CrushFTP Authentication Bypass
CVE-2025-31161 is a critical-severity authentication bypass by primary weakness vulnerability in CrushFTP, with a CVSS 3.1 base score of 9.8 out of 10. It can be exploited remotely over the network by an unauthenticated attacker, without any action from a user. The record lists versions 10.8.4, 11.3.1 as the first without the flaw, so updating CrushFTP to one of those releases or later removes the exposure. CISA added it to the Known Exploited Vulnerabilities catalogue on April 7, 2025, which means attacks have been observed in the wild, including in ransomware campaigns.
Attackers are already exploiting this vulnerability, according to CISA.
What to do
- Update CrushFTP to 10.8.4 or 11.3.1, whichever matches your release line, or a later version.
- CISA's 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.
- Read the advisory on crushftp.com for workarounds and exact fixed builds.
- Until you can update, restrict network access to the affected service so it is not reachable from untrusted networks.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| CrushFTP | CrushFTP | 10 up to, but not including, 10.8.4; 11 up to, but not including, 11.3.1 | 10.8.4, 11.3.1 |
Version data comes from the organisation that assigned the CVE. Confirm against the vendor advisory before deciding you are unaffected.
How the severity score breaks down
- Attack vector
- NetworkCan be exploited remotely over a network, including the internet.
- Attack complexity
- LowNo special conditions are needed; the attack works reliably.
- Privileges required
- NoneNo account or login is needed.
- User interaction
- NoneNo action by a victim is required.
- Scope
- UnchangedImpact stays within the vulnerable component.
- Confidentiality
- HighAll data handled by the component can be read.
- Integrity
- HighData or code can be modified at will.
- Availability
- HighThe component can be taken down completely.
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H. Scored by NVD.
| Scoring system | Score | Severity | Scored by |
|---|---|---|---|
| CVSS 3.1 | 9.8 | Critical | CNA (mitre.org) |
| CVSS 3.1 | 9.8 | Critical | NVD |
Official 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.
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: 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.
More Authentication Bypass by Primary Weakness vulnerabilities (CWE-305)
Timeline
- CVE record published.
- Added to CISA's Known Exploited Vulnerabilities catalogue.
- Deadline for US federal agencies to remediate, set by CISA.
- CISA published its SSVC assessment (exploitation: active, automatable: yes, technical impact: total).
- Record last changed materially (score, affected products, status or references).
References
Patches and release notes
- vicarius.io/vsociety/posts/cve-2025-31161-mitigate-crushftp-vulnerabilityMitigation, Third Party Advisory
Third-party and government advisories
- outpost24.com/blog/crushftp-auth-bypass-vulnerability/Third Party Advisory
- cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2025-31161US Government Resource
Technical write-ups (may include proof of concept)
- attackerkb.com/topics/k0EgiL9Psz/cve-2025-2825/rapid7-analysisExploit, Third Party Advisory
- projectdiscovery.io/blog/crushftp-authentication-bypassExploit, Third Party Advisory
- huntress.com/blog/crushftp-cve-2025-31161-auth-bypass-and-post-exploitationExploit, Third Party Advisory
- vicarius.io/vsociety/posts/cve-2025-31161-detect-crushftp-vulnerabilityExploit, Third Party Advisory
Other references
Other vulnerabilities in CrushFTP
- 9.8 Critical severity
CrushFTP Unprotected Alternate Channel Exploited
- 9.6 Critical severity
- 10.0 Critical severity
CrushFTP VFS Sandbox Escape Exploited
Recent Authentication Bypass by Primary Weakness vulnerabilities
- 8.1 High severity
- 8.1 High severity
- 9.1 Critical severity
- 7.1 High severity
- 8.1 High severity
- 7.8 High severity
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