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

Should you act?

Exploited: patch now if you run it

CISA has confirmed exploitation in the wild. This signal is computed from CISA KEV, EPSS and CVSS data; it is not an editorial verdict.

• 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.

CISA’s summary

Craft CMS contains an external control of assumed-immutable web parameter vulnerability. This vulnerability could allow an unauthenticated client to introduce arbitrary values, such as PHP code, to a known local file location on the server. This vulnerability could be chained with CVE-2024-58136 as represented by CVE-2025-32432.

Weakness type: CWE-472.

Product: Craft CMS Craft CMS · Assigned by: cisa-cg · Published: 2025-05-07

Affected and fixed versions

Severity scores

• Attack vector: network (remotely reachable)
• Attack complexity: low
• Attack requirements: none
• Privileges required: none (no login)
• User interaction: none

CVSS measures how bad a flaw is if exploited, not how likely exploitation is. Read it next to the exploitation data below.

Exploitation and urgency

• 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.

Timeline

• 2025-05-07 — CVE record published by cisa-cg
• 2025-06-02 — Added to CISA’s Known Exploited Vulnerabilities catalog
• 2025-06-23 — CISA remediation deadline for US federal agencies
• 2026-02-26 — CVE record last updated

Sources and references

Original sources first. Version and fix details should always be confirmed against the vendor or project advisory.

Vendor and project advisories, patches

1. Listed in CISA KEV notes (github.com) github.com

Vulnerability records

1. CVE.org record CVE-2025-35939 cve.org
2. NVD entry CVE-2025-35939 nvd.nist.gov

Government

1. CISA Known Exploited Vulnerabilities catalog entry cisa.gov

Other references from the CVE record and advisory

1. url github.com
2. url github.com
3. url raw.githubusercontent.com

All exploited Craft CMS vulnerabilities · Today’s Security Digest