CVE-2026-104890: Kunstmaan CMS: MediaBundle extension blacklist bypass allows authenticated administrators to upload executable PHP files leading to remote code execution
Advisory generated from the CVE record, CISA, Exploit Observer and VEDAS: what it is, whether it is exploited, who is affected, and how to fix and detect it.
Generated by VEDAS. Scores as of 2026-11-04 15:41 UTC. Rebuilt every few hours from cve-scores, CISA KEV and vedas-signatures. How this works and its limits.
What it is
Kunstmaan CMS is an open source content management system based on the Symfony framework. Prior to 7.3.2, src/Kunstmaan/MediaBundle/Helper/File/FileHandler.php performs the blacklisted_extensions check case-sensitively in FileHandler::getFilePath and lowercases the stored extension afterward. An authenticated backend user with media access can upload a mixed-case executable extension such as PHP that bypasses the check and is stored in the web-accessible media directory with an executable lowercase extension. The default blacklist also omits several server-executable extension types, allowing the same code-execution impact where the web server executes uploaded files. This issue is fixed in version 7.3.2.
Description quoted from the CVE record (assigned by GitHub_M, published 2026-10-05).
Weakness: CWE-434: Unrestricted Upload of File with Dangerous Type
How it can be exploited
Exploitable over the network with low attack complexity needing high privileges and no user interaction. Impact: confidentiality high, integrity high, availability high. CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:H
CISA assessment (SSVC): CISA has no evidence of exploitation. Automatable: no. Technical impact: total.
Public exploit evidence (Exploit Observer)
Exploit Observer found 3 code repositories naming this CVE.
Code repositories that name a CVE are often scanners, copies or fakes, and some are malware. Read the code before running anything.
See all 8 references on Exploit Observer
Live scores
- EPSS
- 0.004
low predicted chance of attack - VEDAS
- 0.986
strong exploit evidence - On CISA KEV
- Not listed
- Detection rule
- Suricata
Who is affected
| Product | Affected | Not affected |
|---|---|---|
| Kunstmaan KunstmaanBundlesCMS | version < 7.3.1 | Not stated |
| kunstmaan bundles-cms | version < 7.3.1 | Not stated |
| kunstmaan media-bundle | version < 7.3.1 | Not stated |
Version ranges exactly as the CVE record states them. “Before X” means X is the first fixed version.
How to fix it
No fixed version or vendor advisory is listed in the CVE record yet. Watch the vendor’s security page.
How to detect it
Suricata rules (network detection)
1 rule that alert on traffic matching this exploit: VEDAS CVE-2026-104890 Kunstmaan CMS - MediaBundle Arbitrary File Upload to RCE via Extension Bypass. Add them to your Suricata rule set and reload.
Show the rules
# CVE-2026-104890 - Kunstmaan CMS < 7.3.2 MediaBundle FileHandler::getFilePath() performs the
# blacklisted_extensions check case-sensitively and lowercases the stored extension afterward,
# so a mixed-case executable extension (e.g. .pHp) bypasses the filter and is stored executable
# in the web-accessible media directory (authenticated RCE). Detect a MediaBundle upload
# (create/drop/bulkuploadsubmit) whose filename carries a PHP/server-executable extension.
alert http $EXTERNAL_NET any -> $HTTP_SERVERS $HTTP_PORTS (msg:"VEDAS CVE-2026-104890 Kunstmaan CMS - MediaBundle Arbitrary File Upload to RCE via Extension Bypass"; flow:established,to_server; http.method; content:"POST"; http.uri; content:"media"; nocase; fast_pattern; pcre:"/media\/(?:create|drop|bulkupload)/i"; http.request_body; content:"filename="; nocase; pcre:"/filename=\x22?[^\x22\r\n]*\.(?:php[0-9]?|phtml|phtm|phar|pht|phps|phtm|shtml)\b/i"; classtype:web-application-attack; reference:cve,CVE-2026-104890; reference:url,https://www.exploit.observer/?keyword=CVE-2026-104890&match=exact; reference:url,https://subdomain.center/?engine=ammonites&keyword=kunstmaan&match=exact; sid:1101204; rev:1;)
CVE-2026-104890.rules on GitHub
References
Other references
- https://github.com/Kunstmaan/KunstmaanBundlesCMS/security/advisories/GHSA-p279-5wcv-45vq (x_refsource_CONFIRM)
- https://github.com/Kunstmaan/KunstmaanBundlesCMS/commit/1bbdfdeac8e7e91506b1a9271360b9b68d7690d3 (x_refsource_MISC)
- https://github.com/Kunstmaan/KunstmaanBundlesCMS/releases/tag/7.3.2 (x_refsource_MISC)
Other databases
Where this comes from
This advisory is generated automatically by VEDAS from: CVE.org record, cve-scores (EPSS and VEDAS), Exploit Observer, vedas-signatures. Text in quotes is reproduced from the source; everything else is a fixed template filled with source fields. Nothing here is written by a language model. Check the vendor advisory before acting, and read how VEDAS and Exploit Observer work, and their limits.
Supporting partners
