Denial of Service (DoS) Affecting http-proxy package, versions <1.18.1



    Attack Complexity Low
    User Interaction Required
    Availability High

    Threat Intelligence

    Exploit Maturity Proof of concept

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  • Snyk ID SNYK-JS-HTTPPROXY-569139
  • published 16 May 2020
  • disclosed 14 May 2020
  • credit Grant Murphy

Introduced: 14 May 2020

CVE NOT AVAILABLE CWE-400 Open this link in a new tab

How to fix?

Upgrade http-proxy to version 1.18.1 or higher.


http-proxy is a library that HTTP proxying for the masses.

Affected versions of this package are vulnerable to Denial of Service (DoS). HTTP requests with long bodies can crash the proxy sever via triggering an ERR_HTTP_HEADERS_SENT unhandled exception.

Note This vulnerability is only viable if proxy server uses the proxyReq.setHeader function to set headers in the proxy request.

PoC by Grant Murphy

A proxy server on http://localhost:3000, using the following curl request will trigger the unhandled exception:

curl -XPOST http://localhost:3000 -d "$(python -c 'print("x"*1025)')"


Denial of Service (DoS) describes a family of attacks, all aimed at making a system inaccessible to its intended and legitimate users.

Unlike other vulnerabilities, DoS attacks usually do not aim at breaching security. Rather, they are focused on making websites and services unavailable to genuine users resulting in downtime.

One popular Denial of Service vulnerability is DDoS (a Distributed Denial of Service), an attack that attempts to clog network pipes to the system by generating a large volume of traffic from many machines.

When it comes to open source libraries, DoS vulnerabilities allow attackers to trigger such a crash or crippling of the service by using a flaw either in the application code or from the use of open source libraries.

Two common types of DoS vulnerabilities:

  • High CPU/Memory Consumption- An attacker sending crafted requests that could cause the system to take a disproportionate amount of time to process. For example, commons-fileupload:commons-fileupload.

  • Crash - An attacker sending crafted requests that could cause the system to crash. For Example, npm ws package