EUVD-2026-42435
GHSA-xg8h-3f4m-39v6
Severity by source
AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H
Attacker is an already-running low-privileged sandboxed process (AV:L, PR:L), no user interaction, and the sandbox-to-host break is a scope change (S:C) yielding full host C/I/A loss.
Primary rating from Vendor (ubuntu).
CVSS VectorVendor: ubuntu
Lifecycle Timeline
2DescriptionCVE.org
A sandbox escape vulnerability exists in the OpenJDK packages provided in Ubuntu. The .jar MIME handlers installed by these packages execute files marked as executable when the mailcap package is installed. A compromised or malicious sandboxed application with access to the OpenURI portal via xdg-desktop-portal-gtk can write a malicious .jar file to the host file system, set its executable bit, and trigger the handler to execute arbitrary code outside of the sandbox environment.
AnalysisAI
Sandbox escape in the OpenJDK packages shipped by Ubuntu allows a compromised sandboxed application to break out and run arbitrary code on the host. Because the packages' .jar MIME handlers execute any file flagged executable (when the mailcap package is present), an app abusing the OpenURI portal through xdg-desktop-portal-gtk can drop a malicious .jar, set its executable bit, and invoke the handler. There is no public exploit identified at time of analysis, but the flaw carries a CVSS 8.8 with a changed scope, reflecting full loss of host confidentiality, integrity and availability once the sandbox boundary is crossed.
Technical ContextAI
The issue lives at the intersection of the Linux desktop portal model and OpenJDK's Freedesktop integration. Ubuntu's OpenJDK packages register .jar (application/x-java-archive) MIME handlers via mailcap; those handler entries execute a file directly if its executable bit is set rather than treating the archive as inert data. xdg-desktop-portal-gtk's OpenURI portal is intended to let confined applications (e.g. Flatpak/Snap) ask the host to open a file or URI with the appropriate handler, mediating access across the sandbox boundary. Here the portal ends up invoking the OpenJDK .jar handler on attacker-controlled, executable-flagged content, converting a 'open this file' request into code execution. CWE-20 (Improper Input Validation) captures the root cause: the handler trusts the executable bit and MIME association without validating that launching the file is safe, and the portal does not prevent a confined app from writing and then executing host-side content. No CPE strings were supplied in the input, so exact package builds must be confirmed from the referenced Launchpad bug (openjdk-25 among the affected sources).
RemediationAI
No vendor-released patch identified at time of analysis; the only reference is the Ubuntu Launchpad tracking bug (https://bugs.launchpad.net/ubuntu/+source/openjdk-25/+bug/2153100), so monitor Ubuntu Security Notices for the fixed openjdk package versions and upgrade as soon as they publish. As compensating controls until a patch lands: remove or avoid installing the mailcap package on desktop systems where it is not required, which disables the .jar MIME handler behavior that makes the file executable (trade-off: other applications relying on mailcap MIME associations may lose default handler resolution); alternatively, remove or neuter the OpenJDK .jar handler entry so archives open as data rather than executing (trade-off: double-clicking .jar files will no longer launch them). Where feasible, restrict or disable the OpenURI capability of xdg-desktop-portal-gtk for untrusted sandboxed apps to close the write-and-trigger path (trade-off: confined apps lose the ability to hand files to host handlers). Ensure host filesystem locations writable by sandboxed apps do not permit setting the executable bit where possible.
Same weakness CWE-20 – Improper Input Validation
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