morgan vulnerable to Log Injection via unescaped double quote in quoted log fields
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
Click a technology to see all vulnerabilities affecting it.
| Platform | Package | Vulnerable versions | Fixed in |
|---|---|---|---|
| npm package | morgan | < 1.12.1 | 1.12.1 |
References
- https://github.com/expressjs/morgan/security/advisories/GHSA-9f6g-j8ch-79g4
- https://nvd.nist.gov/vuln/detail/CVE-2026-87859
- https://github.com/expressjs/morgan/commit/4b695edf967ce179cdf4009fe8cddd184b7511ee
- https://cna.openjsf.org/security-advisories.html
- https://github.com/expressjs/morgan
- https://github.com/expressjs/morgan/releases/tag/1.12.1
- CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N- Weakness (CWE)
CWE-117- Platform
- npm
- Package
morgan- Disclosed
- 28.09.2026
- Updated
- 11.10.2026 10:22
Sources and licenses
OSV / GitHub Advisory Database - GHSA-9f6g-j8ch-79g4 - CC BY 4.0
Vulnerability history: morgan
All published vulnerabilities of this package (npm package), newest first. Shows whether this is a one-off slip or a package that needs watching.
- Total entries
- 4
- First → latest
- 03.2019 09.2026
- Without a fix
- 0
- Exploited in attacks
- 0
Severity breakdown
- Critical 1
- Medium 3
Disclosures per year
- 2019: 1
- 2020: 0
- 2021: 0
- 2022: 0
- 2023: 0
- 2024: 0
- 2025: 0
- 2026: 3
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morgan vulnerable to Log Injection via unescaped double quote in quoted log fields this entry
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