Webmin: Users file injection in certificate handling leads to root access
Summary
Webmin through version 2.670 contains a users file injection vulnerability in the certificate issuing script acl/cert_issue.cgi. An authenticated Webmin user can supply certificate DN fields containing newlines, which adds a second root entry with a known password hash to the users file. After the miniserv service restarts, the attacker can gain Webmin root access.
Affected
- Webmin up to and including 2.670 (per the CVE record and aggregators)
Fixed in
- Unknown. The fix commits are referenced, but no confirmed fixed release is known. Do not assume 2.671 fixes this issue.
Workaround
- Restrict Webmin accounts to trusted administrators only.
- Restrict access to the Webmin port to a management VPN or allowlisted IP addresses.
- Do not expose Webmin to the internet.
Exploitation
- Not known to be exploited as of 11 Nov 2026.
- No public proof of concept found; this is not confirmed absent.
- Exploitation requires valid low-privilege Webmin credentials (PR:L).
Our recommendation
- Check which systems run Webmin and whether they are reachable from the internet; restrict access immediately.
- Limit Webmin accounts to the few administrators who need them and remove unused accounts.
- Review the Webmin users file for unexpected entries and alert on changes to it.
- Install the first fixed Webmin release as soon as the vendor confirms it; check the Webmin security page for updates.
Public exploits
PoC-in-GitHub, Metasploit and Exploit-DB list nothing for this CVE.
Research sources
- VulnCheck advisory www.vulncheck.com
- Fix commit 0c449e34 github.com
- Commit 8fb194e5 github.com
- cert_issue.cgi at 2.670 github.com
- CVE-2026-126781 aggregator record cve.threatint.com
- CVE-2026-126781 radar entry radar.offseq.com
Researched and written up in English and German by an AI (Claude by Anthropic) based on NVD, CISA, EPSS and the sources listed. The vendor information is authoritative. Researched on 11 Nov 2026, 20:31.
Original description (NVD)
Webmin through 2.670 contains a users file injection vulnerability in acl/cert_issue.cgi that allows authenticated Webmin users to inject lines by supplying unvalidated certificate DN fields containing newlines. Attackers can end a DN field with a backslash and newline to add a second root entry with a known password hash, gaining Webmin root access after miniserv restarts.
NVD references (4)
- https://github.com/webmin/webmin/blob/2.670/acl/cert_issue.cgi#L22-L52
- https://github.com/webmin/webmin/commit/0c449e341746d8c445c8c7db223eac1f41755943
- https://github.com/webmin/webmin/commit/8fb194e5fbc30a6664545d48940d03759ace9bf2
- https://www.vulncheck.com/advisories/webmin-through-2.670-users-file-injection-via-acl-cert-issue-cgi
Sources
The tracker combines official, freely usable data sources – updated continuously:
- NVD (NIST) – CVEs, rating (CVSS), affected products
- CISA KEV – vulnerabilities confirmed by CISA as actively exploited
- CISA Vulnrichment – CISA assessment (SSVC) in the official CVE record
- FIRST EPSS – probability of exploitation
- Microsoft MSRC – Patch Tuesday: vulnerabilities, severity, updates
- PoC-in-GitHub – public proof-of-concept repositories
- Metasploit (Rapid7) – modules of the Metasploit Framework
- Exploit-DB (OffSec) – archive of public exploits (links only)
- Patch days: official vendor pages (linked per vendor) (Vendor patch days)
This product uses data from the NVD API but is not endorsed or certified by the NVD. EPSS data © FIRST.org.
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