Incomplete validation of an S3 object key returned by a configured S3 endpoint allowed an attacker with control over the S3 server to overwrite arbitrary host paths as user/group backup when an S3-refresh is triggered.
This issue was reported privately by Project Loupe.
An attacker with direct access to a PBS datastore configured as storage on a Proxmox VE host can construct and upload a malicious pxar archive with two root entries.
When such a backup archive was restored by pve-container, the archive contents were written outside of the target rootfs mountpoint. If a container is restored as privileged container, the extraction runs as root.
proxmox-backup-client will now refuse to follow symlinks during extraction of directories or hardlinks.
This issue was reported privately by Project Loupe.
Subject: PSA-2026-00061-1: Missing validation of chunk sizes during pull sync
Advisory date: 2026-10-07
Packages: proxmox-backup-server
Details:
An attacker with control over a pull source (or its raw index contents) could trick the pull target into storing an index file with an invalid reference to a valid chunk. Subsequent verification of that index will treat the chunk as corrupt, breaking availability of other valid snapshots referencing it.
This issue was reported privately by Project Loupe.
Subject: PSA-2026-00086-1: Missing protections against bogus snapshot creation
Advisory date: 2026-11-10
Packages: proxmox-backup-server
Details:
An attacker that only has "Datastore.Backup" privileges on a datastore could create bogus snapshots in a group they own. Independently executed prune tasks (such as by a scheduled job or administrator with higher privileges) would treat such bogus snapshots as legitimate.
These two issues combined could be exploited to trigger a pruning of all legitimate snapshots in such an accessible group, thwarting the ransomware protection guards usually associated with only giving "Datastore.Backup" privileges to a user/token.
Creating such bogus snapshots is now restricted.
These issues were discovered internally, and independently reported by Richard DEMONGEOT - Rdem Systems <richard@rdem-systems.com>.
Subject: PSA-2026-00087-1: Missing privilege check in sync-job modification allows denial of service
Advisory date: 2026-11-10
Packages: proxmox-backup-server
Details:
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.
