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Deep analysis by US confirm, that using CVE-2026-33691, in any
platform wheter windows or linux or mac, you can bypass unpatched CRS
and use CVE-2015-10138

as confirmed, as we see in that line

```
   1   // Lines 493-498 of public/includes/UploadHandler.php
   2   protected function trim_file_name($name, $type = null, $index =
null, $content_range = null) {
   3       // Remove path information and dots around the filename...
   4       // Also remove control characters and spaces (\x00..\x20)
around the filename:
   5       $name = trim(basename(stripslashes($name)), ".\x00..\x20");
   6       // ...
   7   }
```

It unlocks the old CVE-2015-10138 and an attacker get RCE if WAFs are
not patched, that unlocks the old vuln power against a modern WAF,
most peoples rely only on the WAF alone and `Work The Flow File
Upload` plugin is never patched and even run **EOL** that is very
common, That is the danger, after that confirm, we see one wordpress
plugin confirmed trims whitespaces from uploaded files

On Sun, Mar 29, 2026 at 3:33 AM cyber security <cs7778503 () gmail com> wrote:

A vulnerability was identified in OWASP CRS where whitespace padding
in filenames can bypass file upload extension checks, allowing uploads
of dangerous files such as .php, .phar, .jsp, and .jspx. This issue
has been assigned CVE‑2026‑33691.

Impact: Attackers may evade CRS protections and upload web shells
disguised with whitespace‑padded extensions. Exploitation is most
practical on Windows backends that normalize whitespace in filenames
before execution, In linux harder because it require a backend that
use like `.strip()` and `.trim()` and other whitespace trimming
methods depending on the language here vulnerable to that or the
webserver strip whitespaces or the backend on general, If not they not
vulnerable to that.

Fix: Patched in CRS v3.3.9, v4.25.x LTS, and v4.8.x. Security fixes
are always backported to supported branches.

References:

Full advisory: https://github.com/coreruleset/coreruleset/security/advisories/GHSA-rw5f-9w43-gv2w

Credits: Reported by RelunSec (aka @HackingRepo on Github).

Current thread:

• Re: [CVE-2026-33691] OWASP CRS whitespace padding bypass vulnerability cyber security (Apr 16)