One of the teams security of Google he said that he discovered a kind of malware that abuses a new technique to avoid detection by security products by cleverly modifying the digital signature of its files.
It was discovered by Neel Mehta, a security researcher in the Google Threat Analysis Group (TAG from Threat Group). This technique was used by an adware strain called OpenSUpdater.
In the samples, the digital signature was processed and the End of Content (EOC) flag was changed to a NULL tag in the “parameters” element of the SignatureAlgorithm that signs the X.509 leaf certificate. EOC pointers terminate encodings of indefinite length, but in this case EOC usesfor the encoding of a certain length (l=13).
The technical explanation given by the researcher is a bit difficult to understand by users who do not know, but Mehta refers to a small edit made by the developers of OpenSUpdater in a small field within the digital signature of its payloads.
On Windows systems, this small edit does not show the signature controls of an operating system file, which makes the malware invisible. This allows him to run without safety warnings.
Mehta states that security products, which use the bibliographycase OpenSSL to parse and extract a file's signature information, will fail to scan files whose digital signature has been modified by this method.
"This is the first time TAG has discovered hackers who use this technique to avoid detection while maintaining a valid digital signature on PE files," Mehta said today.
The Google researcher contacted Microsoft, and reported the security gap to change them algorithms of the control of digital signatures.
Files infected with OpenSUpdater adware are currently distributed via cracked games and software.
Once it infects a system, adware is used to download and install unwanted software.
Google reports that most victims of OpenSUpdater are in the United States.