morgan vulnerable to Log Forging via unescaped Unicode line separators

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

5.3 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N

EPSS

• CVE-2026-15603: 0.40% estimated exploitation activity in the next 30 days; percentile 33.99 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Impact Morgan writes attacker-controlled request data to the access log through its tokens. The 1.11.0 fix neutralizes C0 control characters, DEL, and backslash, but it does not escape the Unicode line separators U+0085 (NEL), U+2028 (LINE SEPARATOR), or U+2029 (PARAGRAPH SEPARATOR). These code points are reachable through several tokens, including the request URL (:url), request headers such as :user-agent and :referrer, arbitrary :req[header] values, and the Basic auth username (:remote-user). NEL is valid obs-text in HTTP header values, so an attacker can place it in an ordinary request header. When such a value is logged, the raw code points survive into the emitted access-log record, and downstream ECMAScript-aware or Unicode-aware log processing splits the single physical record into multiple logical records. This allows an attacker to forge log entries. The built-in combined, common, default, and short formats are affected, as well as any custom format. This is an incomplete…

Published by the source

8 Sep 2026, 21:28 UTC

Last modified by the source

8 Sep 2026, 21:45 UTC

Source last checked

26 Oct 2026, 13:02 UTC

1. Revision 3 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-jxfw-x594-9x9m

2. Revision 2 · amended · 24 Oct 2026

   Amended from osv record GHSA-jxfw-x594-9x9m

3. Revision 1 · created · 23 Oct 2026

   Published from ghsa record GHSA-jxfw-x594-9x9m

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# Patch Next advisory brief: CVE-2026-15603

Advisory: morgan vulnerable to Log Forging via unescaped Unicode line separators
IDs: CVE-2026-15603, GHSA-jxfw-x594-9x9m
Record: https://patchnext.com/advisories/cve-2026-15603 (revision 3, source checked 26 Oct 2026, 13:02 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 5.3)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: morgan 1.12.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm morgan: affected < 1.12.0; fixed in 1.12.0

## Suggested inspection (read-only)
- `npm ls morgan --all`: lists every installed copy and version, including transitive ones. Run in the project root after `npm ci`.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on morgan.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-jxfw-x594-9x9m (GitHub-reviewed advisory GHSA-jxfw-x594-9x9m lists affected ranges: npm morgan >=0 <1.12.0)
- Verified: https://osv.dev/vulnerability/GHSA-jxfw-x594-9x9m (OSV record GHSA-jxfw-x594-9x9m lists affected ranges: npm morgan >=0 <1.12.0 (fixed))

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