A security researcher from Colombia has found a way of assigning admin rights and gaining boot persistence on Windows PCs that’s simple to execute and hard to stop –all the features that hackers and malware authors are looking for from an exploitation technique.

What’s more surprising, is that the technique was first detailed way back in December 2017, but despite its numerous benefits and ease of exploitation, it has not received either media coverage nor has it been seen employed in malware campaigns.

Discovered by Sebastián Castro, a security researcher for CSL, the technique targets one of the parameters of Windows user accounts known as the Relative Identifier (RID).

The RID is a code added at the end of account security identifiers (SIDs) that describes that user’s permissions group. There are several RIDs available, but the most common ones are 501 for the standard guest account, and 500 for admin accounts.

Image: Sebastian Castro

Castro, with help from CSL CEO Pedro García, discovered that by tinkering with registry keys that store information about each Windows account, he could modify the RID associated with a specific account and grant it a different RID, for another account group.

The technique does not allow a hacker to remotely infect a computer unless that computer has been foolishly left exposed on the Internet without a password.

But in cases where a hacker has a foothold on a system –via either malware or by brute-forcing an account with a weak password– the hacker can give admin permissions to a compromised low-level account, and gain a permanent backdoor with full SYSTEM access on a Windows PC.

Since registry keys are also boot persistent, any modifications made to an account’s RID remain permanent, or until fixed.

The attack is also very reliable, being tested and found to be working on Windows versions going from XP to 10 and from Server 2003 to Server 2016, although even older versions should be vulnerable, at least in theory.

“It is not so easy to detect when exploited, because this attack could be deployed by using OS resources without triggering any alert to the victim,” Castro told ZDNet in an interview last week.

“On the other hand, I think is easy to spot when doing forensics operations, but you need to know where to look at.

“It is possible to find out if a computer has been a victim of RID hijacking by looking inside the [Windows] registry and checking for inconsistencies on the SAM [Security Account Manager],” Castro added.

Source: Researcher finds simple way of backdooring Windows PCs and nobody notices for ten months | ZDNet