Malicious Sicoob NuGet Steals Banking Credentials as npm Packages Target Cloud Secrets
May 29, 2026
Software Supply Chain / Threat Intelligence
Cybersecurity researchers have discovered a malicious NuGet package that masquerades as a C# software development kit for Sicoob, one of Brazil's largest cooperative financial systems, to siphon client IDs and PFX certificates. According to Socket , versions 2.0.0 through 2.0.4 of " Sicoob.Sdk " contain functionality to exfiltrate sensitive information, including PFX certificates that are used to authenticate businesses with the Sicoob banking network in order to automate banking operations, such as processing instant payments and generating dynamic Pix QR codes. The package is estimated to have been downloaded nearly 500 times. "When a developer instantiates SicoobClient with a client ID, a PFX file path, and a PFX password, the package reads the PFX file from disk, Base64-encodes its contents, and sends the supplied client ID, PFX password, and encoded PFX data to a hardcoded third-party Sentry endpoint," security researcher Kirill Boychenko said. In ad...