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CVE-2026-21589 – Unauthenticated Path Traversal / Arbitrary File Read – Atlassian Bamboo (All Versio

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Summary

CVE-2026-21589 is a critical path traversal vulnerability affecting Atlassian Bamboo Data Center and Server (along with several other Atlassian Data Center/Server products). An unauthenticated remote attacker who knows the exact name and path of a target file can retrieve files from within the web application root directory. Atlassian rates this vulnerability as Critical with a CVSS score of 9.3.

Technical details

  • Root cause: Atlassian Bamboo fails to properly sanitize or restrict file path input, allowing path traversal sequences to escape the intended directory and access files within the web application root.
  • Trigger conditions: Exploitation requires the attacker to have prior knowledge of the exact target file’s name and path; the vulnerability does not allow directory listing or enumeration of arbitrary file names.
  • Attack vector: Network-based and does not require authentication or any user interaction, making the vulnerability remotely exploitable against any internet-exposed Bamboo instance.
  • Impact: Successful exploitation results in unauthorized read access (high confidentiality impact) to files within the application root, which may expose sensitive configuration data, credentials, or other application files depending on the specific files targeted.

Affected software

  • Bamboo Data Center: All versions prior to 10.2.24 and 12.1.12
  • Bamboo Server: All versions (Server editions are past end of life and will not receive a fix)

Note: This path traversal issue was addressed by Atlassian across multiple Data Center/Server products in the same product line, including Bitbucket, Confluence, Crowd, Crucible, Fisheye, Jira Software, and Jira Service Management. This post focuses specifically on the Bamboo impact.

Severity

  • CVSS Score: 9.3 (Critical)
  • CVSS Vector (v4.0): CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:N/VA:N/SC:H/SI:H/SA:H

Note: Atlassian published this vulnerability using the CVSS v4.0 standard; no CVSS v3.1 vector has been issued for this CVE.

Mitigation and recommended actions

  • Immediate: Upgrade Bamboo Data Center to version 10.2.24, 12.1.12, or later, which contain the fix for this vulnerability.
  • If no patch can be applied immediately:
    • Bamboo Server is past end of life and will not receive a patch — organizations still running Bamboo Server should plan migration to a supported Data Center release.
    • Restrict or disconnect internet-facing access to the Bamboo instance where feasible.
    • Deploy Web Application Firewall (WAF) rules to detect and block path traversal patterns, such as ".." sequences adjacent to forward or backward slashes, in incoming requests.
    • Monitor web server and application logs for anomalous requests containing directory traversal sequences targeting known sensitive file paths.

References

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