# CVE-2026-91143: goproxy through 15.3 Authentication Bypass via CONNECT

> Unauthenticated attackers can bypass proxy authentication via CONNECT requests to relay arbitrary TCP traffic and access restricted destinations.

- **Severity:** Medium 6.9 (`CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:N/SC:L/SI:L/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 14 Sep 2026
- **Updated:** 24 Sep 2026
- **Also known as:** GHSA-pvfx-f5gx-wj35

## What is CVE-2026-91143?

CVE-2026-91143 is a medium-severity authentication bypass vulnerability in snail007 goproxy, published on 14 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

goproxy through 15.3 fails to apply HTTP proxy basic authentication to CONNECT tunnel requests, allowing unauthenticated clients to bypass credential requirements. Attackers can issue CONNECT requests to establish tunnels through the authenticated proxy without providing credentials, enabling arbitrary TCP traffic relay and access to restricted destinations.

Weakness: CWE-288 (Authentication Bypass Using an Alternate Path or Channel)

## Which versions are affected by CVE-2026-91143?


## How do I fix CVE-2026-91143?

No fix has been published for CVE-2026-91143 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-91143 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-91143 exists.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-91143 and fix it if it is affected.

What it is: CVE-2026-91143 is a medium-severity authentication bypass vulnerability in snail007 goproxy, published on 14 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-91143 exists.

Affected product: snail007 goproxy. 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-2026-91143/ (Markdown: https://insights.sbomify.com/CVE-2026-91143/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-91143
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-91143
- OSV: https://osv.dev/vulnerability/CVE-2026-91143

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-91143/
Summaries are generated and may contain mistakes; the official description above is the record.