CVE-2026-21582: 
Atlassian Crowd vulnerability analysis and mitigation

CVE-2026-21582 is a Broken Authentication & Session Management (BASM) vulnerability in Atlassian Crowd Data Center that allows an unauthenticated attacker to perform actions as another user. The vulnerability was introduced in version 7.2.1 of Crowd Data Center and was disclosed on August 18, 2026. It also affects Jira Data Center, Jira Service Management Data Center, and other Atlassian products sharing the same component. It carries a CVSS v4.0 base score of 8.8 (High) (Atlassian Advisory, GitHub Advisory).

The vulnerability is classified as Broken Authentication & Session Management (BASM), with no specific CWE assigned in available advisories. The attack vector is network-based, requiring no privileges but involving passive user interaction and specific attack requirements (AT:P), indicating the exploit may depend on particular deployment or execution conditions. An unauthenticated attacker can leverage flawed authentication or session handling logic to impersonate legitimate users and perform actions on their behalf. The vulnerability was discovered and reported through Atlassian's internal Penetration Testing program (Atlassian Advisory, GitHub Advisory).

Successful exploitation allows an unauthenticated attacker to impersonate any user within the Crowd Data Center environment, resulting in high confidentiality and integrity impact on both the vulnerable and subsequent systems. An attacker could access sensitive user data, modify configurations, or perform administrative actions without valid credentials. Availability is not directly impacted, but the ability to act as arbitrary users could facilitate lateral movement across integrated Atlassian products that rely on Crowd for centralized authentication (Atlassian Advisory, GitHub Advisory).

As of the disclosure date (August 18, 2026), there is no public proof-of-concept exploit and no evidence of active in-the-wild exploitation. The EPSS score is 0.0, reflecting a currently low probability of exploitation in the near term. The vulnerability has not been added to the CISA Known Exploited Vulnerabilities (KEV) catalog. No threat actor attribution has been reported (GitHub Advisory).

Atlassian recommends upgrading Crowd Data Center to version 7.2.2 or later; versions 7.2.2 to 7.2.3 are confirmed unaffected. The same CVE identifier also applies to Jira Data Center and Jira Service Management Data Center, which should be upgraded to their respective fixed versions as listed in the August 18, 2026 Security Bulletin. If immediate upgrade is not possible, administrators should monitor authentication logs for unauthorized user actions and restrict network access to Crowd instances. No specific configuration-based workaround has been published by Atlassian (Atlassian Advisory, GitHub Advisory).

The vulnerability was disclosed as part of Atlassian's August 18, 2026 monthly Security Bulletin, which covered 162 high-severity and 10 critical-severity vulnerabilities across multiple products. No notable independent researcher commentary or significant social media discussion has been identified beyond standard vulnerability aggregator coverage at the time of disclosure.