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CVE Record

CVE-2021-38173: Btrbk before 0.31.2 allows command execution because of the mishandling of remote hosts filtering SSH comma...

Btrbk before 0.31.2 allows command execution because of the mishandling of remote hosts filtering SSH commands using ssh_filter_btrbk.sh in authorized_keys.

UnknownCVSS not scoredNot KEV-listedUpdated
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Glexia's TakeAutomated analysismoderate

Security readout for executives and security teams

Plain-English summary

Btrbk versions before 0.31.2 can allow command execution when its SSH command filter is used for remote backup access. The issue is narrow but serious for systems relying on authorized_keys restrictions to safely delegate backup operations.

Executive priority

Prioritize remediation where btrbk is used for remote backups with SSH key restrictions. Business impact could include unauthorized command execution on backup infrastructure, but current sources do not support emergency treatment absent exposed or high-trust deployments.

Technical view

The vulnerability is in ssh_filter_btrbk.sh, used with authorized_keys to filter SSH commands for remote btrbk operations. Sources describe mishandling of remote host filtering, which can permit command execution outside the intended restriction. Fixed upstream version is 0.31.2.

Likely exposure

Exposure is most likely on systems running btrbk before 0.31.2 and using ssh_filter_btrbk.sh in authorized_keys for remote hosts. Debian LTS and Fedora issued security updates, indicating packaged Linux deployments may be affected.

Exploitation context

The provided sources do not show active exploitation, and the CVE is not listed as KEV. The attack context appears tied to configured SSH-based remote backup access, not a default internet-facing service. Evidence is incomplete on prerequisites and exploit prevalence.

Researcher notes

Key facts come from the CVE record, upstream commit, changelog, and Debian/Fedora advisories. CVSS, CWE, detailed affected CPEs, and exploitation evidence are not supplied in the bundle, so risk scoring should be adjusted after local configuration review.

Mitigation direction

  • Upgrade btrbk to version 0.31.2 or later.
  • Apply relevant Debian LTS or Fedora security updates.
  • Review authorized_keys entries using ssh_filter_btrbk.sh.
  • Check upstream and distribution advisories for environment-specific guidance.
  • Restrict backup SSH keys and accounts to necessary hosts only.

Validation and detection

  • Inventory installed btrbk versions across backup systems.
  • Identify authorized_keys entries invoking ssh_filter_btrbk.sh.
  • Confirm distro package versions include the security fix.
  • Review backup SSH accounts for unexpected command permissions.
  • Check logs for unusual backup-user SSH activity.
Prepared
Confidence
medium
Sources
7

Public sources used

Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.

Potential ATT&CK relevance

Conservative CVE-to-ATT&CK context

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CVE-2021-38173 mapping review

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Vulnerability profileCVE Program record
Severity
Unknown
CVSS
Not scored
Known Exploited
No
Published
Official CVE source material

CNA and ADP enrichment extracted from CVE v5

These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.

0CVSS vectors
0Timeline events
0ADP providers
6Source links

CVSS and timeline data

No CVSS vectors or timeline events were available in the normalized CVE source material.

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
n/an/an/aListed
Weakness

CWE details

No CWE listed

CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.