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 >> > >> >  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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