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

Quick assessment

Affected
mtrudel bandit
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

Bandit是Mat Trudel个人开发者的一款高性能HTTP与WebSocket服务器。 Bandit 1.0.0版本至1.11.0之前版本存在安全漏洞，该漏洞源于依赖不可信输入进行安全决策，可能导致未经身份验证的攻击者在明文HTTP连接上伪造传输状态。

AI Predicted 7.5 Difficulty: Easy EPSS 0.52% · P42

Possible ATT&CK Techniques 1 AI

T1190 · Exploit Public-Facing Application

Affected Version Matrix 2

VendorProduct Version RangeStatus
mtrudel bandit 1.0.0< 1.11.0 affected
ff2f829326cd5dcf7335939aef9775269d881e28< 45feea20dea8af7ffd7245271107b695c040e667 affected
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I. Basic Information for CVE-2026-39807

Vulnerability Information
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Vulnerability Title
Client-supplied URI scheme trusted without transport verification in bandit
Source: CVE Program / CVE List V5
Vulnerability 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.
Source: CVE Program / CVE List V5
CVSS Information
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
Source: CVE Program / CVE List V5
Vulnerability Type
在安全决策中依赖未经信任的输入
Source: CVE Program / CVE List V5
Vulnerability Title
Bandit 安全漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
Bandit是Mat Trudel个人开发者的一款高性能HTTP与WebSocket服务器。 Bandit 1.0.0版本至1.11.0之前版本存在安全漏洞，该漏洞源于依赖不可信输入进行安全决策，可能导致未经身份验证的攻击者在明文HTTP连接上伪造传输状态。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
mtrudel bandit 1.0.0 ~ 1.11.0 cpe:2.3:a:mtrudel:bandit:*:*:*:*:*:*:*:*
mtrudel bandit ff2f829326cd5dcf7335939aef9775269d881e28 ~ 45feea20dea8af7ffd7245271107b695c040e667 cpe:2.3:a:mtrudel:bandit:*:*:*:*:*:*:*:*

II. Public POCs for CVE-2026-39807

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III. Intelligence Information for CVE-2026-39807

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Patches & Fixes for CVE-2026-39807 (1)

Vendor Advisories for CVE-2026-39807 (2)

Other References for CVE-2026-39807 (1)

Same Patch Batch · mtrudel · 2026-05-01 · 5 CVEs total

CVE-2026-39805 6.3 MEDIUM CL.CL HTTP request smuggling via duplicate Content-Length in bandit
CVE-2026-42788 HTTP/2 frame size limit checked after body is buffered in bandit
CVE-2026-42786 WebSocket fragmented message reassembly unbounded in bandit
CVE-2026-39804 WebSocket permessage-deflate inflate has no output-size cap in bandit

IV. Related Vulnerabilities

Same product: bandit
Same vendor: mtrudel
Same weakness: CWE-807

V. Comments for CVE-2026-39807

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