CVE-2026-66835 httpd mod_auth directory protection bypassed by a doubled slash in the request path
Remote attackers can bypass authentication and read protected files in Erlang OTP httpd by using a doubled slash in the request path.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-66835?
CVE-2026-66835 is a high-severity path traversal vulnerability in Erlang OTP, published on 1 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
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.
Weakness: CWE-50
Which versions are affected by CVE-2026-66835?
How do I fix CVE-2026-66835?
Upgrade to a fixed version.
Upgrade, and resolve every user-supplied path against an allowed base folder before opening it. More about Path traversal.
Is CVE-2026-66835 being exploited?
There is no known exploitation of CVE-2026-66835 in the wild and no public exploit code.
Sources
Also known as AZL-98463, DEBIAN-CVE-2026-66835, EEF-CVE-2026-66835, GHSA-r4vv-vc2c-2fw6, UBUNTU-CVE-2026-66835.