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CVE-2026-104476 – Sensitive Configuration Disclosure – Backdrop CMS before 1.35.1 (and 1.34.x before

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Summary

CVE-2026-104476 is an information disclosure vulnerability in Backdrop CMS affecting versions before 1.35.1 (and 1.34.x before 1.34.5). When a user with permission to synchronize, import, and export configuration performs a configuration export, Backdrop CMS leaves the resulting compressed configuration archive accessible on the server after it has been transferred to the user. An unauthenticated remote attacker who locates this archive can download it and obtain sensitive site configuration data. The issue is tracked under CWE-200 (Exposure of Sensitive Information to an Unauthorized Actor) and has been assigned a CVSS v4.0 score of 8.2 (High).

Technical details

  • Root cause: After generating a configuration export archive for download, Backdrop CMS core does not remove the compressed archive file from the server’s file system once the transfer to the requesting user completes.
  • Trigger conditions: A site user holding the "Synchronize, import, and export configuration" permission must first perform a configuration export, which creates the leftover archive; no further authenticated action by the attacker is required.
  • Attack vector: Network-based and unauthenticated — once the archive exists on the server, any remote party who can locate or guess its path can retrieve it directly over HTTP(S).
  • Impact: Exposure of the site’s exported configuration, which can include sensitive settings and structural details about the site, with no corresponding impact on integrity or availability.

Affected software

  • Backdrop CMS core 1.35.x prior to 1.35.1
  • Backdrop CMS core 1.34.x prior to 1.34.5
  • Versions 1.33 and earlier are outside the vendor’s current security support window

Severity

  • CVSS v4.0: 8.2 (High) — CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N
  • CVSS v3.1: 5.9 (Medium) — CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N

Mitigation and recommended actions

  • Immediate: Upgrade to Backdrop CMS core 1.35.1 (sites unable to move to the 1.35.x branch should at minimum apply the 1.34.5 security release). Follow the vendor’s documented core update procedure after upgrading.
  • If immediate patching is not possible: Restrict or audit who holds the "Synchronize, import, and export configuration" permission to limit when leftover export archives are created, and review the server’s file system/web-accessible directories for any residual configuration export archives and remove them manually. Subscribe to Backdrop security advisory notifications to be alerted to future releases addressing this issue.

References

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