CVE-2026-28808: ScriptAlias CGI targets bypass directory auth in inets httpd (mod_auth vs mod_cgi path mismatch)
Incorrect Authorization vulnerability in Erlang OTP (inets modules) allows unauthenticated access to CGI scripts protected by directory rules when served via scriptalias.
When scriptalias maps a URL prefix to a directory outside DocumentRoot, modauth evaluates directory-based access controls against the DocumentRoot-relative path while modcgi 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/httpserver/modalias.erl, lib/inets/src/httpserver/modauth.erl, and lib/inets/src/httpserver/modcgi.erl.
This issue affects OTP from OTP 17.0 before OTP 26.2.5.19, OTP 27.3.4.10, and OTP 28.4.2, corresponding to inets from 5.10 before 9.1.0.6, 9.3.2.4, and 9.6.2. Whether OTP before OTP 17.0, corresponding to inets before 5.10, is affected is unknown.
Other sources
Incorrect Authorization vulnerability in Erlang OTP (inets modules) allows unauthenticated access to CGI scripts protected by directory rules when served via scriptalias.
When scriptalias maps a URL prefix to a directory outside DocumentRoot, modauth evaluates directory-based access controls against the DocumentRoot-relative path while modcgi 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/httpserver/modalias.erl, lib/inets/src/httpserver/modauth.erl, and lib/inets/src/httpserver/modcgi.erl.
This issue affects OTP from OTP 17.0 until OTP 28.4.2, 27.3.4.10 and 26.2.5.19 corresponding to inets from 5.10 until 9.6.2, 9.3.2.4 and 9.1.0.6.
— Red Hat
ScriptAlias CGI targets bypass directory auth in inets httpd (modauth vs modcgi path mismatch)
— Microsoft
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade
Erlang OTP (inets modules)to a version that resolves this vulnerability.Fixed in 28.4.2 - Upgrade
Upgrade
Erlang OTP (inets modules)to a version that resolves this vulnerability.Fixed in 27.3.4.10 - Upgrade
Upgrade
Erlang OTP (inets modules)to a version that resolves this vulnerability.Fixed in 26.2.5.19 - Upgrade
Upgrade
inets (mod_alias/mod_auth/mod_cgi)to a version that resolves this vulnerability.Fixed in 9.6.2 - Upgrade
Upgrade
inets (mod_alias/mod_auth/mod_cgi)to a version that resolves this vulnerability.Fixed in 9.3.2.4 - Upgrade
Upgrade
inets (mod_alias/mod_auth/mod_cgi)to a version that resolves this vulnerability.Fixed in 9.1.0.6 - Configuration
Mitigate the auth bypass caused by the directory-path mismatch: configure script_alias so that the URL prefix does not resolve to a directory outside DocumentRoot (so directory-based access controls and CGI execution evaluate the same path).
inets httpd (mod_auth / mod_cgi via mod_alias for script_alias) script_alias mapping (URL prefix -> filesystem directory) = Ensure ScriptAlias URL prefix does not map outside DocumentRoot (avoid mapping to a directory outside DocumentRoot)
Event History
Frequently Asked Questions
What is the severity of CVE-2026-28808?
CVE-2026-28808 is categorized with a medium severity due to incorrect authorization vulnerabilities allowing unauthenticated access.
How do I fix CVE-2026-28808?
To fix CVE-2026-28808, ensure to update affected Erlang OTP and inets software to the latest versions that address the vulnerability.
What versions of Erlang OTP are affected by CVE-2026-28808?
CVE-2026-28808 affects Erlang OTP versions from 17.0 to 28.4.2 inclusive.
What versions of Erlang inets are impacted by CVE-2026-28808?
This vulnerability affects Erlang inets versions between 5.10 and 9.6.2 inclusive, specifically those in the specified version ranges.
What type of vulnerability is CVE-2026-28808?
CVE-2026-28808 is an incorrect authorization vulnerability that allows access to protected CGI scripts.