Weakness (CWE)
CWE-444: Inconsistent Interpretation of HTTP Requests
The product acts as an intermediary HTTP agent
(such as a proxy or firewall) in the data flow between two
entities such as a client and server, but it does not
interpret malformed HTTP requests or responses in ways that
are consistent with how the messages will be processed by
those entities that are at the ultimate destination.
More detail
HTTP requests or responses ("messages") can be
malformed or unexpected in ways that cause web servers or
clients to interpret the messages in different ways than
intermediary HTTP agents such as load balancers, reverse
proxies, web caching proxies, application firewalls,
etc. For example, an adversary may be able to add duplicate
or different header fields that a client or server might
interpret as one set of messages, whereas the intermediary
might interpret the same sequence of bytes as a different
set of messages. For example, discrepancies can arise in
how to handle duplicate headers like two Transfer-encoding
(TE) or two Content-length (CL), or the malicious HTTP
message will have different headers for TE and
CL.
The inconsistent parsing and interpretation of messages
can allow the adversary to "smuggle" a message to the
client/server without the intermediary being aware of it.
This weakness is usually the result of the usage
of outdated or incompatible HTTP protocol versions in the
HTTP agents.
How to prevent it (4 mitigations)
-
Implementation
Use a web server that employs a strict HTTP parsing procedure, such as Apache [REF-433].
-
Implementation
Use only SSL communication.
-
Implementation
Terminate the client session after each request.
-
System Configuration
Turn all pages to non-cacheable.
Source: MITRE CWE-444
406 results · Feed
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Medium 4.8
In JetBrains Ktor before 3.6.1 hTTP request smuggling was possible in the CIO engine
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Low 2.9
Caddy: RFC 7230 §6.1 compliance issue / Hop-by-hop headers that leak through
Caddy is an extensible server platform that uses TLS by default. Prior to 2.11.5, the reverse proxy's finalizeResponse method in modules/caddyhttp/reverseproxy/reverseproxy.go handles an upstream 101 Switching Protocols response before running removeConnectio…
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High 7.5
Apache Sling Engine: Hand-rolled parameter parser diverges from RFC/container parsing, enabling smuggling
Inconsistent interpretation of HTTP requests ('HTTP Request/Response smuggling') vulnerability in Apache Sling Engine. The engine's query/form parser accepts non-standard percent-escapes, wrong charsets, and continues request processing on such errors. This i…
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Low 3.7
Wasmtime before 36.0.19, 37.0.0 before 48.0.7, and 49.0.0 before 49.0.4 wasi-http Request Smuggling
Wasmtime before 36.0.19, 37.0.0 before 48.0.7, and 49.0.0 before 49.0.4 contains a request smuggling vulnerability in wasi-http that allows guests to set multiple conflicting content-length headers. Malicious guests can make the host send HTTP requests with c…
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Medium 5.3
Wasmtime 46.0.0 before 48.0.7 and 49.0.0 before 49.0.4 HTTP Response Splitting via wasi-http
Wasmtime 46.0.0 before 48.0.7 and 49.0.0 before 49.0.4 contains a response splitting vulnerability in wasi-http p3 that allows guests to set unvalidated content-length headers. Malicious wasip3 guests can splice an existing body into a new response with an in…
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Medium 6.9
uhttpd vulnerable to HTTP request smuggling via case-sensitive Transfer-Encoding matching
uhttpd is a small HTTP server. In unpatched repository snapshots, `client_parse_header()` in `client.c` lowercases header names but compares the `Transfer-Encoding` value to `chunked` using case-sensitive `strcmp`. A mixed-case transfer-coding token is accept…
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Low 3.7
uhttpd vulnerable to HTTP request smuggling via invalid chunk-length state reset
uhttpd is a small HTTP server. In unpatched repository snapshots, `client_poll_post_data()` in `client.c` consumes an invalid chunk-length line, such as a size exceeding INT_MAX, then clears `r->content_length` and `r->transfer_chunked` without draining the r…
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Medium 6.9
uhttpd: HTTP request smuggling via ubus POST body parse-error desync
uhttpd is a small HTTP server. In unpatched repository snapshots, `uh_ubus_data_send()` in `ubus.c` can desynchronize HTTP request boundaries when a `POST /ubus` JSON body arrives in multiple TCP segments. An initial segment completing a JSON object sets `du-…
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Critical 9.1
Starlet versions before 0.33 for Perl send a body in responses to HEAD requests, corrupting the next response on a persistent or pipelined connection
Starlet versions before 0.33 for Perl send a body in responses to HEAD requests, corrupting the next response on a persistent or pipelined connection. The request method is not passed to the response writer, so whatever body the application returns for a HEAD…
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Medium 6.5
Undertow: undertow: chunkreader message length permits chunk-size overflow
A flaw was found in the ChunkReader component of the Undertow web server, which is used to handle chunked transfer encoding in HTTP requests. The issue occurs because a security check for the chunk size is performed before the value is shifted, allowing a spe…
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Critical 9.1
Echo: Rejected WebSocket upgrades can bypass Echo route-level access controls
Echo is a Go web framework. From 4.0.0 until 4.16.1 and 5.4.1, Echo's Proxy middleware selects a raw tunnel from a client WebSocket upgrade request before verifying that the configured upstream accepted the upgrade. If the upstream rejects the upgrade with an…
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Low 2.0
Lenient parsing of integers for response body and chunk framing
Response body and chunk parsing would handle non-hex or negative integers incorrectly which could result in misinterpreting HTTP response contents.
