Coder allows organizations to provision remote development environments via Terraform. The vulnerability occurs when the coder open app command opens an external workspace‑app URL without validating its scheme or host. When that URL contains the $SESSION_TOKEN placeholder, the CLI substitutes it with the user’s real session token before handing the URL to the operating‑system open handler. This can expose the session token to an arbitrary host or scheme, enabling an attacker who controls a malicious template author to gain authenticated access. The flaw is a sensitive information exposure and an open‑redirect, classified as CWE‑522 and CWE‑601.

The flaw existed in coder releases older than 2.29.7, 2.32.7, 2.33.8, and 2.34.2. Organizations running any earlier version of coder are vulnerable when they use coder open app on workspaces that contain external app URLs controlled by a template author and containing the $SESSION_TOKEN placeholder. The issue is limited to the command‑line tool; the web interface is unaffected.

The CVSS base score of 7.7 and EPSS score less than 1% indicate a high‑severity but low exploitation probability. The flaw is not listed in the CISA KEV catalog. Exploitation requires the user to run coder open app on a workspace with an attacker‑controlled external‑app definition, so the attack vector is local command execution. The compromised token can be reused against trusted Coder instances, allowing the attacker to impersonate the victim or read sensitive workspace data. Because the defect involves an unvalidated URL scheme, the risk is mitigated by restricting open actions to trusted protocols.