Craft CMS External Control of Assumed-Immutable Web Parameter Vulnerability
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.
5.3
1.2%
Vector breakdown
- Attack vector
- Network
- Attack complexity
- Low
- Privileges required
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- None
- Integrity
- Low
- Availability
- None
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N
- Published
- May 7, 2025
- Modified
- Feb 26, 2026
- Added to KEV
- Jun 2, 2025
- Federal patch due
- Jun 23, 2025
CISA required action
Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.
Weakness classification
Proof-of-concept & exploitation references
Weaponization
Public repositories whose name or description references CVE-2025-35939, found via a live GitHub search at request time. These are community-sourced signals, not a verified working exploit - cross-check each one before relying on it, and treat higher star counts and recent activity as (weak) corroboration, not proof.
No public GitHub repositories referencing CVE-2025-35939 were found at last check. Absence here is not proof no exploit exists - see the references below for vendor advisories and write-ups.
References
Frequently asked questions
What is CVE-2025-35939?
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 has a CVSS base score of 5.3 out of 10 (CVSS 3.1).
Is CVE-2025-35939 actively exploited in the wild?
Yes. CVE-2025-35939 is listed in the CISA Known Exploited Vulnerabilities (KEV) catalog, added Jun 2, 2025, meaning CISA has confirmed evidence of active exploitation.
What is the EPSS score for CVE-2025-35939?
1.2% - meaning FIRST.org's EPSS model estimates a 1.2% probability this vulnerability will be exploited in the wild within 30 days (64% percentile among all scored CVEs).
What type of vulnerability is CVE-2025-35939?
CVE-2025-35939 is classified under CWE-472 (CWE-472 External Control of Assumed-Immutable Web Parameter).
Cross-checked against
Impactr finds and proves whether CVE-2025-35939 - or flaws like it - are actually reachable in your own web apps and APIs, with a reproducible exploit as evidence.
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