• If the password reset feature is enabled, an attacker can use a specially crafted host header to cause the password reset email to contain a link to a malicious site.

  Thanks to Nyein Chan Aung and Mg Demon for reporting this.

• If Webmin is configured to trust remote IP addresses provided by a proxy and you have users authenticating using client SSL certificates, a browser connecting directly (not via the proxy) can provide a forged header to fake the client certificate.

• Upgrade to Webmin 2.301 or later, and if there is any chance of direct requests by clients disable this at Webmin ⇾ Webmin Configuration ⇾ IP Access Control page using Trust level for proxy headers option.

  Thanks to Keigo YAMAZAKI from LAC Co., Ltd. for reporting this.

• A less-privileged Webmin user can execute commands as root via a vulnerability in the shell autocomplete feature.

• All Virtualmin admins and Webmin admins who have created additional accounts should upgrade to version 2.111 as soon as possible!

  Thanks to Trend Micro’s Zero Day Initiative for finding and reporting this issue.

• If a less-privileged Webmin user is given permission to edit the configuration of the HTTP Tunnel module, he/she could use this to introduce a vulnerability that captures cookies belonging to other Webmin users that use the module.

  Thanks to BLACK MENACE and PYBRO for reporting this issue.

• An HTML email crafted by an attacker could capture browser cookies when opened.

  Thanks to ly1g3 for reporting this bug.

• Less privileged Webmin users (excluding those created by Virtualmin and Cloudmin) can modify arbitrary files with root privileges, and so run commands as root. All systems with additional untrusted Webmin users should upgrade immediately.

  Thanks to esp0xdeadbeef and V1s3r1on for finding and reporting this issue!

• Less privileged Webmin users who do not have any File Manager module restrictions configured can access files with root privileges, if using the default Authentic theme. All systems with additional untrusted Webmin users should upgrade immediately. Note that Virtualmin systems are not effected by this bug, due to the way domain owner Webmin users are configured.

  Thanks to Faisal Fs (faisalfs10x) from NetbyteSEC for finding and reporting this issue!

• Version 1.0 of the procmail-wrapper package installed with Virtualmin has a vulnerability that can be used by anyone with SSH access to gain root privileges. To prevent this, all Virtualmin users should upgrade to version 1.1 or later immediately.

• If Webmin is installed using the non-recommended setup.pl script, checking for unknown referers is not enabled by default. This opens the system up to XSS and CSRF attacks using malicious links. Fortunately the standard rpm, deb, pkg and tar packages do not use this script and so are not vulnerable. If you did install using the setup.pl script, the vulnerability can be fixed by adding the line referers_none=1 to /etc/webmin/config file.

Thanks to Meshal ( Mesh3l_911 ) @Mesh3l_911 and Mohammed ( Z0ldyck ) @electronicbots for finding and reporting this issue!

• A user with privileges to create custom commands could exploit other users via unescaped HTML.

Thanks to Mauro Caseres for reporting this and the following issue.

• Saving a malicious HTML attachment could trigger and XSS vulnerability.

• Webmin releases between these versions contain a vulnerability that allows remote command execution! Version 1.890 is vulnerable in a default install and should be upgraded immediately - other versions are only vulnerable if changing of expired passwords is enabled, which is not the case by default.

  Either way, upgrading to version 1.930 is strongly recommended. Alternately, if running versions 1.900 to 1.920, edit /etc/webmin/miniserv.conf, remove the passwd_mode= line, then run /etc/webmin/restart command. {{< details-start post-indent-details "More details.." >}} Webmin version 1.890 was released with a backdoor that could allow anyone with knowledge of it to execute commands as root. Versions 1.900 to 1.920 also contained a backdoor using similar code, but it was not exploitable in a default Webmin install. Only if the admin had enabled the feature at Webmin ⇾ Webmin Configuration ⇾ Authentication to allow changing of expired passwords could it be used by an attacker.

  Neither of these were accidental bugs - rather, the Webmin source code had been maliciously modified to add a non-obvious vulnerability. It appears that this happened as follows :

  • At some time in April 2018, the Webmin development build server was exploited and a vulnerability added to the password_change.cgi script. Because the timestamp on the file was set back, it did not show up in any Git diffs. This was included in the Webmin 1.890 release.
  • The vulnerable file was reverted to the checked-in version from GitHub, but sometime in July 2018 the file was modified again by the attacker. However, this time the exploit was added to code that is only executed if changing of expired passwords is enabled. This was included in the Webmin 1.900 release.
  • On September 10th 2018, the vulnerable build server was decommissioned and replaced with a newly installed server running CentOS 7. However, the build directory containing the modified file was copied across from backups made on the original server.
  • On August 17th 2019, we were informed that a 0-day exploit that made use of the vulnerability had been released. In response, the exploit code was removed and Webmin version 1.930 created and released to all users.

  In order to prevent similar attacks in future, we're doing the following :

  • Updating the build process to use only checked-in code from GitHub, rather than a local directory that is kept in sync.
  • Rotated all passwords and keys accessible from the old build system.
  • Auditing all GitHub commits over the past year to look for commits that may have introduced similar vulnerabilities. {{< details-end >}}

• This is not a workable exploit as it requires that the attacker already know the root password. Hence there is no fix for it in Webmin.

• If the Upload and Download or File Manager module is used to fetch an un-trusted URL. If a Webmin user downloads a file from a malicious URL, HTTP headers returned can be used exploit an XSS vulnerability.

