Monero [XMR] witnesses vulnerability in its accounting functionality, patch released by handler

On 5th September, Monero released a report in which they announced a post mortem of the multiple counting bug that they faced recently. The report provided a detailed information about the bug and how it was used to exploit services, merchants and exchanges.

The multiple counting bug had two variants, which required a different structure of the transaction public key. It was introduced in conjunction with the subaddress feature.

In the first variant of the bug, the code did not impose an inspection to guard against duplicate public keys. This vulnerability resulted in attackers creating a transaction in which the transaction public key would be included multiple times. This resulted in the duplication of the particular transaction public key.

In the second variant of the bug, the code did not impose a check against dummy transaction public keys. Therefore, a hacker could trick the wallet into scanning the outputs in a transaction twice by utilizing the alternative transaction public key feature. As a result, the receiving wallet would report that it had received two times the amount that it had actually received.

The first variant of the bug was earlier reported on GitHub, and the severity of the bug was underestimated. This resulted in the exploitation of exchanges, and funds being stolen from organizations in the Monero ecosystem.

Moreover, a security researcher for HackerOne provided an elaborate report on how the bug was being utilized to steal funds from exchanges. The second variant of the bug was reported by Phiren on HackerOne.

After merging both the patches, Fluffypony, Monero’s Lead Maintainer released a new version V0.12.3.0. The severity of a critical bug in the wallet software was initially underestimated which allowed an attacker to steal funds from organizations in the Monero ecosystem.

Fortunately, the bug was confined to the accounting functions of the wallet software, and thus the protocol and coin supply were not affected. The Monero community also spoke about the adequate measures taken to solve the problem. DubsNC stated on Reddit:

“Yeah, the mailing list doesn’t sound like a good idea to me. It does sound like a high value target list for an adversary. How about just a signed update flag in the protocol that tells all full nodes to update at the sale time?”

Flenst, an enthusiastic Redditor stated:

“I am really glad to see that mistakes that have been done won’t be repeated and there will be better solutions in the future to disclose vulnerabilities like this to services in a more reliable way.”