A vulnerability in Ubuntu’s OpenJDK packages allows an attacker to escape a sandboxed application by creating an executable .jar file on the host system. When the mailcap package is present, the operating system automatically executes .jar files that have the executable bit set. This improper input validation (CWE‑20) enables an attacker to run arbitrary code outside the sandbox, potentially leading to full system compromise. The flaw requires the exploit chain to involve a malicious or compromised sandboxed application that can access the OpenURI portal via xdg-desktop-portal-gtk to write the malicious archive to disk.

Any Ubuntu installation containing the OpenJDK packages together with the mailcap package and the xdg-desktop-portal-gtk component is affected. No specific package version range is provided, so the vulnerability applies to any such installation.

The vulnerability carries a CVSS score of 8.8, indicating high severity, while the EPSS score of <1% suggests a very low probability of exploitation at present, and it has not been listed in the CISA KEV catalog. The likely attack path involves a sandboxed application with OpenURI portal access that writes a malicious .jar file to the host file system, marks it executable, and then triggers the system’s MIME handler to execute it, thereby bypassing the sandbox and granting the attacker arbitrary code execution on the host.