Bug 2531818

Summary: CVE-2026-77159 libvirt: Unsafe chown in qemuTPMEmulatorPrepareHost() allows arbitrary file ownership change via symlink [fedora-all]
Product: [Fedora] Fedora Reporter: Mauro Matteo Cascella <mcascell>
Component: libvirtAssignee: Fedora Virtualization Maintainers <virt-maint>
Status: NEW --- QA Contact: Fedora Extras Quality Assurance <extras-qa>
Severity: medium Docs Contact:
Priority: medium    
Version: rawhideCC: berrange, clalancette, crobinso, jforbes, jiyin, laine, libvirt-maint, suraj.ghimire7, virt-maint
Target Milestone: ---Keywords: Security, SecurityTracking
Target Release: ---   
Hardware: Unspecified   
OS: Unspecified   
Whiteboard: {"flaws": ["4b26f56c-f480-4cb1-8dc9-adbc2569dca5"]}
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oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: --- Target Upstream Version:
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Bug Depends On:    
Bug Blocks: 2531811    

Description Mauro Matteo Cascella 2026-09-11 10:08:06 UTC 
Disclaimer: Community trackers are created by Red Hat Product Security team on a best effort basis. Package maintainers are required to ascertain if the flaw indeed affects their package, before starting the update process.

A symlink-following flaw was found in libvirt's qemuTPMEmulatorPrepareHost() function (src/qemu/qemu_tpm.c). The function uses a path-based chown() to set ownership of the swtpm logfile without verifying that the path is not a symbolic link. Since the log directory is writable by the swtpm user, a local attacker with access to the swtpm account can replace the logfile with a symlink pointing to an arbitrary file. When libvirtd (running as root) starts a QEMU domain with an emulated TPM, it follows the symlink and transfers ownership of the target file to swtpm:swtpm, allowing the attacker to then modify that file.

The upstream fix replaces the path-based chown() with open(O_NOFOLLOW) + fchown() on the file descriptor.

External reference: https://gitlab.com/libvirt/libvirt/-/work_items/909