PSA-2026-00087: Proxmox Backup Server: Missing privilege check in sync-job modification allows denial of service
This Proxmox advisory covers a security issue in Proxmox Backup Server.
Key facts
- Fixed in
- proxmox-backup-server 4.2.9-1
- Advisory id
- PSA-2026-00087
- Source published
- Listed by VulniPulse
Compiled by VulniPulse from the linked sources. How records are collected and checked.
Affected products & platforms
Description
A missing check for the current owner allowed a different user to take over a sync-job by pointing source and target to datastores or namespaces they have access to, effectively removing the sync-job for the original owner.
The effect is limited to a denial of service, no access to or exfiltration of data that the attacker is not allowed to access is possible. An attacker would also need to guess or know the job id for modification, which is random by default.
The issue was privately reported by Yuliang Xiao. Packages: proxmox-backup-server.
Text from the source record.
Fix and mitigation
Upgrade to a fixed release named by Proxmox:
- proxmox-backup-server 4.2.9-1
Vendor guidance
- Update to the fixed package versions: proxmox-backup-server >= 4.2.9-1.
End-of-life dates for Proxmox Backup Server
More Proxmox advisories
PSA-2026-00099Nov 10, 2026Proxmox: Incomplete validation of UPID when handling "stop task" API requestsPSA-2026-00086Nov 10, 2026Proxmox Backup Server: Missing protections against bogus snapshot creationPSA-2026-00062Oct 7, 2026Proxmox Backup Server: Missing privilege checksPSA-2026-00061Oct 7, 2026Proxmox Backup Server: Missing validation of chunk sizes during pull syncPSA-2026-00060Oct 7, 2026Proxmox Backup Server: Missing privilege checks when removing namespace from prune jobPSA-2026-00059Oct 7, 2026Proxmox Backup Server: pxar/container restore target rootfs escape
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