CVE-2025-31161: CrushFTP Authentication Bypass 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 CrushFTP CrushFTP. CISA added this CVE to its Known Exploited Vulnerabilities catalog on 2025-04-07, which means there is reliable evidence of exploitation in the wild. US federal agencies must remediate by 2025-04-28; treat that as the outer limit, not the target. CISA also lists it as known to be used in ransomware campaigns.
• EPSS 100.0%, percentile 100.0: FIRST’s model estimates a 100.0% chance of exploitation activity in the next 30 days, higher than 100.0% of all scored CVEs (very high). 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.
• Editorial verdict: Check exposure. CrushFTP Auth Bypass CVE-2025-31161 Exploited in the Wild — Fixed since March 2025 and widely exploited from early April; if you run CrushFTP, make sure you are on a current build (later CrushFTP flaws raised the minimum) and audit for backdoor admin accounts.

What it is

CrushFTP 10 before 10.8.4 and 11 before 11.3.1 allows authentication bypass and takeover of the crushadmin account (unless a DMZ proxy instance is used), as exploited in the wild in March and April 2025, aka "Unauthenticated HTTP(S) port access." A race condition exists in the AWS4-HMAC (compatible with S3) authorization method of the HTTP component of the FTP server. The server first verifies the existence of the user by performing a call to loginuserpass() with no password requirement. This will authenticate the session through the HMAC verification process and up until the server checks for user verification once more. The vulnerability can be further stabilized, eliminating the need for successfully triggering a race condition, by sending a mangled AWS4-HMAC header. By providing only the username and a following slash (/), the server will successfully find a username, which triggers the successful anypass authentication process, but the server will fail to find the expected SignedHeaders entry, resulting in an index-out-of-bounds error that stops the code from reaching the session cleanup. Together, these issues make it trivial to authenticate as any known or guessable user (e.g., crushadmin), and can lead to a full compromise of the system by obtaining an administrative account.

CISA’s summary

CrushFTP contains an authentication bypass vulnerability in the HTTP authorization header that allows a remote unauthenticated attacker to authenticate to any known or guessable user account (e.g., crushadmin), potentially leading to a full compromise.

Weakness type: CWE-305.

Product: CrushFTP CrushFTP · Assigned by: mitre · Published: 2025-04-03

Affected and fixed versions

Severity scores

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

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 2025-04-07; federal due date 2025-04-28. Known ransomware use: Known.
• 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 total.
• FIRST EPSS (model of 2026-10-21): 99.97% probability of exploitation activity in the next 30 days; percentile 100.0.

Timeline

• 2025-03-21 — erroneo.us brief: CrushFTP Auth Bypass CVE-2025-31161 Exploited in the Wild
• 2025-04-03 — CVE record published by mitre
• 2025-04-07 — Added to CISA’s Known Exploited Vulnerabilities catalog
• 2025-04-28 — CISA remediation deadline for US federal agencies
• 2025-10-21 — 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 (crushftp.com) crushftp.com

Vulnerability records

1. CVE.org record CVE-2025-31161 cve.org
2. NVD entry CVE-2025-31161 nvd.nist.gov

Government

1. CISA Known Exploited Vulnerabilities catalog entry cisa.gov

Other references from the CVE record and advisory

1. outpost24.com outpost24.com
2. crushftp.com crushftp.com
3. projectdiscovery.io projectdiscovery.io
4. darkreading.com darkreading.com
5. huntress.com huntress.com
6. attackerkb.com attackerkb.com
7. infosecurity-magazine.com infosecurity-magazine.com
8. vicarius.io vicarius.io
9. vicarius.io vicarius.io

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