Detect CVE-2026-21589: Atlassian Arbitrary File Access Across Multiple Products in Sumo Logic CSE
Detects exploitation of CVE-2026-21589, a CWE-552 arbitrary file access / path traversal vulnerability impacting multiple Atlassian products (Confluence, Jira, Bitbucket, Bamboo). An unauthenticated or low-privileged external party can request files and directories outside the intended web root, exposing sensitive configuration files, credentials, and secrets. The vulnerability is on the CISA KEV catalog (disclosed 2026-10-15) and is covered by CISA BOD 26-04. This detection surfaces anomalous HTTP requests containing traversal sequences, encoded path separators, and access to sensitive filesystem paths against Atlassian application endpoints, plus resulting filesystem access by the Atlassian service account.
MITRE ATT&CK
- Tactic
- Initial Access Collection
Sumo Detection Query
_sourceCategory=*web* OR _sourceCategory=*proxy*
| parse regex "(?<method>\S+)\s(?<url>\S+)\sHTTP" nodrop
| where url matches /.*\/(confluence|jira|bitbucket|bamboo|rest|plugins\/servlet)\/.*/
| where url matches /(?i)(\.\.%2f|\.\.\/|\.\.%252f|\.\.%5c|%2e%2e|WEB-INF|confluence\.cfg\.xml|dbconfig\.xml|\/etc\/passwd)/
| count as hits by src_ip, url, status_code
| where hits >= 1
| sort by hitsSumo Logic query surfacing Atlassian endpoint requests with traversal or sensitive-file patterns indicative of CVE-2026-21589 arbitrary file access.
Data Sources
Required Tables
False Positives & Tuning
- Scheduled authorized vulnerability assessments
- Encoded URLs from legitimate API consumers
- CDN or WAF rewrite artifacts that inject encoded characters
Other platforms for CVE-2026-21589
Testing Methodology
Validate this detection against 3 adversary techniques from Atomic Red Team. Each test below lists the behaviour to exercise and the telemetry you should expect to see. Executable commands and cleanup steps are available with Pro.
- Test 1 Confluence config file access via encoded traversal
Expected signal: Web/reverse-proxy access log entry for the lab host showing a request containing '..%2f' sequences and 'confluence.cfg.xml'.
- Test 2 Jira WEB-INF resource disclosure attempt
Expected signal: Access log entry with double-encoded '%252f' traversal targeting a /jira/rest/ path and WEB-INF.
- Test 3 etc passwd read attempt on Windows host
Expected signal: W3CIISLog / reverse-proxy entry showing '..%2f' traversal toward '/etc/passwd' on a /bamboo/ path.
References (4)
- https://confluence.atlassian.com/security/cve-2026-21589-arbitrary-file-access-vulnerability-impacts-multiple-products-1870495748.html?ref=labs.watchtowr.com
- https://www.cisa.gov/news-events/directives/bod-26-04-prioritizing-security-updates-based-risk
- https://www.cisa.gov/news-events/directives/bod-26-04-implementation-guidance-prioritizing-security-updates-based-risk
- https://nvd.nist.gov/vuln/detail/CVE-2026-21589
Response Playbook
Triage
- Confirm the targeted host runs an affected Atlassian product (Confluence, Jira, Bitbucket, or Bamboo) and identify its current version against the Atlassian CVE-2026-21589 advisory.
- Reconstruct the full decoded request URL(s) from the source IP and determine which file(s) or directories were requested (e.g., confluence.cfg.xml, dbconfig.xml, /etc/passwd, WEB-INF resources).
- Check the HTTP response/status codes — a 200 with a non-trivial response size indicates successful file disclosure rather than a blocked probe.
- Determine whether the source IP is internal (authorized scanner) or external/unrecognized, and correlate against threat-intel for known CVE-2026-21589 exploitation infrastructure.
Containment
- Apply the Atlassian vendor patch for CVE-2026-21589 to all affected products immediately, per CISA BOD 26-04 prioritization.
- If patching cannot be immediate, block the vulnerable traversal patterns at the WAF/reverse proxy and restrict external access to the affected Atlassian instance.
- Block the identified malicious source IP(s) at the perimeter firewall and WAF.
Evidence Collection
- Preserve web server / reverse proxy access logs covering the full exploitation window, including decoded request URLs and response sizes.
