Log in Start free

Vulnerability · Published Sep 1, 2026 · Assigned by EEF

CVE-2026-66835httpd mod_auth directory protection bypassed by a doubled slash in the request path

High 8.2

In plain English

A high-severity security flaw in OTP from Erlang. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 1.0% (higher than 62% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 4.0)8.2High
Exploit odds (30 days)1.0%top 37.8% of all CVEs
Exploited in the wildNo reportsCISA SSVC: none
Attack toolingNoneno public tooling known

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.

Affected packages & fixed versions

EcosystemPackageFixed inAdvisory
Debian:12erlangno fix listedDEBIAN-CVE-2026-66835
Debian:13erlang1:27.3.4.1+dfsg-1+deb13u4DEBIAN-CVE-2026-66835
Debian:14erlang1:29.0.6+dfsg-1DEBIAN-CVE-2026-66835
Ubuntu:22.04:LTSerlang1:24.2.1+dfsg-1ubuntu0.7UBUNTU-CVE-2026-66835
Ubuntu:22.04:LTSerlang1:24.2.1+dfsg-1ubuntu0.7USN-8827-1
Ubuntu:24.04:LTSerlang1:25.3.2.8+dfsg-1ubuntu4.7USN-8827-1
Ubuntu:24.04:LTSerlang1:25.3.2.8+dfsg-1ubuntu4.7UBUNTU-CVE-2026-66835
Ubuntu:26.04:LTSerlang1:27.3.4.6+dfsg-1ubuntu0.1USN-8827-1
Ubuntu:26.04:LTSerlang1:27.3.4.6+dfsg-1ubuntu0.1UBUNTU-CVE-2026-66835

Affected products (as reported)

VendorProductVersions
Erlang OTP 17.0 – before 27.3.4.1728.0 – before 28.5.0.629.0 – before 29.0.6
Erlang OTP 5.10 – before 9.3.2.79.4 – before 9.6.2.39.7 – before 9.7.2
Erlang OTP 84adefa331c4159d432d22840663c38f155cd4c1 – before *

Weakness: CWE-50 · Vector: CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N

References