Bug 2464592 (CVE-2026-39807)

Summary: CVE-2026-39807 bandit: Bandit: Transport-state spoofing leads to information disclosure and security bypass
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
Status: NEW --- QA Contact:
Severity: medium Docs Contact:
Priority: medium    
Version: unspecifiedCC: jwong, omaciel, teagle, ttakamiy
Target Milestone: ---Keywords: Security
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Hardware: All   
OS: Linux   
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A flaw was found in bandit. An unauthenticated client can exploit this vulnerability by spoofing the transport state on plaintext HTTP connections. By declaring an HTTPS scheme over a non-secure TCP connection, the system incorrectly registers the connection as secure. This can lead to sensitive cookies being sent over plaintext, bypassing security redirects, and potentially affecting Cross-Site Request Forgery (CSRF) and SameSite protections, resulting in information disclosure and security bypass.
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oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
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Bug Depends On: 2467994    
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Description OSIDB Bzimport 2026-05-01 21:01:58 UTC 
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.