CVE-2026-55431 coder vulnerability
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.
Quick answer
coder should be reviewed and updated if it matches the affected versions. The recommended fix is to apply the vendor-supported patched version or the mitigation steps below, then retest the public website with Fixnx.
Who is affected
Affected versions
- Review vendor advisory for affected versions.
Fixed versions
- Apply the latest vendor-supported patched version.
How to fix it
CVE-2026-55431 affects Coder remote development deployments before the patched Coder releases. The practical risk is session token exposure through unsafe external workspace app URLs opened by the Coder CLI. Prioritize environments where template authors can define external app URLs or users run coder open app for untrusted workspaces. Coder fixed this issue in versions 2.29.7, 2.32.7, 2.33.8, and 2.34.2; deploy the matching patched branch or a later supported release. Where the advisory lists a workaround, apply it only as a temporary control until the patched version is deployed.
- Inventory all Coder server, CLI, provisioner, AI Bridge Proxy, workspace app proxy, and template-author deployments across production, staging, and developer environments.
- Identify affected Coder versions and compare each deployment against the fixed releases: 2.29.7, 2.32.7, 2.33.8, and 2.34.2, or a later supported release.
- Upgrade Coder servers and related components to the patched release for the installed branch, then roll out updated CLI binaries to users and automation hosts where the CLI is affected.
- Restrict untrusted templates and tell users not to run coder open app against untrusted workspaces until the CLI is patched.
- Review role bindings, template-author privileges, provisioner daemon access, wildcard app hostname exposure, and reverse proxy header handling for unnecessary trust.
- Review template app definitions, CLI usage, and authentication events for suspicious external URLs or session-token exposure.
- If exploitation or credential exposure is suspected, revoke affected sessions, rotate tokens and credentials, preserve audit logs, and rebuild affected workspaces or hosts where integrity cannot be trusted.
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Verify the fix
- Confirm every Coder component reports a patched version: 2.29.7, 2.32.7, 2.33.8, and 2.34.2, or a later supported release for that branch.
- Confirm the CLI applies URL scheme and trusted-destination checks before substituting $SESSION_TOKEN.
- Validate proxy, wildcard app hostname, template, provisioner, and workspace permission settings against the intended least-privilege policy.
- Review Coder audit logs, reverse proxy logs, and workspace telemetry for exploitation attempts before and after patching.
- Document patched versions, changed settings, residual exceptions, and evidence, then rerun Fixnx or the relevant vulnerability scan where applicable.
Related categories
Trusted references
FAQ
What is affected by CVE-2026-55431?
coder should be checked against the vendor advisory and trusted references linked on this page.
What should I fix first?
Start with internet-facing sites, admin panels, login flows, plugins, themes, modules, packages, and systems that process user-controlled input or sensitive data.
How do I confirm the fix worked?
Apply the patched version or mitigation, clear caches where relevant, retest the affected workflow, and run a new Fixnx scan to verify public website exposure signals.
How are Fixnx security risk categories chosen?
Fixnx keeps one canonical risk page and assigns only broad, relevant categories such as ecosystem, technology area, or vulnerability class.