CVE-2026-66835
Fix: erlang/otp@bac19ebCVE-2026-66835 is a CWE-50 vulnerability. O3 Security confirms whether CVE-2026-66835 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
httpd mod_auth directory protection bypassed by a doubled slash in the request path
Description
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. Whether OTP before OTP 17.0, corresponding to inets before 5.10, is affected is unknown.
Configuration
Only servers that protect a directory with mod_auth, by configuring a directory block with authentication requirements, are affected. A server that serves no authenticated directory has no protection for this issue to bypass.
Detection & mitigation playbook
VulnerabilityDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for the affected component. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Remediation status
No patched version of the affected component has shipped for CVE-2026-66835 yet. Where your build allows, override or pin the dependency away from the vulnerable range, and apply any maintainer-recommended mitigation.
Mitigate without a patch
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 pinpoints whether CVE-2026-66835 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to CVE-2026-66835. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2026-66835 in your dependencies?
O3 detects CVE-2026-66835 across dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.