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CVE-2026-15603 medium CVSS 5.3

Vulnerability in morgan (CVE-2026-15603)

Summary

Vulnerability in morgan (CVE-2026-15603). Risk of unauthorized operations or information disclosure. Exploitable via combined. Mitigation: upgrade to 1.12.0 or later.

Original description

The description as published by the source.

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 fix of CVE-2026-5078.

Patches

Users should upgrade to version 1.12.0.

Workarounds

None. The affected values include the request URL and request headers, which are core to access logging, so there is no practical format-based mitigation. Upgrade to 1.12.0.

Source: NIST National Vulnerability Database NVD GitHub Advisory

Auto-generated summary

Assembled by SecPulse from the source data (CVSS, CWE, affected versions) using templates — no AI involved. Check the original description and references below for exact details.

A vulnerability tracked as CVE-2026-15603 has been found in morgan.
Attackers can target a specific entry point like combined over the network to misuse the product.
Risk of unauthorized operations or information disclosure. CVSS score: 5.3/10.
What to do: upgrade morgan to 1.12.0 or later.
If unsure, ask your IT team or search "morgan CVE-2026-15603" on the vendor's site.

CVE-2026-15603 (morgan) — CWE-117 / CVSS v3 5.3
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Attack surface: combined / common / default / short
Patched: 1.12.0 — apply immediately
Workaround: None.
Plan: 1) Audit SBOM/dependencies, 2) Stage→prod upgrade, 3) Add WAF/proxy monitoring on affected endpoints, 4) Hunt IOCs in logs.
Refs: see the GHSA / vendor advisory / patched release linked on this page.

❓ What is the problem

A vulnerability (CWE-117) exists in morgan. Attackers reach the vulnerable code path via combined without authentication.

📍 Affected scope

Check the vendor advisory for the affected versions of morgan. Attack surface: combined / common / default / short.

🔥 Severity

Severity: Medium (CVSS 5.3/10). Risk of unauthorized operations or information disclosure.

🔧 How to fix

Update to 1.12.0.

🛡️ Workaround

Workaround: None.

🔍 Detection

Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Run grep -r 'morgan' . against your dependency files (package-lock.json, requirements.txt, go.sum) to find affected services.

Response actions

Concrete steps and command examples for SOC/SRE teams to execute in order

  1. 1
    Identify exposure identify 
    grep -r 'morgan' . | grep -v node_modules

    リポジトリと本番環境の依存ファイル (package-lock.json / requirements.txt / go.sum / Gemfile.lock 等) で morgan を grep し、稼働しているサービス・バージョンを把握する。

  2. 2
    Apply temporary workaround mitigate 
    None.

    パッチが適用されるまでの応急処置として、None. を実施。回避策の副作用 (機能低下) を確認した上で。

  3. 3
    Apply patch patch 
    Upgrade morgan to 1.12.0

    ステージング環境で 1.12.0 に上げて回帰テスト → 本番反映。回帰テストはアプリの主要ハッピーパスを含めること。

  4. 4
    Post-deployment verification verify 
    Confirm patched version is live in production

    パッチ適用後、ステージングで PoC または同等の悪用パターンを再現して脆弱性が閉じたことを確認。本番ではアクセスログ・WAF でアラート再発が無いか継続監視。

Affected packages

npm morgan
[{"type":"SEMVER","events":[{"introduced":"0"},{"fixed":"1.12.0"}]}]

Fix status by distribution

Fixed packages published by each distribution for this CVE

References

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