JavaScript DOM XSS via fetch().json() → insertAdjacentHTML not detected by CodeQL

Inizia con la suite di query di sicurezza security-extended di JavaScript e verifica come vengono modellate le risposte di fetch().json() e insertAdjacentHTML. Determina se questo flusso è escluso intenzionalmente o se richiede la modellazione di una sorgente e di un sink, quindi convalida la conclusione rispetto all’esempio fornito e conferma se è previsto un risultato XSS.

Description of the false positive

We are trying to better understand the design decisions behind JavaScript XSS detection in CodeQL, specifically around taint sources involving network responses.

I have a piece of client-side JavaScript that builds HTML using insertAdjacentHTML with values coming from a fetch().json() response. From an application-security perspective, this is treated as a potential DOM XSS risk in our project, but CodeQL does not report it.

I’d like to confirm whether this behavior is by design, and if so, what the recommended way is to model this trust boundary.

Code samples or links to source code

            function loadMessageLogs(pageSize, continuationToken) {
                let url = '?handler=LoadMessageLogs&pageSize=' + pageSize;
                if (continuationToken)
                    url += '&continuationToken=' + encodeURIComponent(continuationToken);

                fetch(url)
                    .then(response => response.json())
                    .then(data => {
                        const tbody = document.querySelector("#tblMessageLogs tbody");
                        tbody.innerHTML = "";

                        if (!data.items || data.items.length === 0) {
                            messageLogs.hidden = true;
                            noMessageLogs.hidden = false;
                        }
                        else {

                            data.items.forEach(item => {
                                const link = `<a href="/MessageLogs/Details/${item.messageId}">View message</a>`;
                                const row = `<tr>
                                        <td>${item.createdDate}</td>
                                        <td>${item.messageId}</td>
                                        <td>${item.interfaceId ?? ''}</td>
                                        <td>${item.target ?? ''}</td>
                                        <td>${item.mpanCore ?? ''}</td>
                                        <td>${item.meterId ?? ''}</td>
                                        <td>${link}</td>
                                        </tr>`;
                                tbody.insertAdjacentHTML('beforeend', row);
                            });

                            PagingModule.updatePaging(data.continuationToken)
                            messageLogs.hidden = false;
                            noMessageLogs.hidden = true;
                        }
                    });
            }

In our case, data.items[*] ultimately contains data that may originate from user input stored and returned by the backend.

• We are running the javascript-security-extended query suite.
• No XSS issue is reported for this code.