CVE-2026-39807
Severity CVSS v4.0:
MEDIUM
Type:
Unavailable / Other
Publication date:
01/05/2026
Last modified:
02/05/2026
Description
Reliance on Untrusted Inputs in a Security Decision vulnerability in mtrudel bandit allows unauthenticated transport-state spoofing on plaintext HTTP connections.<br />
<br />
&#39;Elixir.Bandit.Pipeline&#39;:determine_scheme/2 in lib/bandit/pipeline.ex returns the client-supplied URI scheme verbatim, ignoring the transport&#39;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.<br />
<br />
Downstream Plug consumers that branch on conn.scheme are silently misled: Plug.SSL&#39;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.<br />
<br />
This issue affects bandit: from 1.0.0 before 1.11.0.
Impact
Base Score 4.0
6.30
Severity 4.0
MEDIUM
References to Advisories, Solutions, and Tools
- https://cna.erlef.org/cves/CVE-2026-39807.html
- https://github.com/mtrudel/bandit/commit/45feea20dea8af7ffd7245271107b695c040e667
- https://github.com/mtrudel/bandit/security/advisories/GHSA-375f-4r2h-f99j
- https://osv.dev/vulnerability/EEF-CVE-2026-39807
- https://github.com/mtrudel/bandit/security/advisories/GHSA-375f-4r2h-f99j