Thanks to independent security researcher, John Page aka hyp3rlinx, who reported this vulnerability to Beyond Security's SecuriTeam Secure Disclosure program.

• Only an issue if your system has un-trusted users with Webmin access and is using the new Authentic theme. A non-root Webmin user could use the theme configuration page to execute commands as root.

• Only if the Authentic theme is enabled globally. An attacker could execute commands remotely as root, as long as there was no firewall blocking access to Webmin's port 10000.

• A malicious website could create links or JavaScript referencing the xmlrpc.cgi script, triggered when a user logged into Webmin visits the attacking site.

Thanks to Peter Allor from IBM for finding and reporting this issue.

• If un-trusted users have both SSH access and the ability to use Read User Mail module (as is the case for Virtualmin domain owners), a malicious link could be created to allow reading any file on the system, even those owned by root.

Thanks to Patrick William from RACK911 labs for finding this bug.

• If your bash shell is vulnerable to shellshock, it can be exploited by attackers who have a Webmin login to run arbitrary commands as root. Updating to version 1.710 (or updating bash) will fix this issue.

• A malicious website could create links or JavaScript referencing the File Manager module that allowed execution of arbitrary commands via Webmin when the website is viewed by the victim. See CERT vulnerability note VU#788478 for more details. Thanks to Jared Allar from the American Information Security Group for reporting this problem.

• If an attacker has control over http://example.com/ then he/she could create a page with malicious JavaScript that could take over a Webmin session at https://example.com:10000/ when http://example.com/ is viewed by the victim.

Thanks to Marcin Teodorczyk for finding this issue.

• This vulnerability can be triggered if an attacker changes his Unix username via a tool like chfn, and a page listing usernames is then viewed by the root user in Webmin.

Thanks to Javier Bassi for reporting this bug.

• This bug allows a virtual server owner to read or write to arbitrary files on the system by creating malicious symbolic links and then having Virtualmin perform operations on those links. Upgrading to version 3.70 is strongly recommended if your system has un-trusted domain owners.

• This attack could open users who visit un-trusted websites while having Webmin open in the same browser up to having their session cookie captured, which could then allow an attacker to login to Webmin without a password. The quick fix is to go to the Webmin Configuration module, click on the Trusted Referers icon, set Referrer checking enabled? to Yes, and un-check the box Trust links from unknown referrers. Webmin 1.400 and Usermin 1.330 will make these settings the defaults.

• Any user logged into Webmin can execute any command using special URL parameters. This could be used by less-privileged Webmin users to raise their level of access.

Thanks for Keigo Yamazaki of Little eArth Corporation for finding this bug.

• A malicious link to Webmin pam_login.cgi script can be used to execute JavaScript within the Webmin server context, and perhaps steal session cookies.

• When using Webmin or Usermin to browse files on a system that were created by an attacker, a specially crafted filename could be used to inject arbitrary JavaScript into the browser.

• An attacker can view the source code of Webmin CGI and Perl programs using a specially crafted URL. Because the source code for Webmin is freely available, this issue should only be of concern to sites that have custom modules for which they want the source to remain hidden.

• The XSS bug makes use of a similar technique to craft a URL that can allow arbitrary JavaScript to be executed in the user's browser if a malicious link is clicked on.

Thanks for Keigo Yamazaki of Little eArth Corporation for finding this bug.

• An attacker without a login to Webmin can read the contents of any file on the server using a specially crafted URL. All users should upgrade to version 1.290 as soon as possible, or setup IP access control in Webmin.

Thanks to Kenny Chen for bringing this to my attention.

• If running Webmin on Windows, an attacker can remotely view the contents of any file on your system using a specially crafted URL. This does not affect other operating systems, but if you use Webmin on Windows you should upgrade to version 1.280 or later.

Thanks to Keigo Yamazaki of Little eArth Corporation for discovering this bug.

• When logging of failing login attempts via syslog is enabled, an attacker can crash and possibly take over the Webmin webserver, due to un-checked input being passed to Perl's syslog function. Upgrading to the latest release of Webmin is recommended.

Thanks to Jack at Dyad Security for reporting this problem to me.

• Affects systems when the option Support full PAM conversations? is enabled on the Webmin ⇾ Webmin Configuration ⇾ Authentication page. When this option is enabled in Webmin or Usermin, an attacker can gain remote access to Webmin without needing to supply a valid login or password. Fortunately this option is not enabled by default and is rarely used unless you have a PAM setup that requires more than just a username and password, but upgrading is advised anyway.
  

Thanks to Keigo Yamazaki of Little eArth Corporation and JPCERT/CC for discovering and notifying me of this bug.

• Prior Webmin and Usermin versions do not have password timeouts turned on by default, so an attacker can try every possible password for the root or admin user until he/she finds the correct one.
  The solution is to enable password timeouts, so that repeated attempts to login as the same user will become progressively slower. This can be done by following these steps :

  • Go to the Webmin Configuration module.
  • Click on the Authentication icon.
  • Select the Enable password timeouts button.
  • Click the Save button at the bottom of the page.

  This problem is also present in Usermin, and can be prevented by following the same steps in the Usermin Configuration module.

• When viewing HTML email, several potentially dangerous types of URLs can be passed through. This can be used to perform malicious actions like executing commands as the logged-in Usermin user.

• Even if a Webmin user does not have access to a module, he/she can still view it's Module Config page by entering a URL that calls config.cgi with the module name as a parameter.

• By sending a specially constructed password, an attacker can lock out other users if password timeouts are enabled.