Bug 2538186 (CVE-2026-62943)

Summary: CVE-2026-62943 btrbk: btrbk: Arbitrary Command Execution via SSH Command Filter Bypass
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
Status: NEW --- QA Contact:
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Priority: high    
Version: unspecifiedKeywords: Security
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Hardware: All   
OS: Linux   
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A flaw was found in btrbk. btrbk's ssh_filter_btrbk.sh script, used for creating snapshots and remote backups of Btrfs subvolumes, constructs an allowlist with an incomplete command match. This allows a user, restricted through an authorized_keys forced command, to append additional commands after a valid btrbk command prefix. This bypasses the intended security restrictions, leading to arbitrary command execution with the privileges of the backup-target SSH account. Deployments that do not use ssh_filter_btrbk.sh in authorized_keys are not affected.
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Description OSIDB Bzimport 2026-09-22 17:24:01 UTC 
btrbk is a tool for creating snapshots and remote backups of Btrfs subvolumes. From 0.29.0 until 0.32.7, btrbk's ssh_filter_btrbk.sh constructs allow_stream_match with a start anchor but without an end-of-string anchor for the complete command. A user restricted through an authorized_keys forced command can append a trailing pipe command after a valid btrbk command prefix, bypassing the allowlist and executing arbitrary commands with the privileges of the backup-target SSH account. Deployments that do not use ssh_filter_btrbk.sh in authorized_keys are not affected. This issue is fixed in version 0.32.7.