Impact

A bug in on-headers versions < 1.1.0 may result in response headers being inadvertently modified when an array is passed to response.writeHead()

Patches

Users should upgrade to 1.1.0

Workarounds

Uses are encouraged to upgrade to 1.1.0, but this issue can be worked around by passing an object to response.writeHead() rather than an array.

• https://github.com/jshttp/on-headers/security/advisories/GHSA-76c9-3jph-rj3q
• https://nvd.nist.gov/vuln/detail/CVE-2025-7339
• https://github.com/expressjs/morgan/issues/315
• https://github.com/jshttp/on-headers/issues/15
• https://github.com/jshttp/on-headers/commit/c6e384908c9c6127d18831d16ab0bd96e1231867
• https://cna.openjsf.org/security-advisories.html
• https://github.com/advisories/GHSA-76c9-3jph-rj3q