CVE-2026-87859
MediumCVSS 5.3Summary
morgan is an HTTP request logger middleware for Node.js. In versions before 1.12.1, its escapeLogField() function does not escape the double quote character, which delimits the quoted fields of the Apache combined log format that morgan emits. An unauthenticated remote attacker who controls a value written to a quoted field, such as the User-Agent or Referer header, can include a double quote to close that field early, so a log consumer that parses the log by field position reads attacker-supplied text as the following field.
Risk Assessment
An attacker could forge log values, such as response status, potentially leading to incorrect analysis and concealment of actual activities. This may hinder incident detection and lead to flawed security decisions.
Recommendation
Update morgan to version 1.12.1 or later. Verify that log consumers properly handle quote escaping.
Other vulnerabilities in morgan
See all- CVE-2026-15603Medium
Morgan, an HTTP request logger middleware for Node.js, in versions prior to 1.12.0 did not neutralize the Unicode line separator characters U+0085, U+2028, and U+2029 in log token values. An unauthenticated remote client can place these characters in an attacker-controlled log token, such as a Basic auth username, causing downstream log processing to split a single request log into multiple logical records. This is a log forging issue (CWE-117) and an incomplete-fix follow-up to CVE-2026-5078. The issue is fixed in morgan 1.12.0.
- CVE-2026-5078Medium
Morgan, a popular Node.js logging middleware, has a log forgery vulnerability. The :remote-user token outputs the Basic Auth username without neutralizing control characters, allowing an attacker to inject forged log lines.
Original NVD description (English source)
morgan is an HTTP request logger middleware for Node.js. In versions before 1.12.1, its escapeLogField() function does not escape the double quote character, which delimits the quoted fields of the Apache combined log format that morgan emits. An unauthenticated remote attacker who controls a value written to a quoted field, such as the User-Agent or Referer header, can include a double quote to close that field early, so a log consumer that parses the log by field position reads attacker-supplied text as the following field. In the built-in formats this makes the recorded value differ from the value that was sent, and in custom formats that quote an attacker-controlled token before a server-controlled one it can forge values such as the response status. No newline is injected, so record separation stays intact. The issue is fixed in morgan 1.12.1, which escapes the double quote. Users should upgrade to morgan 1.12.1 or later.