The flaw arises because the BlockNote editor extension for OpenProject fails to enforce that the work package identifier is a numeric value. This omission allows an attacker to embed crafted relative links inside a collaborative document. When a user opens such a document, the client side of OpenProject automatically performs arbitrary GET requests to any URL inside the same instance. The resulting behaviour can trigger forced actions, create misleading or spoofed content, and lead to a persistent denial‑of‑service condition. The weakness is a classic example of insecure input validation (CWE‑345). If a user’s browser issues requests to internal endpoints that perform state‑changing operations, the attacker can exercise unintended control over the system without elevated privileges.

The affected deployments are OpenProject 17.0.0 and 17.0.1 that include the pre‑patched op‑blocknote‑extensions. The vulnerability is corrected in OpenProject 17.0.2, which ships with op‑blocknote‑extensions v0.0.22, or later releases.

The CVSS score of 6.3 indicates moderate severity. The EPSS score of less than 1 % suggests a very low probability of exploitation. The vulnerability is not listed in the CISA KEV catalog. The likely attack vector requires a malicious document to be opened by a user, making it a user‑involved or “social‑engineering” style exploit.