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CVE PROGRAM SOURCE RECORD6.3 Medium

CVE-2026-39807

Client-supplied URI scheme trusted without transport verification in bandit

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.

Affected products

Version statuses are supplied by the assigning organization. Consult the original record for detailed ranges and platform conditions.

mtrudel bandit

Default version status: unaffected

  • 1.0.0 to < 1.11.0affected
pkg:hex/bandit

mtrudel bandit

Default version status: unaffected

  • ff2f829326cd5dcf7335939aef9775269d881e28 to < 45feea20dea8af7ffd7245271107b695c040e667affected
pkg:github/mtrudel/bandit

References