# 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.

- **Severity:** High 8.2 (`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`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 1 Sep 2026
- **Updated:** 8 Sep 2026
- **Also known as:** AZL-98463, DEBIAN-CVE-2026-66835, EEF-CVE-2026-66835, GHSA-r4vv-vc2c-2fw6, UBUNTU-CVE-2026-66835

## 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 (Path Equivalence: '//multiple/leading/slash')

## Which versions are affected by CVE-2026-66835?


## How do I fix CVE-2026-66835?

Upgrade to a fixed version.

## Is CVE-2026-66835 being exploited?

There is no known exploitation of CVE-2026-66835 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-66835 and fix it if it is affected.

What it is: 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.
Exploitation: There is no known exploitation of CVE-2026-66835 in the wild and no public exploit code.

Affected product: Erlang OTP. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-66835/ (Markdown: https://insights.sbomify.com/CVE-2026-66835/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-66835
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-66835
- OSV: https://osv.dev/vulnerability/CVE-2026-66835

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-66835/
Summaries are generated and may contain mistakes; the official description above is the record.