HTTP request smuggling via duplicate Content-Length headers
Published May 1, 2026 · Updated May 1, 2026
HTTP request smuggling in Mat Trudel Bandit before 1.11.0 allows remote attackers to bypass proxy controls via duplicate Content-Length headers. Bandit.Headers.get_content_length/1 uses List.keyfind/3 to select only the first matching header, ignoring a conflicting duplicate and treating leftover body bytes as a pipelined request. Exploitation requires an HTTP/1.1 keep-alive path through a permissive front-end that uses the last length; the smuggled request can bypass edge WAF rules, path ACLs, rate limits, and audit logging.
Summary
What happened
HTTP request smuggling in Mat Trudel Bandit before 1.11.0 allows remote attackers to bypass proxy controls via duplicate Content-Length headers. Bandit.Headers.get_content_length/1 uses List.keyfind/3 to select only the first matching header, ignoring a conflicting duplicate and treating leftover body bytes as a pipelined request. Exploitation requires an HTTP/1.1 keep-alive path through a permissive front-end that uses the last length; the smuggled request can bypass edge WAF rules, path ACLs, rate limits, and audit logging.
The record
- CVE
- CVE-2026-39805
- Published
- May 1, 2026
- Updated
- May 1, 2026
- Vendor
- Mat Trudel
- Product
- Bandit
- Classifications
- CWE-444, CAPEC-33, T1190
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- May 1, 2026CVE publishedPublication date reported by the CVE source.
- May 1, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
Compare these published version ranges with your installed build and any vendor patches.
- Affected versionversion=0 <1.11.0
What conditions does exploitation require?
What is affected?
Published CVSS scores
CVSS describes severity. EPSS estimates exploitation probability.
Attacks
What attackers are doing with it
Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.
Weakness, pattern, technique
Public exploit references
- Bandit duplicate Content-Length demonstration scriptproof of concept · demonstrated
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Technologies
Your stack
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Your stack
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