Erlang OTP httpd httpd_request:validate_uri path traversal

Summaryinfo

A vulnerability classified as problematic has been found in Erlang OTP. This vulnerability affects the function httpd_request:validate_uri of the component httpd. The manipulation leads to path traversal. This vulnerability is uniquely identified as CVE-2026-66835. The attack is possible to be carried out remotely. No exploit exists.

Detailsinfo

A vulnerability was found in Erlang OTP (version now known) and classified as problematic. This issue affects the function httpd_request:validate_uri of the component httpd. The manipulation with an unknown input leads to a path traversal vulnerability. Using CWE to declare the problem leads to CWE-22. The product uses external input to construct a pathname that is intended to identify a file or directory that is located underneath a restricted parent directory, but the product does not properly neutralize special elements within the pathname that can cause the pathname to resolve to a location that is outside of the restricted directory. Impacted is confidentiality. The summary by CVE is:

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. Whether OTP before OTP 17.0, corresponding to inets before 5.10, is affected is unknown.

The advisory is shared at github.com. The identification of this vulnerability is CVE-2026-66835 since 08/17/2026. The exploitation is known to be easy. The attack may be initiated remotely. No form of authentication is needed for a successful exploitation. Technical details are known, but no exploit is available. The price for an exploit might be around USD $0-$5k at the moment (estimation calculated on 09/03/2026). MITRE ATT&CK project uses the attack technique T1006 for this issue.

The vulnerability scanner Nessus provides a plugin with the ID 342478 (Linux Distros Unpatched Vulnerability : CVE-2026-66835), which helps to determine the existence of the flaw in a target environment.

There is no information about possible countermeasures known. It may be suggested to replace the affected object with an alternative product.

The vulnerability is also documented in the databases at Tenable (342478), EUVD (EUVD-2026-69245) and CERT Bund (WID-SEC-2026-3146). Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

Affected

• Open Source Erlang/OTP

Productinfo

Vendor

• Erlang

Name

• OTP

Website

• Product: https://github.com/erlang/otp/

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Entryinfo

Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

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