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Medium 6.3
Chunk extensions accept bare LF and CR, enabling request smuggling in Bandit
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 exten…
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Critical 9.1
Starman versions before 0.4019 for Perl send response bodies for HEAD requests, desynchronizing responses on keep-alive connections
Starman versions before 0.4019 for Perl send response bodies for HEAD requests, desynchronizing responses on keep-alive connections. For a HEAD request Starman omits chunked framing but still writes the body returned by the application, on both the array and …
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Medium 5.4
Twisted: HTTP Request Smuggling in twisted.web via a Bare CR or LF in a Header Value
Twisted is an event-based framework for internet applications, supporting Python 3.6+. Prior to 26.10.0rc1, twisted.web.http.HTTPChannel.headerReceived rejects a NUL byte in an HTTP header value but accepts a bare carriage return or bare line feed. Because Tw…
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High 7.5
Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling') in GitLab
GitLab has remediated an issue in GitLab CE/EE affecting all versions from 18.3 before 19.3.6, 19.4 before 19.4.3, and 19.5 before 19.5.1 that, under certain conditions, an unauthenticated user could have poisoned a shared cache's OAuth/OIDC discovery documen…
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Critical 9.3
Apache Traffic Server: HEAD requests carrying Content-Length or Transfer-Encoding enable request smuggling
Apache Traffic Server allows request smuggling via HEAD requests that carry Content-Length or Transfer-Encoding. This issue affects Apache Traffic Server: from 8.0.0 through 8.1.11, from 9.0.0 through 9.2.15, from 10.0.0 through 10.1.4, 10.2.0. Users are reco…
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Critical 9.3
Apache Traffic Server: A malformed 302 response bypasses parse-error rejection through the Transfer-Encoding: chunked carve-out
Apache Traffic Server forwarded a malformed 302 response that should have been rejected as a parse error, because the Transfer-Encoding: chunked carve-out bypassed the rejection path. A response that two peers can read differently is then stored and served, a…
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High 8.7
Apache Traffic Server: An unread Expect: 100-continue request body is framed as a new request
When a client sends a POST with Expect: 100-continue and the origin answers before reading the body, Apache Traffic Server parses the unread body left on the client connection as the next request. An attacker behind a front-end proxy that shares connections t…
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High 8.9
Apache Traffic Server: Origin connection still owed a request body is reused, enabling request smuggling
Apache Traffic Server can return an origin connection to the shared pool while the origin is still waiting on a request body the client declared but never fully sent, including when the client used Expect: 100-continue. The origin then reads a later request o…
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High 7.5
Apache bRPC: HTTP Request Smuggling and Header Injection via Lenient HTTP/1.1 Header Parsing
Inconsistent interpretation of HTTP requests (HTTP request/response smuggling) in the bundled HTTP/1.1 parser of Apache bRPC (version < 1.18.0) on all platforms allows remote attackers to smuggle requests and inject headers when bRPC is deployed behind a prox…
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Medium 6.9
NetX Duo Web HTTP server interprets request body content as HTTP header fields
The Web add-on's HTTP server searches the entire request packet for header fields instead of stopping at the end of the header section. A header field name placed in the request body is therefore reported to the server as though it were a header, which lets a…
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High 8.7
Pingora forwards client-nominated Connection headers to HTTP/1 upstreams, allowing ACL bypass in specific chained deployments
Summary Before version 0.9.0, the HTTP/1 upstream path in pingora-proxy passed the downstream request through upstream_request_filter and wrote it to the upstream without removing the client's Connection header, other hop-by-hop headers, or the headers Connec…
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Medium 6.3
Pingora HTTP/2 :authority and Host header mismatch enables cache poisoning and host-based access control bypass
Summary Before version 0.9.0, Pingora accepted HTTP/2 requests whose Host header differed from the :authority pseudo-header. Request filters, cache keys, and logs that read the request URI (session.req_header().uri) saw the :authority value, but the upstream …
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Medium 6.3
AIOHTTP: Pure-Python parser request smuggling
AIOHTTP is an asynchronous HTTP client/server framework for asyncio and Python. Prior to 3.14.4, the pure Python parser accepts ambiguous HTTP request framing. An unauthenticated attacker can consequently smuggle requests when an application uses AIOHTTP_NO_E…
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High 7.1
pupnp: Integer truncation in HTTP Content-Length parsing enables request smuggling
pupnp is an SDK for development of UPnP device and control point applications. Prior to 2.0.2, raw_to_int in upnp/src/genlib/net/http/httpparser.c parses Content-Length with strtol and casts the resulting long to a 32-bit int before the caller stores it as un…
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High 8.7
In Eclipse Vert.x versions [5.0.0,5.0.12] or [5.1.0,5.1.9] or [5.2.0, 5.2.0], the Vert.x HTTP/1.x decoder uses a canoni…
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High 7.2
Busybox: busybox: http request smuggling via pipelined requests in httpd reverse proxy
A flaw was found in BusyBox httpd's reverse proxy feature. When the proxy is configured to forward requests matching a URL prefix to a backend server, only the first HTTP request on a TCP connection has its path rewritten. An attacker can send a pipelined sec…
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Critical 9.4
ASP.NET Core Tampering Vulnerability
Inconsistent interpretation of http requests ('http request/response smuggling') in ASP.NET Core allows an unauthorized attacker to perform tampering over a network.
