# EPUBCheck RSC-026: URL leaks outside the EPUB, how to fix it

Source: https://epubcc.com/epubcheck/rsc-026/ (updated 2026-11-04)

EPUBCheck RSC-026 is an error message: “URL "…" leaks outside the container (it is not a valid-relative-ocf-URL-with-fragment string).” A relative URL climbs above the root of the EPUB (too many ../), pointing outside the container. Reading apps cannot follow it, so the link or resource is broken.

- Official message (EPUBCheck 5.4.0): URL "%1$s" leaks outside the container (it is not a valid-relative-ocf-URL-with-fragment string)
- Default severity: Error

## Typical causes

- A path written for the original folder structure that has one ../ too many.
- Files moved into a different folder depth without updating their relative links.

## How to fix it

1. Find the URL named in the message and the document that contains it.
2. Count the folders between the document and the target and correct the relative path so it stays inside the book.
3. Validate again.

## When it's not this

A path that stays inside the book but names a missing file is RSC-007.

## Sources

- EPUB 3.3, §4.2.5 URLs in the OCF abstract container: https://www.w3.org/TR/epub-33/#sec-container-iri (read 2026-11-04)

Message text and severity: EPUBCheck (W3C, BSD-3-Clause). Explanation: EpubCC.