# CVE-2026-15603: morgan vulnerable to Log Forging via unescaped Unicode line separators


- **Severity:** Medium 5.3 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N`)
- **Exploited in the wild:** Not known
- **Fix available:** Yes
- **Published:** 28 Aug 2026
- **Updated:** 28 Aug 2026
- **Also known as:** CLSA-2026-1788988321, CLSA-2026-1790108609, DEBIAN-CVE-2026-15603, GHSA-jxfw-x594-9x9m, MINI-6r4p-p49x-42cq, MINI-vhj5-2rj7-vmfr, UBUNTU-CVE-2026-15603

## What is CVE-2026-15603?

CVE-2026-15603 is a medium-severity vulnerability in morgan, published on 28 Aug 2026. 

### Official description

morgan is an HTTP request logger middleware for Node.js. In versions prior to 1.12.0, the internal helper that escapes log token values did not neutralize the Unicode line separator characters U+0085 (Next Line), U+2028 (Line Separator), and U+2029 (Paragraph Separator). An unauthenticated remote client can place these characters in an attacker-controlled log token, for example a Basic auth username surfaced through the remote-user token, so that Unicode-aware downstream log processing splits a single request log into multiple logical records. This is a log forging issue (CWE-117) and an incomplete-fix follow-up to CVE-2026-5078, which only addressed ASCII control characters. The issue is fixed in morgan 1.12.0, which extends the escaping set to cover these Unicode line separators. Upgrade to morgan 1.12.0 to remediate.

Weakness: CWE-117 (Improper Output Neutralization for Logs)

## Which versions are affected by CVE-2026-15603?

2 open source packages ship an affected version, including morgan. It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `morgan` | npm | All versions | 1.12.0 |
| `morgan` | npm | All versions | 1.12.0 |

Products: Morgan Project Morgan.

## How do I fix CVE-2026-15603?

Upgrade morgan to 1.12.0 or later.

## Is CVE-2026-15603 being exploited?

There is no known exploitation of CVE-2026-15603 in the wild and no public exploit code.

## Other vulnerabilities in morgan

- [CVE-2019-5413](https://insights.sbomify.com/CVE-2019-5413/): Code Injection in morgan (critical 9.8)
- [CVE-2026-5078](https://insights.sbomify.com/CVE-2026-5078/): morgan vulnerable to Log Forging via unneutralized control characters in :remote-user (medium 5.3)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-15603 and fix it if it is affected.

What it is: CVE-2026-15603 is a medium-severity vulnerability in morgan, published on 28 Aug 2026. 
Exploitation: There is no known exploitation of CVE-2026-15603 in the wild and no public exploit code.

Affected packages and fixed versions:
- morgan (npm): affected all versions; fixed in 1.12.0
- morgan (npm): affected all versions; fixed in 1.12.0

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-15603/ (Markdown: https://insights.sbomify.com/CVE-2026-15603/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-15603
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-15603
- OSV: https://osv.dev/vulnerability/CVE-2026-15603

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-15603/
Summaries are generated and may contain mistakes; the official description above is the record.