Indexing of HTML CE with relative file path in iframe leads to exception in BE

[medarob]

The following iframe was integrated in a HTML CE:

<iframe class="sc-frame" height="800" src="../../../fileadmin/user_upload/WebGL_high/index_en.html" style="border:none"> 
   <a href="../../../fileadmin/user_upload/WebGL_high/index_en.html">Test</a> 
</iframe>

During the indexing process, which was started in the BE manually, this exception appears at some point:

Core: Exception handler (WEB): Uncaught TYPO3 Exception: #1320286857: File ../fileadmin/user_upload/WebGL_high/index_en.html is not valid (".." and "//" is not allowed in path). | TYPO3\CMS\Core\Resource\Exception\InvalidPathException thrown in file /var/www/typo3/public/typo3/sysext/core/Classes/Resource/Driver/AbstractHierarchicalFilesystemDriver.php in line 53. Requested URL: https://domain.tld/typo3/index.php?route=%%2Fmodule%%2Fweb%%2FKeSearchBackendModule&token=--AnonymizedToken--&id=217&do=startindexer

If an absolute path is used, the indexer finishes without exception.

[medarob]

We just tested this with v3.8.1 and the problem still exists here. The log file has the following entries:

Tue, 13 Jul 2021 03:15:40 +0200 [ERROR] request="1b86d92961a13" component="TeaminmediasPluswerk.KeSearch.Indexer.IndexerRunner": File ../fileadmin/user_upload/WebGL_high/index_en.html is not valid (".." and "//" is not allowed in path). Wed, 14 Jul 2021 03:15:39 +0200 [ERROR] request="d20a1768e3aa8" component="TeaminmediasPluswerk.KeSearch.Indexer.IndexerRunner": File ../fileadmin/user_upload/WebGL_high/index_en.html is not valid (".." and "//" is not allowed in path). Wed, 14 Jul 2021 10:26:28 +0200 [ERROR] request="6d35a684164c6" component="TeaminmediasPluswerk.KeSearch.Indexer.IndexerRunner": File ../fileadmin/user_upload/WebGL_high/index_en.html is not valid (".." and "//" is not allowed in path).