CVE-2026-28808: ScriptAlias CGI targets bypass directory auth in inets httpd (mod_auth vs mod_cgi path mismatch)

Severity: critical (CVSS 9.8 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.6% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-04-07 · updated 2026-10-26
Weakness: CWE-863

Description

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 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.

Affected products

Erlang/Inets: from 5.10 before 9.1.0.6; from 9.2 (excl.) before 9.3.2.4; from 9.4 (excl.) before 9.6.2 — fixed in 9.1.0.6, 9.3.2.4, 9.6.2
Erlang OTP: from 17.0 before 26.2.5.19; from 27.0 before 27.3.4.10; from 28.0 before 28.4.2 — fixed in 26.2.5.19, 27.3.4.10, 28.4.2

How to fix

Upgrade to a fixed version: Erlang/Inets 9.1.0.6, 9.3.2.4, 9.6.2; Erlang OTP 26.2.5.19, 27.3.4.10, 28.4.2. Check the vendor advisory for mitigations.

References

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