Bug 2464590 (CVE-2026-39805)

Summary: CVE-2026-39805 bandit: Bandit: HTTP Request Smuggling via Duplicate Content-Length Headers
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
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Priority: high    
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 HTTP server. This vulnerability allows for HTTP request smuggling due to the server's inconsistent handling of duplicate Content-Length headers in HTTP requests. An unauthenticated attacker can exploit this by sending a specially crafted request. If Bandit is operating behind a proxy that interprets these headers differently, the attacker can bypass security mechanisms like Web Application Firewalls (WAFs), access controls, and rate limiting, potentially leading to unauthorized actions or access.
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Bug Depends On: 2477948    
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Description OSIDB Bzimport 2026-05-01 21:01:49 UTC 
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 ยง6.3 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.