CVE-2026-5078 PUBLISHED

morgan vulnerable to Log Forging via unneutralized control characters in :remote-user

Assigner: openjs
Reserved: 28.03.2026 Published: 03.06.2026 Updated: 03.06.2026

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.

Metrics

CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N
CVSS Score: 5.3

Product Status

Vendor morgan
Product morgan
Versions Default: unaffected
  • affected from 1.2.0 to 1.10.1 (incl.)
  • Version 1.11.0 is unaffected

Credits

  • Yuki Matsuhashi reporter
  • Ulises Gascón remediation developer
  • Jon Church remediation developer

References

Problem Types

  • CWE-117: Improper Output Neutralization for Logs CWE