SzafirHost verifies the signature of a downloaded JAR file using JarInputStream, which reads from the beginning of the file, but then loads classes with JarFile/URLClassLoader, which reads the Central Directory from the end. This mismatch allows an attacker to append malicious ZIP entries to a legitimate signed JAR, causing the signature check to succeed while the malicious class is loaded. The attacker can thus achieve remote code execution within the host JVM, potentially compromising integrity and confidentiality of the affected system.

Vulnerable product is SzafirHost provided by Krajowa Izba Rozliczeniowa. The flaw is present in all releases prior to 1.2.1. No specific patch version is listed beyond the note that version 1.2.1 contains the fix.

CVSS score of 8.6 indicates a high severity. EPSS score is not available, so exploitation probability is unknown, but the vulnerability is not listed in CISA’s KEV catalog. The attack path likely needs delivery of a crafted JAR to the application, implying supply‑chain or insider threat vectors. Once the malicious class is loaded, it could execute arbitrary code with the privileges of the JVM process, making the risk serious for systems that run SzafirHost with untrusted code.