CVE-2026-114216 in bandit
Summary
by MITRE • 10/26/2026
Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling') vulnerability in the HTTP/1.1 chunked body reader of mtrudel bandit allows an unauthenticated remote attacker to smuggle a second request past a front-end proxy via a chunk extension that contains a bare LF.
The chunked reader in lib/bandit/http1/socket.ex takes the chunk-size line to be everything up to the first CRLF and discards everything after ; without checking it against the RFC 9112 chunk-ext grammar, so bare LF, bare CR and other control bytes pass. A proxy that ends the size line at a bare LF reads 2;\nxx\r\n40\r\n... as one request whose second chunk holds a GET /admin, while Bandit ends the body early and dispatches GET /admin as a separate pipelined request. Deployments without such a proxy in front of Bandit are not affected.
This issue affects bandit: from 1.12.4 before 1.14.0.
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Analysis
by VulDB Data Team • 10/26/2026
The vulnerability identified involves an inconsistent interpretation of HTTP requests, specifically manifesting as HTTP Request Smuggling within the HTTP/1.1 chunked body reader implementation in the mtrudel bandit web server library. This flaw allows an unauthenticated remote attacker to smuggle a second request past a front-end proxy by exploiting how the parser handles chunk extensions that contain bare line feed characters. The core technical deficiency lies in the lib/bandit/http1/socket.ex module, which processes the chunk-size line by capturing everything up to the first carriage return and line feed sequence while discarding any subsequent content following a semicolon without validating it against the strict grammar defined in RFC 9112 for chunk extensions. Consequently, control bytes such as bare line feeds or bare carriage returns are erroneously accepted as valid parts of the chunk size specification rather than being rejected as malformed input.
The operational impact arises from the divergent parsing behaviors between bandit and standard HTTP proxies when encountering these malformed chunks. In a typical deployment scenario where a front-end proxy sits in front of bandit, an attacker can craft a request with a chunk header like 2; followed by a bare line feed and then additional data such as xx\r\n40\r\n... The proxy, adhering to stricter or different parsing logic that may terminate the size line at the first occurrence of any whitespace including a bare line feed, interprets this sequence as a single request where the second chunk contains specific payload data. In contrast, bandit terminates its body processing early due to its lenient acceptance of the control byte, thereby dispatching the subsequent content as a separate pipelined request. This discrepancy creates an ambiguity that enables request smuggling attacks, potentially allowing attackers to bypass access controls or inject malicious requests into backend systems by manipulating how the front-end proxy and the origin server interpret the boundaries of HTTP messages.
This vulnerability is classified under CWE-440, which denotes unintended behavior in a product when it receives input containing control characters not expected as valid data, and aligns with MITRE ATT&CK technique T1537, specifically related to communication through application layer protocols where inconsistent parsing leads to security bypasses. The issue affects versions of bandit from 1.12.4 up to but excluding version 1.14.0. Deployments that do not utilize a front-end proxy in front of the bandit server are generally not susceptible to this specific smuggling vector, as there is no intermediate entity with differing parsing logic to create the ambiguity required for exploitation. Mitigation strategies involve upgrading to a patched version of bandit where the chunked body reader strictly enforces RFC 9112 compliance by rejecting any control characters within chunk extensions or ensuring that input validation layers are robust enough to filter out such malformed sequences before they reach the application server logic.