CVERadar
CRITICAL · CVSS 4.0 9.3CISA KEV · added 2026-10-15Public PoCEPSS 12.71% (p96)Threat level 65

CVE-2026-21589: Atlassian Multiple Products Files or Directories Accessible to External Parties Vulnerability

Atlassian · Multiple Products · NVD published 2026-10-06 · posted 2026-10-21 · last modified 2026-10-20

What it is

This is a vulnerability in Bitbucket Data Center, Confluence Data Center, Jira Service Management Data Center, Jira Software Data Center, Bamboo Data Center. Crowd Data Center, Crucible and Fisheye. This Arbitrary File Access vulnerability allows an unauthenticated attacker to access specific files within the web application root directory in affected versions. Exploitation requires prior knowledge of the target file's exact name and path; this vulnerability does not allow attackers to enumerate or list directory contents. In some configurations, there may be some sensitive files that make this highly severe. This vulnerability allows an unauthenticated remote attacker to access specific files within the web application root directory in affected versions. The vulnerability must be addressed for affected versions of: -- Bitbucket Data Center, introduced in version >= 4.6.0, fix versions: 9.4.26, 10.2.8, 10.5.1 -- Confluence Data Center, introduced in version >= 5.10.0, fix versions 9.2.26, 10.2.19 -- Crowd Data Center, introduced in version >= 2.11.0, fix versions 6.3.7, 7.0.3, 7.1.7, 7.2.4 -- Jira Software Data Center, introduced in version >= 7.1.0, fix versions 9.12.40, 10.3.26, 11.3.12 -- Jira Service Management Data Center, introduced in version >= 3.1.0, fix versions 5.12.40, 10.3.26, 11.3.12 -- Bamboo Data Center >= 7.0.1, fix versions 10.2.24, 12.1.12 -- Crucible, fix versions 4.9.15 -- Fisheye, fix version 4.9.15 -- Exploitation requires prior knowledge of the target file's exact name and path. The vulnerability does not include the capability to enumerate or list directory contents.

WeaknessCWE-552
CVSS vectorCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:N/VA:N/SC:H/SI:H/SA:H/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X (source: [email protected])
CISA due date2026-10-18 (for US federal agencies under BOD; a good deadline for everyone)
ATT&CK tacticsInitial Access

Step-by-step fix guide: How to fix CVE-2026-21589: Atlassian Multiple Products (exploited in the wild)

Exploitation evidence

First exploit evidence seen: 2026-10-06 (earliest date across the sources below).

Exploited in the wild

  • CISA KEV: listed since 2026-10-15. Source

Public exploit code

GitHub proof-of-concept repositories

13 public repositories from 13 accounts, first seen 2026-10-06. Most starred: watchtowrlabs/watchTowr-vs-Atlassian-CVE-2026-21589 (15 stars), view repository.

Verify before running: public PoCs can be malicious. Read the code and only run it in an isolated lab. A PoC means exploit code is public, not that this CVE is exploited in the wild.

Sources: CISA KEV · nomi-sec/PoC-in-GitHub.

Defend the Chain

The attack chain for CVE-2026-21589 laid across the MITRE ATT&CK Enterprise tactics. Solid cards come from the MITRE CTID KEV mappings; dashed cards are inferred by CVERadar from the CWE or description. Correct defences are real ATT&CK mitigations for that technique.

Threat level 65/100
Defender level 1 · 0 XP
Chain links broken: 0/1

Reconnaissance

Resource Development

Initial Access

Execution

Persistence

Privilege Escalation

Stealth

Defense Impairment

Credential Access

Discovery

Lateral Movement

Collection

Command and Control

Exfiltration

Impact

Pick a red technique card on the board, then choose the defence that stops it.

