CVE-2026-55431: Coder's session token leaked to arbitrary hosts via `coder open app` for external workspace apps

Severity: medium (CVSS 6.1 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.3% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-07-08 · updated 2026-07-08
Weakness: CWE-522

Description

Coder allows organizations to provision remote development environments via Terraform. Prior to versions 2.29.7, 2.32.7, 2.33.8, and 2.34.2, `coder open app` opens external workspace-app URLs without validating the scheme or host. When an external app URL contains the `$SESSION_TOKEN` placeholder the CLI replaces it with the user's real session token before handing the URL to the OS open handler. Practical exploitation requires the victim to run `coder open app` against a workspace whose external app definition the attacker controls. Only a malicious template author can control external app URLs. The fix in versions 2.29.7, 2.32.7, 2.33.8, and 2.34.2 applies a URL-scheme allowlist in the CLI and limits `$SESSION_TOKEN` substitution to trusted destinations like the web frontend. As a workaround, avoid running `coder open app` for untrusted workspaces.

Affected products

coder: before 2.29.17; from 2.30.0 before 2.32.7; from 2.33.0 before 2.33.8; from 2.34.0 before 2.34.2 — fixed in 2.29.17, 2.32.7, 2.33.8, 2.34.2

How to fix

Upgrade to a fixed version: coder 2.29.17, 2.32.7, 2.33.8, 2.34.2. Check the vendor advisory for mitigations.

References

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