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Critical 9.1
ASP.NET Core Security Feature Bypass Vulnerability
Inconsistent interpretation of http requests ('http request/response smuggling') in ASP.NET Core allows an unauthorized attacker to bypass a security feature over a network.
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High 7.7
Squid Request Smuggling in HTTP Transfer-Encoding
Squid is a caching proxy for the Web. From 3.3.0.1 to before 7.6, due to an improper enforcement of behavioral workflow bug, Squid is vulnerable to a Request Smuggling attack against HTTP/1.1 Transfer-Encoding. HTTP header parsing (`src/HttpHeader.cc`) accept…
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High 7.5
HTTP/1 server connection desynchronization after 2xx CONNECT response in net/http
When an HTTP server handler sends a 2xx response to an HTTP/1 CONNECT request and returns without hijacking the connection, the server improperly continues to read and serve requests from the connection. Since a 2xx response to an HTTP/1 CONNECT converts the …
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High 7.5
HTTP/2 transport accepts malformed framing-related headers in net/http
Historically, we have been rather lax about malformed framing-related headers in our HTTP/2 implementation, as they cannot interfere with HTTP/2 framing. However, this makes it possible for our HTTP/2 implementation to forward responses containing such header…
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High 7.5
HTTP/1 client connection desynchronization after CONNECT rejection in net/http
When http.Transport sends an HTTP/1 CONNECT request with a non-empty Request.Body, it writes the body directly to the connection without framing after the request headers. If the server rejects the CONNECT request with a non-2xx keep-alive response, Transport…
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Low 3.6
Front-end Desynchronization Vulnerability in Progress® Telerik® Fiddler® Classic
In Progress® Telerik® Fiddler® Classic for Windows, versions prior to v6.0.20262.10021, front-end request desynchronization is possible in the proxy request forwarding component. A request that contains both a Content-Length and a Transfer-Encoding header is …
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Medium 6.3
HTTP Request Smuggling Vulnerability in Progress® Telerik® Fiddler® Classic
In Progress® Telerik® Fiddler® Classic for Windows, versions prior to v6.0.20262.10021, HTTP request smuggling is possible in the proxy request forwarding component. Requests containing multiple Content-Length headers with conflicting values are forwarded ver…
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High 7.5
Apache HTTP Server: mod_proxy_uwsgi Transfer-Encoding response smuggling
Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling') response smuggling vulnerability in Apache HTTP Server via mod_proxy_uwsgi and a crafted uwsgi response with Transfer-Encoding. This issue affects Apache HTTP Server: from 2.4.30…
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Medium 5.3
Libsoup: soupserver: http/1 request smuggling via undrained expect: 100-continue body
A flaw was found in SoupServer (libsoup). When an HTTP/1.x client sends a request with Expect: 100-continue and a request body, and SoupServer returns an early final (non-1xx) response before the body is read, the server neither drains the declared body bytes…
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Medium 6.3
Mint HTTP/1 client applies chunked framing when chunked is not the final transfer coding, enabling response smuggling through intermediaries
Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling') vulnerability in elixir-mint mint allows a malicious HTTP/1 server to desynchronize an intermediary and the Mint client on a pooled connection, poisoning the responses to subsequ…
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Critical 9.3CVE-2026-88773 Public exploit
HTTP Request Smuggling
Inconsistent interpretation of HTTP requests ('HTTP Request/Response smuggling') vulnerability in Citrix NetScaler ADC and Citrix NetScaler Gateway. This issue affects ADC: before 14.1-73.37, before 13.1-64.23, before 14.1-73.37 FIPS, and before 13.1-37.279 a…