CVE ID :CVE-2026-39807

Published : May 1, 2026, 9:16 p.m. | 1 hour, 3 minutes ago

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.

Severity: 6.3 | MEDIUM

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