CVE-2026-5078

Description

Impact: The morgan logging middleware's :remote-user token extracts the Basic auth username from the Authorization request header and writes it to the log stream without neutralizing control characters. An unauthenticated attacker can send a crafted Authorization Basic header containing CR or LF bytes to inject forged log lines, breaking the one-request-per-line structure of access logs and enabling log forgery against downstream log consumers. The built-in combined, common, default, and short formats are affected, as well as any custom format that references :remote-user. Affected versions: morgan 1.2.0 through 1.10.1. Patches: upgrade to morgan 1.11.0, which neutralizes control characters in the :remote-user token output. Workarounds: use a custom format string that does not include :remote-user.

CVSS Metrics

• v3.1•MEDIUM•Score: 5.3CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N

EPSS Trends

Current EPSS score: 0.25%• Percentile: 16%

Techniques & Countermeasures

• CWE-117•Improper Output Neutralization for Logs

  The product constructs a log message from external input, but it does not neutralize or incorrectly neutralizes special elements when the message is written to a log file.

Affected Systems

• morgan_project•morgan

  ≥ 1.2.0, < 1.11.0

• morgan•morgan

  ≥ 1.2.0, ≤ 1.10.1

• Npm•morgan

  ≥ 1.2.0, < 1.11.0

References (4)

• https://github.com/expressjs/morgan/security/advisories/GHSA-4vj7-5mj6-jm8m
• https://cna.openjsf.org/security-advisories.html
• https://nvd.nist.gov/vuln/detail/CVE-2026-5078
• https://github.com/expressjs/morgan