Malicious Python Package uses Unicode support to evade detection

Researchers discovered a malicious package on PyPI that uses Unicode to evade detection while stealing sensitive data.

Supply chain security firm Phylum discovered a malicious Python package on the Python Package Index (PyPI) repository that uses Unicode to evade detection and deliver information-stealing malware.

The package, named onyxproxy, was uploaded to the PyPI repository on March 15, 2023. The analysis of the package revealed that it supports data harvesting capabilities.

“Phylum’s automated platform recently detected the onyxproxy package on PyPI, a malicious package that harvests and exfiltrates credentials and other sensitive data. In many ways, this package typifies other token stealers that we have found prevalent in PyPI.” reads the analysis published by Phylum.”However, one feature of this particular package caught our eye: an obfuscation technique that was foreseen in 2007 during a discussion about Python’s support for Unicode, documented in PEP-3131

While inspecting the code the experts multiple strange, non-monospaced, sans-serif font with mixed bold and italics. The attackers used Unicode variants of characters that appear identical to a human inspection (homoglyphs) (i.e., self vs. 𝘀𝘦𝘭𝘧). The attackers used this trick to evade detection, but when the Python interpreter parsed the code the malicious code was executed.

“An obvious and immediate benefit of this strange scheme is readability. We can still easily reason about this code, because our eyes and brains can still read the words, despite the intermixed fonts. Moreover, these visible differences do not prevent the code from running, which it does.” continues the analysis. “One might dismiss this as a developer trying to show how clever they can be, except that this package is trying to steal and exfiltrate things immediately upon installation.”

A similar technique was detailed by the researchers Nicholas Boucher and Ross Anderson, who explained how to abuse bidirectional override characters and homoglyphs in a variety of programming languages.

The experts pointed out that the author of onyxproxy demonstrates is not sophisticated, he likely merely cut-and-paste code from various sources and put them together. This obfuscation technique is absent from other parts of the code in and many Python modules are imported multiple times.

“But, whomever this author copied this obfuscated code from is clever enough to know how to use the internals of the Python interpreter to generate a novel kind of obfuscated code, a kind that is somewhat readable without divulging too much of exactly what the code is trying to steal.” concludes the report. “This novelty is something that we will be keeping an eye on at Phylum, because now that this technique has proven viable in the wild, we fully anticipate others to copy and improve their attempts to attack developers.”

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Pierluigi Paganini

(SecurityAffairs – hacking, Python)

Pierluigi Paganini

Pierluigi Paganini is member of the ENISA (European Union Agency for Network and Information Security) Threat Landscape Stakeholder Group and Cyber G7 Group, he is also a Security Evangelist, Security Analyst and Freelance Writer. Editor-in-Chief at "Cyber Defense Magazine", Pierluigi is a cyber security expert with over 20 years experience in the field, he is Certified Ethical Hacker at EC Council in London. The passion for writing and a strong belief that security is founded on sharing and awareness led Pierluigi to find the security blog "Security Affairs" recently named a Top National Security Resource for US. Pierluigi is a member of the "The Hacker News" team and he is a writer for some major publications in the field such as Cyber War Zone, ICTTF, Infosec Island, Infosec Institute, The Hacker News Magazine and for many other Security magazines. Author of the Books "The Deep Dark Web" and “Digital Virtual Currency and Bitcoin”.

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