GHSA-9f6g-j8ch-79g4: Medium severity npm/morgan vulnerability
Impact
Morgan writes attacker-controlled request data to the access log. Its escaping (added in 1.11.0 and 1.12.0) neutralizes control characters, the Unicode line separators, and backslash, but not the double quote (0x22), which is the field delimiter of the Apache combined log format morgan emits. An attacker who controls a quoted field (:user-agent, :referrer, the request URL, or the Basic auth :remote-user) can inject a double quote to close the field early and forge additional fields in the log record. The combined, common, and default formats, and any custom format that quotes a token, are affected. This is an incomplete fix of CVE-2026-5078 and CVE-2026-15603.
Patches
Users should upgrade to version 1.12.1.
Workarounds
Update to version 1.12.1.
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade
npm/morganto a version that resolves this vulnerability.Fixed in 1.12.1 - Upgrade
Upgrade
morganto a version that resolves this vulnerability.Fixed in 1.12.1
Event History
Frequently Asked Questions
Which deployments are affected?
Deployments using Morgan's combined, common, or default log formats are affected. Custom formats are also affected if they place a token inside double quotes.
What does an attacker need to exploit this issue?
An unauthenticated remote attacker only needs to control a value written in a quoted log field, such as the User-Agent, Referer, request URL, or Basic authentication remote user. A double quote can terminate the field early and allow forged fields to be written into the log record.
How should this be remediated?
Upgrade Morgan to version 1.12.1. The provided workaround is also to update to version 1.12.1.