ScriptAlias CGI targets bypass directory auth in inets httpd (mod_auth vs mod_cgi path mismatch)

Open Source Vulnerabilities CVE-2026-28808

Incorrect Authorization vulnerability in Erlang OTP (inets modules) allows unauthenticated access to CGI scripts protected by directory rules when served via script_alias. When script_alias maps a URL prefix to a directory outside DocumentRoot, mod_auth evaluates directory-based access controls against the DocumentRoot-relative path while mod_cgi executes the script at the ScriptAlias-resolved path. This path mismatch allows unauthenticated access to CGI scripts that directory rules were meant to protect. This vulnerability is associated with program files lib/inets/src/http_server/mod_alias.erl, lib/inets/src/http_server/mod_auth.erl, and lib/inets/src/http_server/mod_cgi.erl. This issue affects OTP from OTP 17.0 before OTP 28.4.2, OTP 27.3.4.10 and OTP 26.2.5.19, corresponding to inets from 5.10 before 9.6.2, 9.3.2.4 and 9.1.0.6.

Open Source Vulnerabilities EEF-CVE-2026-28808

## Summary Incorrect Authorization vulnerability in Erlang OTP (inets modules) allows unauthenticated access to CGI scripts protected by directory rules when served via script\_alias. When script\_alias maps a URL prefix to a directory outside DocumentRoot, mod\_auth evaluates directory-based access controls against the DocumentRoot-relative path while mod\_cgi executes the script at the ScriptAlias-resolved path. This path mismatch allows unauthenticated access to CGI scripts that directory rules were meant to protect. This vulnerability is associated with program files lib/inets/src/http\_server/mod\_alias.erl, lib/inets/src/http\_server/mod\_auth.erl, and lib/inets/src/http\_server/mod\_cgi.erl. This issue affects OTP from OTP 17.0 before OTP 28.4.2, OTP 27.3.4.10 and OTP 26.2.5.19, corresponding to inets from 5.10 before 9.6.2, 9.3.2.4 and 9.1.0.6. ## Workaround \* Move CGI scripts inside DocumentRoot and use alias instead of script\_alias to ensure mod\_auth resolves the correct path. \* Apply URL-based access controls at a reverse proxy layer to block unauthenticated access to the script\_alias URL prefix. \* Remove mod\_cgi from the httpd modules chain if CGI functionality is not required. ## Configuration The inets httpd server must use script\_alias to map a URL prefix to a CGI directory, combined with directory-based access controls (e.g., mod\_auth) protecting the script\_alias target path. The vulnerability applies whenever the script\_alias target path differs from DocumentRoot + URL prefix.