High [CVE-2026-66835] Erlang/OTP inets httpd: Directory protection bypass allows information disclosure
This high-severity Red Hat Linux advisory covers CVE-2026-66835 affecting Red Hat Hardened Images.
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Summary
Path Equivalence vulnerability in Erlang/OTP inets httpd allows a remote unauthenticated attacker to read files inside a mod_auth protected directory by prefixing the request path with an extra slash. httpd_request:validate_uri/1 normalises the request URI with uri_string:normalize/1, which performs RFC 3986 dot-segment removal but does not collapse empty path segments, so a doubled slash survives. mod_alias:real_name/3 concatenates the document root with that URI, and mod_auth:secret_path/3 then decides whether the result lies inside a protected directory block by running the configured directory path as an unanchored regular expression against it.
The doubled slash breaks the contiguous substring the regex needs, so the request is treated as unprotected and no authentication challenge is issued, while mod_get opens the same path and the operating system collapses the doubled slash and returns the protected file. The same path mismatch also evades the per-path accounting in mod_security.
This issue affects OTP from OTP 17.0 before OTP 27.3.4.17, from OTP 28.0 before OTP 28.5.0.6, and from OTP 29.0 before OTP 29.0.6, corresponding to inets from 5.10 before 9.3.2.7, from 9.4 before 9.6.2.3, and from 9.7 before 9.7.2.
Affected product named by the advisory: Red Hat Hardened Images.
- < 17.0
- < 27.3.4.17
- < 28.0
- < 28.5.0.6
- < 29.0
- < 29.0.6
- < 5.10
- < 9.3.2.7
- < 9.4
- < 9.6.2.3
- < 9.7
- < 9.7.2
Official advisory · high-confidence parse· fetched 12 days ago·verify at source
- erlang27-main-27.3.4.17-0.1.hum1
- RHSA-2026:62531
Official advisory · high-confidence parse· fetched 12 days ago·verify at source
Mitigation checklist
- To mitigate this issue, restrict network access to the Erlang/OTP inets httpd instance to trusted clients only. Alternatively, deploy a reverse proxy in front of the inets httpd that normalizes doubled slashes in request paths before forwarding, such as configuring nginx with its default merge_slashes directive. If inets httpd is not required, consider disabling the service. If the service is active, ensure that sensitive content is served through explicitly authenticated handlers rather than relying solely on mod_auth directory-block matching.
Official advisory · high-confidence parse· fetched 12 days ago·verify at source
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