CVE-2026-5078 – morgan vulnerable to Log Forging via unneutralized control characters in :remote-user

CVE ID :CVE-2026-5078

Published : June 3, 2026, 8:16 a.m. | 16 minutes ago

Description :Impact: The morgan logging middleware’s :remote-user token extracts the Basic auth username from the Authorization request header and writes it to the log stream without neutralizing control characters. An unauthenticated attacker can send a crafted Authorization Basic header containing CR or LF bytes to inject forged log lines, breaking the one-request-per-line structure of access logs and enabling log forgery against downstream log consumers. The built-in combined, common, default, and short formats are affected, as well as any custom format that references :remote-user. Affected versions: morgan 1.2.0 through 1.10.1. Patches: upgrade to morgan 1.11.0, which neutralizes control characters in the :remote-user token output. Workarounds: use a custom format string that does not include :remote-user.

Severity: 5.3 | MEDIUM

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