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

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

01What is this vulnerability?

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]'…

02Affected products

Vendor	Product	Versions
Craft	CMS	0, 5.7.5, 0, 4.15.3

03Active exploitation status

Yes — actively exploited. Added to the CISA KEV catalog on 2025-06-02. Ransomware use: Unknown.

04Recommended remediation

• Patch to a fixed version listed in the vendor advisory (see references below).
• Mitigate with WAF rules, network egress filters, or feature flags where the patch is not yet available.
• Hunt historical logs for exploitation indicators — see Detection signatures below.

05Technical details

For the full vendor write-up, exploit chains, and reference implementations, see the references list in section 09.

06Detection signatures

Open the Sigma generator with a pre-filled prompt for this CVE to draft a starting detection in your stack of choice:

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07Related CVEs

No directly-cited follow-up CVEs in the KB record for this advisory. The references list in section 09 carries the vendor cross-references.

08Timeline

• Published: 2025-05-07T22:41:29.728Z
• Last modified: 2026-02-26T18:28:42.701Z
• Added to CISA KEV: 2025-06-02
• BOD 22-01 due: 2025-06-23

09References

• github.com — https://github.com/craftcms/cms/pull/17220
• github.com — https://github.com/craftcms/cms/releases/tag/4.15.3
• github.com — https://github.com/craftcms/cms/releases/tag/5.7.5
• www.cve.org — https://www.cve.org/CVERecord?id=CVE-2025-35939
• raw.githubusercontent.com — https://raw.githubusercontent.com/cisagov/CSAF/develop/csaf_files/IT/white/2025/…