that connects to an attacker-controlled or compromised RDP server with clipboard redirection active. The server must offer a CF_DIB clipboard format carrying a 16 bpp BI_BITFIELDS DIB, and a local application on the client side must request that clipboard content as image/png (the clipboard_synthesize_image_bmp_to_png path exercised by the SDL3 client and any client converting CF_DIB to image/png via ClipboardGetData). Limiting factors: the attacker does not control the client directly but must induce the connection (passive user interaction, UI:P), clipboard redirection and the specific PNG conversion must occur, builds without WINPR_UTILS_IMAGE_PNG are unaffected, and only a limited amount of adjacent heap memory is leaked into the clipboard image rather than full memory read or code execution.

This is a moderate, not urgent, issue. The input CVSS is 5.3 (CVSS 4.0: AV:N/AC:L/AT:N/PR:N/UI:P with only VC:L, all other impacts N), reflecting a limited client-side memory disclosure rather than code execution. The vuln.today decision label is 'this_month' (not act_now/emergency), and there is no CISA KEV listing, so there is no confirmed active exploitation. No EPSS score was provided in the input, so probabilistic exploitation likelihood cannot be stated. The attack model is a 'reverse RDP' one: the victim's FreeRDP client must connect to a malicious or compromised RDP server (AV:N), and exploitation additionally depends on passive user interaction (UI:P) plus clipboard redirection and a local application requesting the clipboard as image/png - the SDL3 client path verified in the advisory. The impact is confined to leaking limited client heap bytes into a clipboard PNG (VC:L), with no integrity or availability impact for this specific over-read. Net: a real, confirmed bug worth patching on a normal cycle, but the preconditions (attacker-controlled server, specific clipboard conversion path, limited info leak) keep real-world risk well below what a raw network/unauthenticated label might suggest. Note the advisory bundles two additional process-abort/exit (DoS) defects in the same file, but the CVSS vector supplied here scores only the information-disclosure over-read (VA:N).

An attacker who operates or has compromised an RDP server lures a victim running a vulnerable FreeRDP-based client (e.g. the SDL3 client with clipboard redirection, versions <= 3.32.1). The server offers a 16 bpp BI_BITFIELDS CF_DIB clipboard image; when a local application asks the client for the clipboard as image/png, save_png_to_buffer reads 3 bytes per pixel from rows that hold only 2, embedding adjacent client heap bytes into the resulting PNG and disclosing client memory. A public PoC reproduction harness (ct.c) exists in the vendor advisory; it is not verified as working weaponized exploit code.