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CVE-2026-39805— CL.CL HTTP request smuggling via duplicate Content-Length 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 1.11.0之前版本存在环境问题漏洞，该漏洞源于对重复Content-Length标头的处理不一致，可能导致HTTP请求夹带攻击。

CVSS 6.3 · Medium EPSS 0.55% · P44

Possible ATT&CK Techniques 1 AI

T1102 · Web Service

Affected Version Matrix 2

VendorProduct Version RangeStatus
mtrudel bandit 0.1.0< 1.11.0 affected
7bc8d97cd22697c299baa8012b7f419a7606a80c< f2ca636eb6df385219957e8934e9fc6efa1630d1 affected
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I. Basic Information for CVE-2026-39805

Vulnerability Information
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Vulnerability Title
CL.CL HTTP request smuggling via duplicate Content-Length in bandit
Source: CVE Program / CVE List V5
Vulnerability Description
Inconsistent Interpretation of HTTP Requests vulnerability in mtrudel bandit allows HTTP request smuggling via duplicate Content-Length headers. 'Elixir.Bandit.Headers':get_content_length/1 in lib/bandit/headers.ex uses List.keyfind/3, which returns only the first matching header. When a request contains two Content-Length headers with different values, Bandit silently accepts it, uses the first value to read the body, and dispatches the remaining bytes as a second pipelined request on the same keep-alive connection. RFC 9112 §6.3 requires recipients to treat this as an unrecoverable framing error. When Bandit sits behind a proxy that picks the last Content-Length value and forwards the request rather than rejecting it, an unauthenticated attacker can smuggle requests past edge WAF rules, path-based ACLs, rate limiting, and audit logging. This issue affects bandit: 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
HTTP请求的解释不一致性(HTTP请求私运)
Source: CVE Program / CVE List V5
Vulnerability Title
Bandit 环境问题漏洞
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 1.11.0之前版本存在环境问题漏洞，该漏洞源于对重复Content-Length标头的处理不一致，可能导致HTTP请求夹带攻击。
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 0.1.0 ~ 1.11.0 cpe:2.3:a:mtrudel:bandit:*:*:*:*:*:*:*:*
mtrudel bandit 7bc8d97cd22697c299baa8012b7f419a7606a80c ~ f2ca636eb6df385219957e8934e9fc6efa1630d1 cpe:2.3:a:mtrudel:bandit:*:*:*:*:*:*:*:*

II. Public POCs for CVE-2026-39805

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III. Intelligence Information for CVE-2026-39805

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Patches & Fixes for CVE-2026-39805 (1)

Vendor Advisories for CVE-2026-39805 (3)

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

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-2026-39807 Client-supplied URI scheme trusted without transport verification 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-444

V. Comments for CVE-2026-39805

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