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CVE-2026-15603

morgan vulnerable to Log Forging via unescaped Unicode line separators

MEDIUM
5.3
CVSS Score
Published: August 28, 2026 at 01:41 PM UTC
Updated: August 31, 2026 at 05:26 PM UTC
1 product affected across 1 vendorMorgan

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Severity
MEDIUM5.3
Exploit prediction
EPSS 0.4%
SSVC
No known exploit

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.

Affected

Our own answer: ranges merged, affected separated from platform-only, with confidence and review flags.

Morgan· Morgan Projectnpm
95%
v < 1.12.0
Affected range stops below 1.12.0, so it looks safe — our inference, not a vendor statement

Remediation

No guide yet

No remediation guidance has been written for this CVE yet. What the record does show:

Patch and advisory references

References (2)

Vendor Advisory
Source: cverecord
https://github.com/expressjs/morgan/security/advisories/GHSA-jxfw-x594-9x9m
Third Party Advisory
Source: cverecord
https://cna.openjsf.org/security-advisories.html

SSVC — Action Prioritization

SSVCNo known exploitAutomatablePartial impact

SSVC signals action urgency (what to patch first), separate from CVSS which measures severity.

CVSS

5.3MEDIUMopenjs
Vector?

Quick Info

StatusANALYZED
CWE
CWE-117

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