Insufficient escaping of unicode characters in query log

Vulnerability

CVE-2026-1337 arises from insufficient escaping of Unicode characters in the query log of Neo4j Enterprise and Community editions prior to version 2026.01. [1] Specifically, an authenticated user can inject control characters (e.g., newlines) via the metadata field of a Bolt transaction, causing the query log to contain unescaped HTML or fake log entries. [2] The log files are not sanitized for HTML, so opening them in a browser or HTML-aware viewer can trigger cross-site scripting (XSS).

Exploitation

Exploitation requires an authenticated Neo4j user with the ability to execute queries and attach custom metadata to a Bolt transaction. [2] The attacker crafts a metadata payload containing Unicode or control characters (e.g., \n plus arbitrary log lines). When the query is executed, the payload is written verbatim into the query log file. If an administrator or analyst subsequently opens that log file with a tool that treats it as HTML, the injected markup will be rendered, potentially executing script code. Alternatively, the injected newlines can produce fabricated log entries that mimic legitimate queries, enabling social engineering or audit trail manipulation. [2]

Impact

The primary impact is a client-side XSS attack against anyone who views the Neo4j query log in an HTML-capable viewer. The attacker could potentially steal cookies, session tokens, or perform actions within the log viewer’s context. Additionally, the log injection can obscure forensic evidence or mislead administrators by inserting fake query records. [2] However, the official advisory states there is no direct security impact on Neo4j server components themselves; the risk is confined to the log viewing process. [1]

Mitigation

Neo4j recommends treating query logs as plain text and not opening them in HTML-aware viewers unless using version 2026.01 or later. [1] The fix in version 2026.01 properly escapes Unicode and control characters before writing to the log file. Users on earlier versions should upgrade to the latest release. A proof of concept is available, but no active exploitation in the wild has been reported as of publication. [1][2]