Attack Chain

1. Attacker gains elevated access: The attacker acquires "template authorship" or "external provisioner operator" privileges within the Coder environment, which is a prerequisite for exploitation.
2. Victim app ID discovery: The attacker uses the Coder public API to identify and obtain the unique UUID of a target victim's workspace application.
3. Attacker creates malicious agent: The attacker sets up their own workspace and agent, which will be used to intercept the victim's traffic.
4. Craft CompleteJob payload: The attacker constructs a CompleteJob payload containing the victim's discovered app UUID and their own malicious agent ID.
5. Submit payload: The attacker submits the crafted CompleteJob payload to the Coder system, leveraging their elevated provisioner permissions.
6. Cross-workspace agent rebinding: The UpsertWorkspaceApp function, vulnerable to the ID conflict, overwrites the agent_id associated with the victim's app UUID, reassigning it to the attacker's agent ID.
7. Traffic interception: Subsequent network traffic, including IDE and terminal sessions initiated by the victim for their workspace application, is transparently proxied to the attacker's workspace and agent.
8. Session compromise: The attacker can now monitor, control, and potentially exfiltrate data from the victim's development environment sessions, leading to unauthorized access and data compromise.

Impact

Successful exploitation of CVE-2026-55429 allows an attacker with pre-existing elevated permissions to effectively hijack a victim's Coder workspace sessions. This means all activity within the victim's IDE and terminal, including sensitive data, code, credentials, and commands, can be monitored and manipulated by the attacker. This privilege escalation enables unauthorized access to intellectual property, potential insertion of malicious code, and broader compromise of development pipelines, affecting all users of vulnerable Coder instances across various sectors utilizing the platform for development environments.

Recommendation

• Prioritize patching all Coder instances to versions v2.34.2, v2.33.8, v2.32.7, or v2.29.17 to remediate CVE-2026-55429.
• Regularly review and limit permissions for "template author" and "external provisioner operator" roles to only essential personnel to reduce the attack surface for CVE-2026-55429.