Scans hit new Atlassian traversal flaw CVE-2026-21589
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Attackers are actively scanning for a newly patched Atlassian arbitrary file-read vulnerability using public PoC exploit paths from Watchtowr.
Atlassian released patches on October 5th for an arbitrary file access vulnerability (CVE-2026-21589) affecting multiple Atlassian products. The flaw is a directory traversal issue with an unusual twist: Atlassian's web application replaces path separators with the string "::" to prevent traversal, but certain request patterns cause this escaping to be reversed, allowing the "::" sequences to be translated back to "/" on the server and enabling path traversal outside the intended resource directory. Watchtowr published a detailed write-up including proof-of-concept exploit URLs.
SANS ISC observed exploit attempts hitting its honeypots within a day of the Watchtowr disclosure, using the exact PoC URL patterns from that blog post. The exploit targets static resource download endpoints across Jira, Bitbucket, and Confluence, appending traversal sequences to reach files like WEB-INF/web.xml — a file guaranteed to exist in any Tomcat-based deployment and therefore useful to confirm successful traversal, analogous to /etc/passwd on Linux. Note that /etc/passwd itself is not reachable, as access remains constrained to the web application's own directory; only files within that directory tree, such as configuration files, are exposed. Based on timing and the specific endpoints targeted, the ISC author believes a single threat actor is behind the observed scanning, though the actor is not named or attributed. All 13 observed source IPs are hosted on DigitalOcean infrastructure.
Defenders running Atlassian Jira, Bitbucket, or Confluence should apply the October 5th patches immediately, review web server/application logs for requests containing repeated "..::" sequences targeting /download/resources/ or /s/*/_/download/resources/ paths, and treat any hits against the listed DigitalOcean IPs as exploitation attempts against this vulnerability.
Mentioned in this report
Source reporting: https://isc.sans.edu/diary/rss/33406
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