Impact

Morgan's :remote-user token extracts the Basic auth username from the Authorization header and writes it to the log stream without neutralizing control characters. An attacker can send a crafted Authorization: Basic header containing CR/LF characters to inject forged log lines, corrupting the one-request-per-line structure of access logs.

The built-in combined, common, default, and short formats are affected, as well as any custom format that includes :remote-user.

Patches

Users should upgrade to version 1.11.0.

Workarounds

Use a custom format string that does not include :remote-user.

morgan is an HTTP request logger middleware for Node.js. In versions prior to 1.12.0, the internal helper that escapes log token values did not neutralize the Unicode line separator characters U+0085 (Next Line), U+2028 (Line Separator), and U+2029 (Paragraph Separator). An unauthenticated remote client can place these characters in an attacker-controlled log token, for example a Basic auth username surfaced through the remote-user token, so that Unicode-aware downstream log processing splits 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, which only addressed ASCII control characters. The issue is fixed in morgan 1.12.0, which extends the escaping set to cover these Unicode line separators. Upgrade to morgan 1.12.0 to remediate.