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Attackers have exploited CrushFTP authentication-bypass flaw CVE-2025-31161 by sending a specially crafted GET request that impersonates a known username, including the default crushadmin, without supplying a password. The forged request yields an authenticated session cookie that can then be reused in a follow-on POST request to carry out privileged actions on the server, such as creating a new user, and researchers noted that public proof-of-concept code is available and multiple threat actors have already abused the bug in the wild.
Detection guidance shows defenders can identify exploitation by correlating the initial bypass request, the subsequent privileged POST, and the server's success response across packets and flows. Netomize published PacketSmith Yara-X logic using track_state and flow_state to tie those stages together, giving security teams a way to hunt for successful compromise attempts rather than relying on single-request signatures alone.
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Netomize published detection engineering guidance showing PacketSmith Yara-X rules for identifying exploitation of CVE-2025-31161. The rules correlate the authentication-bypass request, follow-on POST request, and successful server response across packets and flows.
The Netomize article states that public proof-of-concept code is available for CVE-2025-31161 and that multiple threat actors have exploited the CrushFTP authentication-bypass flaw in the wild. The vulnerability can be abused with a crafted GET request and a reused forged session cookie to perform privileged actions such as creating a new user.
ExaTrack publicly described Butoflex, including its HTTP-triggered activation, RC4-decrypted second stage, persistence and reinfection methods, and timestomping behavior. The researchers also released YARA rules, hashes, and a network pattern to support threat hunting.
ExaTrack discovered a stealthy Linux passive backdoor named Butoflex during threat hunting on a compromised server. The malware had apparently remained undetected for more than 10 years and used ELF import modification to load a malicious library before legitimate ones.
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A critical CrushFTP authentication bypass flaw, initially tracked as `CVE-2025-2825` and later re-tracked as `CVE-2025-31161`, allows unauthenticated remote attackers to log in as valid users by sending a crafted S3-compatible `Authorization` header. The bug affects versions `10.0.0–10.8.3` and `11.0.0–11.3.0`, and stems from flawed authentication logic in `loginCheckHeaderAuth()` that can skip password verification when processing AWS4-HMAC-style credentials. Researchers reported that an attacker may need only a username in the `Credential` field and a syntactically valid `CrushAuth` cookie format, without successful signature validation, to gain unauthorized access. Security teams reported active exploitation against internet-exposed CrushFTP servers, with Shadowserver observing dozens of attack attempts in the wild. CrushFTP addressed the issue in `10.8.4` and `11.3.1`, including changes to properly validate passwords and a default-disabled setting to block the vulnerable path; defenders were urged to upgrade immediately, restrict external access, or enable DMZ mode where patching is not yet possible. ProjectDiscovery also released a Nuclei detection template that checks for successful user-list retrieval via the bypass, underscoring the need to identify exposed and vulnerable instances quickly.
Aug 15, 2026
A **critical CrushFTP zero-day**, tracked as `CVE-2025-54309`, has been reported as **actively exploited in the wild**, prompting urgent warnings from security researchers and national incident responders. The flaw affects **CrushFTP 11.x and 10.x** builds including **11.3.4_23 and later** and **10.8.5 and later**, and can allow attackers to **bypass authentication and obtain administrator access over HTTPS** when the **DMZ proxy service is disabled**. The issue has been assigned a **CVSS 3.1 score of 9.0** and has been linked to **improper AS2 validation** in vulnerable versions. CrushFTP released fixes in **11.3.4_26** and **10.8.5_12**, and defenders were urged to patch immediately or restore the application’s original configuration from **clean backups created on or before July 16** if patching is not yet possible. Reported indicators of compromise include changes to `MainUsers/default/user.xml` containing the string `last_logins`, creation of unknown administrator accounts with long identifiers, unusual UI behavior, administrator logins from unfamiliar IP addresses, and altered permissions on sensitive directories.
Jul 24, 2026
CrushFTP warned customers to patch an actively exploited zero-day, now tracked as **CVE-2024-4040**, that lets unauthenticated attackers escape the product’s virtual file system sandbox and download system files. The company said the flaw was reported and patched immediately, with fixes released in **CrushFTP v10.7.1** and **v11.1.0**; organizations still running **v9** were urged to upgrade to v11 or apply updates through the product dashboard. Airbus CERT also published a public scanner for the vulnerability on GitHub, underscoring rapid defender and researcher interest in identifying exposed systems. CrowdStrike said the bug was exploited in the wild in targeted attacks against multiple U.S. organizations and assessed the activity as an intelligence-gathering campaign that was likely politically motivated. CrushFTP added that deployments using a **DMZ** in front of the main instance were protected from the observed attacks, while internet exposure remained a major concern: Shodan data cited in reporting showed roughly **2,700** CrushFTP instances with their web interface accessible online, expanding the pool of potentially vulnerable targets.
Jun 29, 2026