The Crayons plugin for SPIP before 3.5.0 contains a missing authorization vulnerability that allows…

Why it is Amber

• CVSS 9.8 critical
• Remotely exploitable without logging in

References

• https://blog.spip.net/Mises-a-jour-de-securite-critique-plugins-Crayons-et-Simplog.html?lang=fr
• https://plugins.spip.net/crayons.html?lang=fr
• https://www.vulncheck.com/advisories/spip-crayons-plugin-authorization-bypass-rce

Original description

The Crayons plugin for SPIP before 3.5.0 contains a missing authorization vulnerability that allows unauthenticated attackers to modify arbitrary editable object fields by omitting the secu_ anti-forgery parameter in crayons_store.php, causing the authorization dispatcher to resolve an unconditionally-true handler instead of the proper modification check. Attackers can chain this flaw to write a malicious .html skeleton file, disclose sensitive configuration files containing the site secret, and forge a signed ajax context to execute the uploaded skeleton, achieving arbitrary PHP code execution as the web-server user.