# CVE-2026-39807: Client-supplied URI scheme trusted without transport verification in bandit

> Attackers can spoof HTTPS scheme on plaintext connections, bypassing SSL redirects and secure cookie protections in Bandit web server.

- **Severity:** Medium 6.3 (`CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:L/VI:L/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 May 2026
- **Updated:** 27 May 2026
- **Also known as:** EEF-CVE-2026-39807, GHSA-375f-4r2h-f99j

## What is CVE-2026-39807?

CVE-2026-39807 is a medium-severity vulnerability in mtrudel bandit, published on 1 May 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

Reliance on Untrusted Inputs in a Security Decision vulnerability in mtrudel bandit allows unauthenticated transport-state spoofing on plaintext HTTP connections.

'Elixir.Bandit.Pipeline':determine_scheme/2 in lib/bandit/pipeline.ex returns the client-supplied URI scheme verbatim, ignoring the transport's secure? flag. HTTP/1.1 absolute-form request targets (e.g. GET https://victim/path HTTP/1.1) and the HTTP/2 :scheme pseudo-header are both attacker-controlled strings that flow through this function. Over a plaintext TCP connection, a client can declare https and Bandit will set conn.scheme = :https even though no TLS was negotiated.

Downstream Plug consumers that branch on conn.scheme are silently misled: Plug.SSL's already-secure branch skips its HTTP→HTTPS redirect, cookies emitted with secure: true are sent over plaintext, audit logs record requests as having arrived over HTTPS, and CSRF/SameSite gating may make incorrect decisions.

This issue affects bandit: from 1.0.0 before 1.11.0.

Weakness: CWE-807 (Reliance on Untrusted Inputs in a Security Decision)

## Which versions are affected by CVE-2026-39807?

3 open source packages ship an affected version, including bandit.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `bandit` | Hex | From 1.0.0 | 1.11.0 |
| `bandit` | Hex | From 1.0.0 | 1.11.0 |
| `bandit` | Hex | From 1.0.0 | 1.11.0 |

## How do I fix CVE-2026-39807?

Upgrade bandit to 1.11.0 or later.

## Is CVE-2026-39807 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-39807 exists.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-39807 and fix it if it is affected.

What it is: CVE-2026-39807 is a medium-severity vulnerability in mtrudel bandit, published on 1 May 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-2026-39807 exists.

Affected packages and fixed versions:
- bandit (Hex): affected from 1.0.0; fixed in 1.11.0
- bandit (Hex): affected from 1.0.0; fixed in 1.11.0
- bandit (Hex): affected from 1.0.0; fixed in 1.11.0

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-2026-39807/ (Markdown: https://insights.sbomify.com/CVE-2026-39807/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-39807
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-39807
- OSV: https://osv.dev/vulnerability/CVE-2026-39807

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-39807/
Summaries are generated and may contain mistakes; the official description above is the record.