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CVE-2025-31161: CrushFTP Authentication Bypass Vulnerability
CVE-2025-31161 is rated critical with a CVSS v3.1 base score of 9.8 and affects CrushFTP CrushFTP. Per its scoring, it can be exploited over the network, without authentication, without any user interaction. The scored impact on confidentiality, integrity and availability is the highest available. CISA added it to its Known Exploited Vulnerabilities catalog on 2025-04-07, which means exploitation in the wild has been observed.
Vulnerability description
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 login_user_pass() 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.
Severity breakdown
CVSS v3.1 9.8: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
- Attack vector: Network. Exploitable remotely over the network, with no need for local or physical access.
- Attack complexity: Low. No special conditions; the attack can be repeated reliably.
- Privileges required: None. No account or prior access is needed.
- User interaction: None. No action from any user is needed.
- Scope: Unchanged. Impact stays within the vulnerable component.
- Confidentiality impact: High. Total loss of confidentiality; sensitive data can be fully disclosed.
- Integrity impact: High. Total loss of integrity; data or system state can be fully modified.
- Availability impact: High. Total loss of availability; the component can be shut down.
Underlying weakness
CWE-305: Authentication Bypass by Primary Weakness
The authentication algorithm is sound, but the implemented mechanism can be bypassed as the result of a separate weakness that is primary to the authentication error.
Affected products
- Crushftp: from 10.0.0 before 10.8.4; from 11.0.0 before 11.3.1
References
- https://crushftp.com/crush11wiki/Wiki.jsp?page=Update#section-Update-VulnerabilityInfo
- https://www.vicarius.io/vsociety/posts/cve-2025-31161-mitigate-crushftp-vulnerability
- https://outpost24.com/blog/crushftp-auth-bypass-vulnerability/
- https://attackerkb.com/topics/k0EgiL9Psz/cve-2025-2825/rapid7-analysis
- https://projectdiscovery.io/blog/crushftp-authentication-bypass
- https://www.huntress.com/blog/crushftp-cve-2025-31161-auth-bypass-and-post-exploitation
- https://www.vicarius.io/vsociety/posts/cve-2025-31161-detect-crushftp-vulnerability
- https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2025-31161
- https://www.darkreading.com/vulnerabilities-threats/disclosure-drama-clouds-crushftp-vulnerability-exploitation
- https://www.infosecurity-magazine.com/news/crushftp-flaw-exploited-disclosure/