From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from lists1p.gnu.org (lists1p.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 9E2BBCD4851 for ; Tue, 12 May 2026 09:56:48 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists1p.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1wMjqN-0007ip-5u; Tue, 12 May 2026 05:56:03 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists1p.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1wMjqK-0007iY-VX for qemu-devel@nongnu.org; Tue, 12 May 2026 05:56:01 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1wMjqH-0005kK-EW for qemu-devel@nongnu.org; Tue, 12 May 2026 05:56:00 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1778579753; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding; bh=Dmh5471avZxbjWCnR/HxlXbeySRQyYNzD86VPgV3zJk=; b=QIFgJ8oLUOQ07lAUiZ+wY8o87P4e7HLEuYA1mKVDMSInc3eYrtwU6tlqeeX825xLLXZp18 pRHqLzM9DD9bACI53x5VAiQdLgOhuLXnk1tY7YOEiM5XrkmVdQEyBFVtqrTDgCny8RcRZ6 BdeiGeB4X15iWykniniHRkJEBhWCFms= Received: from mx-prod-mc-08.mail-002.prod.us-west-2.aws.redhat.com (ec2-35-165-154-97.us-west-2.compute.amazonaws.com [35.165.154.97]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-298-wrd10OheMhCBXzV-GNHxaQ-1; Tue, 12 May 2026 05:55:49 -0400 X-MC-Unique: wrd10OheMhCBXzV-GNHxaQ-1 X-Mimecast-MFC-AGG-ID: wrd10OheMhCBXzV-GNHxaQ_1778579748 Received: from mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.93]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-08.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 91CF31800359; Tue, 12 May 2026 09:55:48 +0000 (UTC) Received: from berrange.com (unknown [10.44.49.244]) by mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTP id 0159F18004A3; Tue, 12 May 2026 09:55:45 +0000 (UTC) From: =?UTF-8?q?Daniel=20P=2E=20Berrang=C3=A9?= To: qemu-devel@nongnu.org Cc: Feifan Qian , =?UTF-8?q?Marc-Andr=C3=A9=20Lureau?= , Heechan Kang , =?UTF-8?q?Daniel=20P=2E=20Berrang=C3=A9?= Subject: [PATCH] ui: fix validation of VNC extended clipboard data length Date: Tue, 12 May 2026 10:55:43 +0100 Message-ID: <20260512095543.459949-1-berrange@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.93 Received-SPF: pass client-ip=170.10.133.124; envelope-from=berrange@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -24 X-Spam_score: -2.5 X-Spam_bar: -- X-Spam_report: (-2.5 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.445, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H5=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: qemu development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org From: Heechan Kang QEMU's VNC extended clipboard handler inflates a client-controlled compressed clipboard payload. The code checks the declared text size against the total inflated buffer size: if (tsize < size) but then copies from: tbuf = buf + 4; qemu_clipboard_set_data(..., tsize, tbuf, true); The correct bound is the remaining data length after the 4-byte length field, not the total inflated buffer length. As a result, a VNC client can make QEMU copy up to 3 bytes past the end of the inflated heap buffer. With a second VNC client, those copied bytes are observable through the normal VNC extended clipboard PROVIDE path. Fixes: CVE-2026-8343 Reported-by: Heechan Kang Reported-by: Feifan Qian Reviewed-by: Daniel P. Berrangé Signed-off-by: Heechan Kang [DB: added #include and 'return' statements] Signed-off-by: Daniel P. Berrangé --- ui/vnc-clipboard.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-) diff --git a/ui/vnc-clipboard.c b/ui/vnc-clipboard.c index 124b6fbd9c..fa05d86f42 100644 --- a/ui/vnc-clipboard.c +++ b/ui/vnc-clipboard.c @@ -23,6 +23,7 @@ */ #include "qemu/osdep.h" +#include "qemu/error-report.h" #include "vnc.h" #include "vnc-jobs.h" @@ -282,10 +283,16 @@ void vnc_client_cut_text_ext(VncState *vs, int32_t len, uint32_t flags, uint8_t buf && size >= 4) { uint32_t tsize = read_u32(buf, 0); uint8_t *tbuf = buf + 4; - if (tsize < size) { + if (tsize <= size - 4) { qemu_clipboard_set_data(&vs->cbpeer, vs->cbinfo, QEMU_CLIPBOARD_TYPE_TEXT, tsize, tbuf, true); + } else { + error_report("vnc: malformed extended clipboard payload " + "with text length %u exceeding available %u", + tsize, size - 4); + vnc_client_error(vs); + return; } } } -- 2.54.0