Old OpenSSL bug turns out to be a security issue (CVE-2016-2108)
Today OpenSSL released a security advisory. To my surprise one of the high severity issues involved a bug I had reported about a year ago.
The OpenSSL team didn't consider it to be a security issue - and neither did I. What I did back then was to find all possible inputs of the openssl command line tool and test them with american fuzzy lop, including those that very likely wouldn't have any security impact.
The feature I tested while finding this bug is part of the asn1 parser. It's actually not very well documented, but with openssl asn1parse -genconf [input] you can give OpenSSL a text file in a specific format that will then generate an ASN.1 structure. However it seems highly implausible that in any context one would use such a feature with attacker controlled input - therefore the bugs were fixed, but considered to be not security relevant.
But actually, the bug was not in the parser for that format itself. It was in an ASN.1 encoding function. Therefore applications that take ASN.1 encoded data and reencode it may trigger this code.
The bottom line is probably that we should be careful in claims that certain issues are not security relevant. The good news is that OpenSSL fixed this issue anyway, so all versions since June 2015 are safe.
The OpenSSL team didn't consider it to be a security issue - and neither did I. What I did back then was to find all possible inputs of the openssl command line tool and test them with american fuzzy lop, including those that very likely wouldn't have any security impact.
The feature I tested while finding this bug is part of the asn1 parser. It's actually not very well documented, but with openssl asn1parse -genconf [input] you can give OpenSSL a text file in a specific format that will then generate an ASN.1 structure. However it seems highly implausible that in any context one would use such a feature with attacker controlled input - therefore the bugs were fixed, but considered to be not security relevant.
But actually, the bug was not in the parser for that format itself. It was in an ASN.1 encoding function. Therefore applications that take ASN.1 encoded data and reencode it may trigger this code.
The bottom line is probably that we should be careful in claims that certain issues are not security relevant. The good news is that OpenSSL fixed this issue anyway, so all versions since June 2015 are safe.
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