---
title: "CVE-2025-35939: Craft CMS External Control of Assumed-Immutable Web Parameter Vulnerability"
url: https://erroneo.us/security/cve/CVE-2025-35939/
description: "CVE-2025-35939 (Craft CMS Craft CMS): Exploited in the wild (CISA KEV). Craft CMS stores arbitrary content provided by unauthenticated users in session…"
type: vulnerability-record
section: "Security Digest"
date_published: 2025-05-07
date_modified: 2026-02-26
publisher: erroneo.us
author: erroneo.us Security Desk
cve: "CVE-2025-35939"
kev: true
cvss: 6.9
epss: 0.01349
license: All rights reserved. Quote with attribution and a link.
---

# CVE-2025-35939: Craft CMS External Control of Assumed-Immutable Web Parameter Vulnerability

**Signal:** Exploited: patch now if you run it. CISA has confirmed exploitation in the wild. (Computed from CISA KEV, EPSS and CVSS; not an editorial verdict.)

## Should you act?

- Yes, if you run Craft CMS Craft CMS. CISA added this CVE to its Known Exploited Vulnerabilities catalog on 2025-06-02, which means there is reliable evidence of exploitation in the wild. US federal agencies must remediate by 2025-06-23 ; treat that as the outer limit, not the target.
- EPSS 1.3% , percentile 71: FIRST’s model estimates a 1.3% chance of exploitation activity in the next 30 days, higher than 71% of all scored CVEs (moderate). EPSS is a probability, not a verdict.
- Remotely reachable with no login and no user interaction. If the vulnerable service is exposed to the internet, prioritize it.

## What it is

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[sessionvalue]', where '[sessionvalue]' 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.

## Affected products (CVE record)

- Craft CMS: < 5.7.5, < 4.15.3

## Severity

- cisa-cg CVSS 3.1: 5.3 `CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N`
- cisa-cg CVSS 4.0: 6.9 `CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N`

## Exploitation

- CISA KEV: added 2025-06-02; federal due date 2025-06-23. Known ransomware use: Unknown.
- 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.
- CISA SSVC assessment: exploitation active , automatable yes , technical impact partial .
- FIRST EPSS (model of 2026-10-21): 1.35% probability of exploitation activity in the next 30 days; percentile 71.

## Sources

- [Listed in CISA KEV notes (github.com)](https://github.com/craftcms/cms/pull/17220)
- [CVE.org record CVE-2025-35939](https://www.cve.org/CVERecord?id=CVE-2025-35939)
- [NVD entry CVE-2025-35939](https://nvd.nist.gov/vuln/detail/CVE-2025-35939)
- [CISA Known Exploited Vulnerabilities catalog entry](https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2025-35939)
- [url](https://github.com/craftcms/cms/releases/tag/4.15.3)
- [url](https://github.com/craftcms/cms/releases/tag/5.7.5)
- [url](https://raw.githubusercontent.com/cisagov/CSAF/develop/csaf_files/IT/white/2025/va-25-147-01.json)

---
Source page: https://erroneo.us/security/cve/CVE-2025-35939/ · Security Digest: https://erroneo.us/security/ · More: https://erroneo.us/llms.txt