CVE-2026-67990 Basecamp CVE debrief

Who should care

Defenders responsible for Alertmanager and Prometheus proxy controllers, as well as security teams assessing exposure and potential impact, should prioritize verifying exposure of these controllers in their environment and assess the potential impact of an unauthenticated attacker inducing a logged-in user's browser to submit requests to enabled upstream write or management endpoints.

Why it matters

Unauthenticated attackers can induce logged-in users' browsers to submit requests to enabled upstream write or management endpoints, potentially creating an Alertmanager silence or requesting a Prometheus reload.

• Assess exposure of Alertmanager and Prometheus proxy controllers
• Verify potential impact of unauthenticated requests to enabled upstream services
• Implement measures to prevent or detect unauthorized requests

Technical summary

The basecamp/upright at commit efe4f2e5254ac6e57e45d2261804cca74dbbca3f disables Rails CSRF protection for its Alertmanager and Prometheus proxy controllers, allowing an unauthenticated attacker to induce a logged-in user's browser to submit requests that are forwarded to enabled upstream write or management endpoints. This vulnerability affects the Alertmanager and Prometheus proxy controllers, and its impact depends on the APIs enabled by the upstream services and the exposure of these controllers in the environment.

Defensive priority

Defenders should prioritize verifying exposure of Alertmanager and Prometheus proxy controllers in their environment and assess the potential impact of an unauthenticated attacker inducing a logged-in user's browser to submit requests to enabled upstream write or management endpoints.

Recommended defensive actions

• Verify exposure of Alertmanager and Prometheus proxy controllers in the environment
• Assess the potential impact of an unauthenticated attacker inducing a logged-in user's browser to submit requests to enabled upstream write or management endpoints
• Implement measures to prevent or detect unauthorized requests to upstream services
• Review compensating controls for exposed systems while remediation is scheduled and verified
• Check relevant monitoring, detection, and logs for exposed assets that need extra review
• Track exceptions, retest remediated assets, and close the item only after evidence is documented
• Confirm whether affected product deployments exist in managed environments and assign an owner for follow-up

Evidence notes

The CVE record and NVD vulnerability detail page provide information on the vulnerability, including its description, CVSS score, and references. The basecamp/upright at commit efe4f2e5254ac6e57e45d2261804cca74dbbca3f disables Rails CSRF protection for its Alertmanager and Prometheus proxy controllers. The vulnerability allows an unauthenticated attacker to induce a logged-in user's browser to submit requests that are forwarded to enabled upstream write or management endpoints.

Sources and references

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.