CVE-2026-5078 morgan vulnerable to Log Forging via unneutralized control characters in :remote-user
An attacker can inject forged log lines via control characters in the Authorization header, compromising log integrity for applications using morgan.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-5078?
CVE-2026-5078 is a medium-severity vulnerability in morgan, published on 3 Jun 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
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.
Weakness: CWE-117
Which versions are affected by CVE-2026-5078?
2 open source packages ship an affected version, including morgan. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
morgan npm | From 1.2.0 | 1.11.0 |
morgan npm | From 1.2.0 | 1.11.0 |
Products include Morgan Project Morgan.
How do I fix CVE-2026-5078?
Upgrade morgan to 1.11.0 or later.
Is CVE-2026-5078 being exploited?
There is no known exploitation of CVE-2026-5078 in the wild and no public exploit code.
Other vulnerabilities in morgan
Sources
Also known as CLSA-2026-1783904625, CLSA-2026-1784596308, DEBIAN-CVE-2026-5078, GHSA-4vj7-5mj6-jm8m, MINI-2c9r-9w23-79pr, MINI-9296-w7rg-c654 and 2 more.