CVE-2026-74994: inets, httpd: Authentication Bypass via Directory Namespace Collapse in httpd mod_auth
Summary
The modauth module in OTP's inets httpd server, when configured with dets or mnesia authentication backends and multiple directory configuration blocks, collapses all directory blocks into a single shared user/group namespace. A user added to one protected directory is accepted as valid for all other protected directories on the same server instance.
This issue affects OTP from OTP 17.0 before OTP 27.3.4.17, OTP 28.5.0.6, and OTP 29.0.6, corresponding to inets from 5.10 before 9.3.2.7, 9.6.2.3, and 9.7.2. Whether OTP before OTP 17.0, corresponding to inets before 5.10, is affected is unknown.
Other sources
inets, httpd: Authentication Bypass via Directory Namespace Collapse in httpd modauth
— Microsoft
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade to a fixed release to a version that resolves this vulnerability.
Fixed in 26.2.5.21-6 - Upgrade
Upgrade
debian/erlangto a version that resolves this vulnerability.Fixed in 1:27.3.4.1+dfsg-1+deb13u4 - Upgrade
Upgrade
debian/erlangto a version that resolves this vulnerability.Fixed in 1:29.0.6+dfsg-1 - Upgrade
Upgrade
debian/erlangto a version that resolves this vulnerability.Fixed in 1:27.3.4.1+dfsg-1+deb13u4Fixed in 1:29.1.2+dfsg-1 - Upgrade
Upgrade
Erlang/OTPto a version that resolves this vulnerability.Fixed in 27.3.4.17 - Upgrade
Upgrade
Erlang/OTPto a version that resolves this vulnerability.Fixed in 28.5.0.6 - Upgrade
Upgrade
Erlang/OTPto a version that resolves this vulnerability.Fixed in 29.0.6 - Upgrade
Upgrade
inetsto a version that resolves this vulnerability.Fixed in 9.3.2.7 - Upgrade
Upgrade
inetsto a version that resolves this vulnerability.Fixed in 9.6.2.3 - Upgrade
Upgrade
inetsto a version that resolves this vulnerability.Fixed in 9.7.2
Event History
Frequently Asked Questions
Which deployments are exposed to cross-directory authentication reuse?
Deployments using inets httpd mod_auth with a dets or mnesia authentication backend and multiple directory configuration blocks are exposed. The unintended user/group namespace sharing applies among protected directories on the same server instance.
What access would an attacker need to take advantage of this issue?
The attacker needs credentials for a user that has been added to one protected directory. Those credentials may then be accepted for other protected directories on the same server instance.
Which releases should be upgraded?
Upgrade OTP 17.x through 27.x to 27.3.4.17 or later, OTP 28.x to 28.5.0.6 or later, or OTP 29.x to 29.0.6 or later. The corresponding fixed inets versions are 9.3.2.7, 9.6.2.3, and 9.7.2, respectively.
How can I identify systems that need review?
Review systems running an affected OTP or inets version that use mod_auth with dets or mnesia and define more than one directory configuration block. OTP before 17.0, and inets before 5.10, have an unknown affected status.