CVE-2025-35939
Craft CMS External Control of Assumed-Immutable Web Parameter Vulnerability
Craft CMS Craft CMS
Craft CMS stores arbitrary content provided by unauthenticated users in session files. This content could be accessed and executed, possibly using an independent vulnerability. Craft CMS redirects requests that require authentication to the login page and generates a session file on the server at '/var/lib/php/sessions'. Such session files are named 'sess_[session_value]', where '[session_value]' is provided to the client in a 'Set-Cookie' response header. Craft CMS stores the return URL requested by the client without sanitizing parameters. Consequently, an unauthenticated client can introduce arbitrary values, such as PHP code, to a known local file location on the server. Craft CMS versions 5.7.5 and 4.15.3 have been released to address this issue.
Exploitation status
CISA Known Exploited Vulnerabilities
Listed by CISA on 2 June 2025. US federal agencies were required to remediate it by 23 June 2025.
EPSS — exploitation probability
FIRST puts the probability of exploitation activity in the next 30 days at 1.4%, which is higher than 72.1% of all scored vulnerabilities. EPSS is a forecast of activity, not a measure of severity, and it is rescored daily.
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N
Frequently asked questions
Is CVE-2025-35939 being exploited by ransomware groups?
No ransomware group in this database is currently recorded as exploiting CVE-2025-35939.
What does CVE-2025-35939 affect?
CVE-2025-35939 affects Craft CMS Craft CMS. Craft CMS stores arbitrary content provided by unauthenticated users in session files. This content could be accessed and executed, possibly using an independent vulnerability. Craft CMS redirects requests that require authentication to the login page and generates a session file on the server at '/var/lib/php/sessions'. Such session files are named 'sess_[session_value]', where '[session_value]' is provided to the client in a 'Set-Cookie' response header. Craft CMS stores the return URL requested by the client without sanitizing parameters. Consequently, an unauthenticated client can introduce arbitrary values, such as PHP code, to a known local file location on the server. Craft CMS versions 5.7.5 and 4.15.3 have been released to address this issue.
How severe is CVE-2025-35939?
CVE-2025-35939 is rated MEDIUM with a CVSS base score of 5.3. EPSS puts the probability of exploitation in the next 30 days at 1.4%, higher than 72.1% of all scored vulnerabilities. It is listed in the CISA Known Exploited Vulnerabilities catalog, with a federal remediation deadline of 23 June 2025.
How should organisations respond to CVE-2025-35939?
Apply the vendor patch for Craft CMS Craft CMS as the first priority, and treat any internet-facing instance as the most urgent. Because this vulnerability is associated with ransomware activity, also review whether the affected systems were reachable before patching, rather than assuming that patching alone closes the incident.