Defend against T1190 Exploit Public-Facing Application Inferred

Inferred from description keywords (network-reachable flaw)

How to fix it

CISA required action

Apply mitigations in accordance with vendor instructions, ensuring compliance with CISA’s BOD 26-04 Prioritizing Security Updates Based on Risk (see URL in Notes) guidance and CISA’s “Forensics Triage Requirements” (see URL in Notes). Follow applicable BOD 26-04 guidance for cloud services or discontinue use of the product if mitigations are unavailable. Stakeholders are responsible for evaluating each asset's internet exposure and ensuring adherence to BOD 26-04 patching guidelines. (source: CISA KEV)

Fixed versions

  • atlassian bitbucket data center: upgrade to 9.4.26 or later (affected from 7.17.0)
  • atlassian bitbucket data center: upgrade to 10.2.8 or later (affected from 9.5.0)
  • atlassian bitbucket data center: upgrade to 10.5.1 or later (affected from 10.3.0)
  • atlassian confluence data center: upgrade to 9.2.26 or later (affected from 5.10.0)
  • atlassian confluence data center: upgrade to 10.2.19 or later (affected from 9.3.0)
  • atlassian crowd: upgrade to 6.3.7 or later (affected from 2.11.0)
  • atlassian crowd: upgrade to 7.0.3 or later (affected from 7.0.0)
  • atlassian crowd: upgrade to 7.1.7 or later (affected from 7.1.0)
  • atlassian crowd: upgrade to 7.2.4 or later (affected from 7.2.0)
  • atlassian jira data center: upgrade to 9.12.40 or later (affected from 7.1.0)
  • atlassian jira data center: upgrade to 10.3.26 or later (affected from 9.13.0)
  • atlassian jira data center: upgrade to 11.3.12 or later (affected from 10.4.0)
  • atlassian jira service management: upgrade to 5.12.40 or later (affected from 4.14.0)
  • atlassian jira service management: upgrade to 10.3.26 or later (affected from 5.13.0)
  • atlassian jira service management: upgrade to 11.3.12 or later (affected from 10.4.0)
  • atlassian bamboo: upgrade to 10.2.24 or later (affected from 7.0.1)
  • atlassian bamboo: upgrade to 12.1.12 or later (affected from 11.0.0)
  • atlassian crucible: upgrade to 4.9.15 or later
  • atlassian fisheye: upgrade to 4.9.15 or later

Derived from the NVD CPE configuration (versionEndExcluding / versionEndIncluding). Always confirm with the vendor advisory.

Vendor advisories and patches

MITRE ATT&CK mitigations for this chain

  • M1048 Application Isolation and Sandboxing (for T1190) : Application isolation will limit what other processes and system features the exploited target can access.
  • M1037 Filter Network Traffic (for T1190) : Restrict outbound network traffic from public-facing servers to prevent unauthorized connections from initiating communications with attacker-controlled infrastructure. While this may not prevent the initial exploitation, it limits the attacker's ability to verify and control the compromised server post-exploit, reduci
  • M1030 Network Segmentation (for T1190) : Segment externally facing servers and services from the rest of the network with a DMZ or on separate hosting infrastructure.
  • M1016 Vulnerability Scanning (for T1190) : Regularly scan externally facing systems for vulnerabilities and establish procedures to rapidly patch systems when critical vulnerabilities are discovered through scanning and through public disclosure.
  • M1026 Privileged Account Management (for T1190) : Use least privilege for service accounts will limit what permissions the exploited process gets on the rest of the system.
  • M1050 Exploit Protection (for T1190) : Web Application Firewalls may be used to limit exposure of applications to prevent exploit traffic from reaching the application.
  • M1035 Limit Access to Resource Over Network (for T1190) : Ensure that all publicly exposed services are actually intended to be so, and restrict access to any that should only be available internally.
  • M1051 Update Software (for T1190) : Update software regularly by employing patch management for externally exposed applications.

Detection Generic guidance

  • Initial Access: Alert on unusual requests to the affected service (odd paths, oversized payloads, exploit strings) in WAF, reverse-proxy and application logs.

Response checklist Generic guidance

  1. Inventory: find every instance of the affected product and version (include internet-facing and forgotten ones).
  2. Patch or mitigate per the vendor advisory; if you cannot patch, remove internet exposure or apply the vendor workaround.
  3. Assume compromise if the system was exposed before patching: hunt for the indicators in the advisory and review logs back to the disclosure date.
  4. Rotate credentials and secrets stored on or used by the affected system if compromise cannot be ruled out.

Sources