- Capture the Atlassian application logs (catalina.out, atlassian-confluence.log, application.log) and a copy of any configuration files that may have been disclosed.
Escalation Criteria
- !Escalate to incident response if any request returned HTTP 200 with content indicating successful disclosure of credentials, dbconfig.xml, or confluence.cfg.xml.
- !Escalate immediately if post-access activity (new admin accounts, database connections from the disclosed credentials, or lateral movement) is observed, as disclosed secrets may enable full compromise.
Investigation Guide
Related Techniques
Forensic Artifacts
- >
Web/reverse-proxy access log entries with traversal sequences and the associated response sizes - >
Atlassian application and Tomcat logs (catalina.out, atlassian-confluence.log) - >
Timestamps and byte counts of accessed configuration files (confluence.cfg.xml, dbconfig.xml) on the filesystem
Tuning Guidance
Whitelist IP ranges of authorized internal vulnerability scanners and DAST tooling to reduce benign traversal-probe noise. Prioritize alerts where the HTTP status is 200 and the response size is non-trivial, since blocked or 404 probes are far lower fidelity. If the organization fronts Atlassian with a WAF that normalizes URLs, baseline encoded-character usage from legitimate API integrations before enabling high-severity paging, and tighten the sensitive-file regex list to the specific products deployed.
Hunting Queries
Hunts for successful (HTTP 200) disclosures of sensitive Atlassian configuration files over the past 30 days, ranked by response size to surface actual data exfiltration versus blocked probes.
W3CIISLog | where TimeGenerated > ago(30d) | extend dec = url_decode(strcat(csUriStem, csUriQuery)) | where dec has_any ("confluence.cfg.xml","dbconfig.xml","/WEB-INF/","/etc/passwd") | where scStatus == 200 | project TimeGenerated, cIP, csUriStem, scStatus, scBytes | order by scBytes descindex=web (sourcetype=iis OR sourcetype=access_combined) | eval dec=urldecode(uri_query) | search (dec="*confluence.cfg.xml*" OR dec="*dbconfig.xml*" OR dec="*/WEB-INF/*" OR dec="*/etc/passwd*") status=200 | stats count values(bytes) AS resp_bytes by src_ip, uri_path | sort - resp_bytesAtomic Red Team Tests
Simulates CVE-2026-21589 by requesting the Confluence configuration file through an encoded path-traversal sequence against a lab Atlassian endpoint.
Command
curl -sk 'https://lab-confluence.internal:8090/s/x/_/..%2f..%2f..%2fconfluence.cfg.xml' -o /tmp/cve_2026_21589_test.out -w '%{http_code}\n'Cleanup
rm -f /tmp/cve_2026_21589_test.outExpected Telemetry
Web/reverse-proxy access log entry for the lab host showing a request containing '..%2f' sequences and 'confluence.cfg.xml'.
Expected Detection
The kql and spl rules fire on the traversal pattern against an Atlassian endpoint.
Attempts to retrieve a WEB-INF protected resource from a lab Jira instance using directory traversal.
Command
curl -sk 'https://lab-jira.internal:8080/jira/rest/..%252f..%252fWEB-INF%252fweb.xml' -w '%{http_code}\n'Cleanup
echo 'no artifacts to clean'Expected Telemetry
Access log entry with double-encoded '%252f' traversal targeting a /jira/rest/ path and WEB-INF.
Expected Detection
Detection matches the double-encoded (..%252f) and WEB-INF indicators.
Issues a traversal request for a sensitive Unix file path against a lab Atlassian endpoint from a Windows test host to generate detection telemetry.
Command
powershell -c "try { Invoke-WebRequest -Uri 'https://lab-bamboo.internal/bamboo/rest/..%2f..%2f..%2f..%2fetc%2fpasswd' -SkipCertificateCheck -UseBasicParsing } catch { $_.Exception.Response.StatusCode.value__ }"Cleanup
powershell -c "Remove-Variable -Name response -ErrorAction SilentlyContinue"Expected Telemetry
W3CIISLog / reverse-proxy entry showing '..%2f' traversal toward '/etc/passwd' on a /bamboo/ path.
Expected Detection
The kql W3CIISLog rule and QRadar/Chronicle rules match the traversal-to-sensitive-file pattern.