{"id":"CVE-2026-15603","aliases":["GHSA-jxfw-x594-9x9m"],"title":"morgan vulnerable to Log Forging via unescaped Unicode line separators","summary":"morgan vulnerable to Log Forging via unescaped Unicode line separators","severity":"medium","cvss":5.3,"cwe":["CWE-117"],"vendor":"morgan","product":"morgan","ecosystem":"npm","affected":["morgan < 1.12.0"],"patched":["morgan 1.12.0"],"published":"2026-09-08","updated":"2026-09-08","sourceUpdated":"2026-09-08T21:28:26Z","source":"GHSA","sourceUrl":"https://github.com/advisories/GHSA-jxfw-x594-9x9m","references":[{"url":"https://github.com/expressjs/morgan/security/advisories/GHSA-jxfw-x594-9x9m"},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-15603"},{"url":"https://github.com/expressjs/morgan/commit/fbf93833186920cc39bb19b247e4a86b61bef4fe"},{"url":"https://cna.openjsf.org/security-advisories.html"},{"url":"https://github.com/expressjs/morgan/releases/tag/1.12.0"},{"url":"https://github.com/advisories/GHSA-jxfw-x594-9x9m"}],"tags":["ghsa","npm"],"epss":0.00294,"epssPercentile":0.1962,"ingestedAt":"2026-09-08T22:12:30.968Z","slug":"CVE-2026-15603","body":"## Overview\n\n### Impact\n\nMorgan 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.\n\nWhen 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.\n\n### Patches\n\nUsers should upgrade to version 1.12.0.\n\n### Workarounds\n\nNone. 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.\n\n## Affected packages\n\n- `morgan < 1.12.0`\n\n## Remediation\n\nUpgrade to a patched release:\n\n- `morgan 1.12.0`","depth":"sunlit","depthScore":29,"depthScoreParts":{"impact":29.2,"likelihood":0.1,"exploitation":0,"ransomware":0},"changes":[]}