CVE-2026-5078CWE-117

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

Medium · published June 3, 2026

CVSS v3.1
5.3
EPSS
0%
Percentile
34.7
In the wild
Unconfirmed
What it is

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.

The record
Technical detail
CVSS v3.1
5.3 · MEDIUM
Vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N
CVSS v4.0
Not supplied
EPSS
0.00415 · 34.7th percentile
Weakness
CWE-117 · Improper Output Neutralization for Logs
Published
2026-06-03T05:56Z
EPSS history
Timeline
  • 03 JUN 05:56Z
    morgan vulnerable to Log Forging via unneutralized control characters in :remote-user
    cvelistv5