CVE-2026-87859 · GHSA-9f6g-j8ch-79g4
morgan vulnerable to Log Injection via unescaped double quote in quoted log fields
- Risk score
- 44/100
- CVSS
- 5.3 v3.1
- Exploit chance (30 days)
- 0.4%
- Published
- 28 Sep 2026
Open in the live forecast Today's forecast
What to know
- What it is
- 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 …
- Affected
- morgan (npm) < 1.12.1
- Fix
- Upgrade morgan to 1.12.1 or later.
- Exploitation
- No known exploitation
Why it is Yellow
- CVSS 5.3 medium
- On your watchlist: npm
Affected packages
| Package | Ecosystem | Vulnerable | Fixed in |
|---|---|---|---|
| morgan | npm | < 1.12.1 | 1.12.1 |
References
- https://github.com/advisories/GHSA-9f6g-j8ch-79g4
- 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/releases/tag/1.12.1
- https://github.com/advisories/GHSA-9f6g-j8ch-79g4
Original description
### 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.
Last activity 28 Sep 2026. Patch Forecast updates every hour.