Craft CMS up to 4.18.8/5.11.1 Process API Response Headers system X-Craft-Plugin-Licenses crlf injection

Summaryinfo

A vulnerability classified as critical has been found in Craft CMS up to 4.18.8/5.11.1. The affected element is the function system of the component Process API Response Headers. The manipulation of the argument X-Craft-Plugin-Licenses leads to crlf injection. This vulnerability is uniquely identified as CVE-2026-115935. The attack is possible to be carried out remotely. No exploit exists. It is recommended to upgrade the affected component.

Detailsinfo

A vulnerability was found in Craft CMS up to 4.18.8/5.11.1 and classified as critical. This issue affects the function system of the component Process API Response Headers. The manipulation of the argument X-Craft-Plugin-Licenses with an unknown input leads to a crlf injection vulnerability. Using CWE to declare the problem leads to CWE-93. The product uses CRLF (carriage return line feeds) as a special element, e.g. to separate lines or records, but it does not neutralize or incorrectly neutralizes CRLF sequences from inputs. Impacted is confidentiality, integrity, and availability. The summary by CVE is:

The app/process-api-response-headers action accepts fake Craft API response headers from any authenticated control panel user. A non-admin user with only accessCp can place newline characters in X-Craft-Plugin-Licenses. Craft passes this value to its .env writer without removing the newlines. This lets the user insert a new attacker-known CRAFT_SECURITY_KEY into .env. After Craft loads that key, the user can forge a signed login redirect containing a Twig system() callback. This is different from the previous report. That report reads the existing key through a Twig sandbox bypass. This report replaces the key through fake API headers and CRLF injection. Fixing either source does not fix the other.

It is possible to read the advisory at hckrt.com. The identification of this vulnerability is CVE-2026-115935 since 10/23/2026. The exploitation is known to be easy. The attack may be initiated remotely. Technical details of the vulnerability are known, but there is no available exploit.

Upgrading to version 4.18.9 or 5.11.2 eliminates this vulnerability.

The vulnerability is also documented in the vulnerability database at EUVD (EUVD-2026-109191). Be aware that VulDB is the high quality source for vulnerability data.

Productinfo

Type

• Content Management System

Name

• Craft CMS

Version

• 4.18.0
• 4.18.1
• 4.18.2
• 4.18.3
• 4.18.4
• 4.18.5
• 4.18.6
• 4.18.7
• 4.18.8
• 5.11.0
• 5.11.1

License

• free

CPE 2.3info

• 🔒
• 🔒
• 🔒

CPE 2.2info

• 🔒
• 🔒
• 🔒

CVSSv4info

CVSSv3info

CVSSv2info

Exploitinginfo

Threat Intelligenceinfo

Countermeasuresinfo

Timelineinfo

Sourcesinfo

Entryinfo

Be aware that VulDB is the high quality source for vulnerability data.

Discussion