CVE-2026-27197 is a critical vulnerability classified under CWE-287 (Improper Authentication) affecting the SAML Single Sign-On (SSO) implementation in Sentry, a widely used developer error tracking and performance monitoring tool. The flaw exists in versions 21.12.0 through 26.1.0 and allows an attacker to impersonate any user account by exploiting the trust relationship between Sentry and a malicious SAML Identity Provider (IdP). Specifically, in multi-organization Sentry instances, an attacker controlling a malicious IdP for one organization can manipulate authentication flows to gain access to accounts in another organization hosted on the same instance. For self-hosted deployments, the risk applies only if multiple organizations are configured (SENTRY_SINGLE_ORGANIZATION set to True) or if an attacker already has permissions to modify SSO settings for other organizations. The vulnerability requires no prior privileges or user interaction, making it highly exploitable remotely. The impact includes full compromise of user accounts, leading to unauthorized access to sensitive error logs, performance data, and potentially further lateral movement within the affected environment. The vendor addressed this issue in version 26.2.0. As a temporary mitigation, enabling user account-based two-factor authentication (2FA) can prevent attackers from completing authentication even if they exploit the SAML flaw. However, 2FA must be enabled by individual users, as organization administrators cannot enforce it on their behalf. No known exploits are currently reported in the wild, but the critical nature and ease of exploitation warrant immediate attention.

The vulnerability poses a severe risk to organizations using Sentry, especially those with multi-organization instances or self-hosted deployments configured for multiple organizations. Successful exploitation allows attackers to fully compromise user accounts without needing credentials or user interaction, threatening confidentiality and integrity of sensitive application error data and performance metrics. This can lead to unauthorized disclosure of proprietary or personal information, manipulation or deletion of error tracking data, and potential pivoting to other internal systems. The lack of required privileges and user interaction significantly increases the attack surface and likelihood of exploitation. Organizations relying on Sentry for monitoring critical applications may face operational disruptions, data breaches, and loss of trust from customers and stakeholders. The vulnerability's critical severity (CVSS 9.1) reflects its potential to cause widespread damage if left unpatched.

1. Immediately upgrade all affected Sentry instances to version 26.2.0 or later, where the vulnerability is fixed. 2. For self-hosted environments, review and adjust the SENTRY_SINGLE_ORGANIZATION setting to limit multi-organization configurations where feasible. 3. Enforce user account-based two-factor authentication (2FA) across all user accounts to add an additional layer of security; educate users on enabling 2FA since administrators cannot enforce it on their behalf. 4. Audit and restrict permissions related to SSO settings modification to trusted personnel only, minimizing risk of malicious configuration changes. 5. Monitor authentication logs for unusual SAML IdP activities or login attempts from unrecognized providers. 6. Consider isolating organizations on separate Sentry instances to reduce cross-organization attack vectors. 7. Regularly review and update SAML IdP configurations to ensure only trusted providers are authorized. 8. Implement network segmentation and access controls to limit exposure of Sentry management interfaces. 9. Stay informed on any emerging exploits or patches related to this vulnerability.