The bug is a classic time‑of‑check to time‑of‑use race condition in the Webhook/Notification validate_restricted_url function of Prefect. An attacker can supply a malicious URL that passes the initial restriction check, but before the URL is resolved the environment can be modified, causing the URL to point to an unintended location. This flaw is classified as CWE‑362 and CWE‑367 and allows a remote attacker to bypass the intended restriction on webhook destinations, potentially leading to unintended networking or data exfiltration, but it does not provide arbitrary code execution or system compromise.

PrefectHQ Prefect versions up to and including 3.6.28.dev1 are affected. These snapshots are identified by the CPE of cpe:2.3:a:prefect:prefect:*:*:*:*:*:*:*:* and are used by deployments that have not yet applied the fix commit 7c70ac54a5e101431d83b9f2681ec88d5e0021ed. From 3.6.28.dev2 and later the issue is resolved.

The CVSS score of 2.3 reflects a low overall severity, and the EPSS score of <1% indicates limited exploitation pressure. The vulnerability is not listed in CISA’s KEV catalog. An attacker would need to reliably trigger a race condition from a remote target, a task described as high‑complexity and difficult to execute in practice. Consequently the likelihood of real‑world attacks is currently low, but it should still be remedied to eliminate the possibility of a URL restriction bypass.