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Message-ID: <CAHJtQJ5J4vqOhHb1juebcaNf1HOybhv4zueGmEAGDYnsEbwDMQ@mail.gmail.com>
Date: Fri, 28 Nov 2014 09:36:04 -0800
From: Ingy dot Net <ingy@...y.net>
To: John Haxby <john.haxby@...cle.com>
Cc: oss-security@...ts.openwall.com, Kirill Simonov <xi@...olvent.net>,
Ingy döt Net <ingy@...n.org>
Subject: Re: libyaml / YAML-LibYAML DoS
I have fixed this by commenting out the assert. This makes the parser fail
as it should.
I've pushed the patch to the git-hub mirror of libyaml:
https://github.com/yaml/libyaml
I've added a test to https://metacpan.org/release/YAML-LibYAML and released
version 0.53.
Ingy
PS Here is the Perl minimum test case, with the patched behavior:
$ perl -MYAML::XS -e 'Load qq! x: "\n"x!'
YAML::XS::Load Error: The problem:
did not find expected key
was found at document: 1, line: 2, column: 2
while parsing a block mapping at line: 1, column: 2
On Fri, Nov 28, 2014 at 7:45 AM, Ingy dot Net <ingy@...y.net> wrote:
> Taking a look at this now. Please let me know if you've already found a
> patch.
>
> Ingy
>
> On Fri, Nov 28, 2014 at 2:20 AM, John Haxby <john.haxby@...cle.com> wrote:
>
>> On 28/11/14 05:57, Jonathan Gray wrote:
>> > libyaml and the perl YAML-LibYAML (aka YAML-XS) module based
>> > on the same code have an "impossible" assert that can be
>> > triggered with the following yaml. This is a reduced testcase
>> > of a crash found with the afl fuzzer.
>> >
>> > a: "
>> > " b: true
>> >
>> > In other words a crash/denial of service with untrusted yaml input.
>> > The libyaml author was contacted on the 21st and 27th of November.
>> > No response has been received but the issue has independently been
>> > reported publically since:
>> >
>> https://bitbucket.org/xi/libyaml/issue/10/wrapped-strings-cause-assert-failure
>> >
>> > [1] Parsing 'test.yaml': assertion "parser->simple_key_allowed ||
>> !required" failed: file "scanner.c", line 1113, function
>> "yaml_parser_save_simple_key"
>> >
>> > assert(parser->simple_key_allowed || !required); /* Impossible. */
>>
>> For what it's worth PyYAML 3.10 and 3.11 have exactly the same assertion:
>>
>> >>> import yaml
>> >>> yaml.load("""
>> ... abc:
>> ... def: 'xxx
>> ... ' ghi: 'yyy'
>> ... """)
>> Traceback (most recent call last):
>>
>> [...]
>>
>> assert self.allow_simple_key or not required
>> AssertionError
>>
>> jch
>>
>
>
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