Improper Output Neutralization for Logs in morgan - CVE-2026-15603
Published: August 28, 2026
Vulnerability identifier: #VU146052
CSH Severity: Medium
CVSS v4: 6.9 [CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N]
CVE-ID: CVE-2026-15603
CWE-ID: CWE-117
Exploitation vector: Remote access
Exploit availability:
No public exploit available
Vulnerability details
The vulnerability allows a remote attacker to forge log entries.
The vulnerability exists due to improper output neutralization for logs in morgan access log token handling when logging attacker-controlled request data. A remote attacker can send crafted request values containing Unicode line separators to forge log entries.
The issue affects built-in formats including combined, common, default, and short, as well as custom formats. Downstream ECMAScript-aware or Unicode-aware log processing can split a single physical log record into multiple logical records.
Affected software
morgan
How to mitigate CVE-2026-15603
Install security update from vendor's website.
morgan - update to 1.12.0