Coder vulnerable to privilege escalation could lead to a cross workspace compromise

## Summary Insecure session handling opened room for a privilege escalation scenario in which [prebuilt workspaces](https://coder.com/docs/admin/templates/extending-templates/prebuilt-workspaces) could be compromised by abusing a shared system identity. ## Details Coder automatically generates a session token for a user when a workspace is started. It is automatically exposed via [`coder_workspace_owner.session_token`](https://registry.terraform.io/providers/coder/coder/latest/docs/data-sources/workspace_owner#session_token-1). Prebuilt workspaces are initially owned by a built-in `prebuilds` system user. When a prebuilt workspace is claimed, a new session token is generated for the user that claimed the workspace, but the previous session token for the `prebuilds` user was not expired. Any Coder workspace templates that persist this automatically generated session token are potentially impacted. For example, the [coder-login module](https://github.com/coder/registry/blob/8677e7d52b374b025c4820d09049dc6b008beee8/registry/coder/modules/coder-login/run.sh) allows template authors to automatically configure the coder CLI to be authenticated with the Coder deployment. This causes a script to be run on workspace startup that runs the command `coder login` using the automatically generated user session token c.f. [https://github.com/coder/registry/blob/8677e7d52b374b025c4820d09049dc6b008beee8/registry/coder/modules/coder-login/main.tf#L23](https://github.com/coder/registry/blob/8677e7d52b374b025c4820d09049dc6b008beee8/registry/coder/modules/coder-login/main.tf#L23) This module was originally written before the inception of the [prebuilds](https://coder.com/docs/admin/templates/extending-templates/prebuilt-workspaces) feature in Coder, which essentially creates a "pre-warmed" pool of workspaces owned by a particular `prebuilds` system user. When this module is invoked on a prebuilt workspace, it causes the Coder CLI inside the workspace to persist the session token for the `prebuilds` user to disk. Because the `coder-login` module checks if the CLI is authenticated, the script exits early before updating the session token, leaving the Coder CLI authenticated as the `prebuilds`user upon claim: ## Impact > Important: **Deployments that have never utilized the [prebuilds](https://coder.com/docs/admin/templates/extending-templates/prebuilt-workspaces) feature are not affected by this vulnerability.** This vulnerability requires a previously authenticated user to claim a prebuilt workspace from a template configured to store the prebuilds user session token as described above. The `prebuilds` user has no specific roles, so its credential has the same level of access as a regular member user, meaning a user with the `prebuilds` user's credential can move laterally to any other prebuilt workspace, or create new workspaces as the `prebuilds` user. This means that a malicious authenticated actor can potentially execute code on other workspaces owned by the `prebuilds` user and potentially access information of other users once they claim a previously poisoned workspace. ## Remediation Fixed in https://github.com/coder/coder/pull/19667 Note that prebuilt workspaces claimed previous to the fix may have been affected by this vulnerability. It is recommended that users re-create their workspace if it was created from a prebuild. To identify potentially affected workspaces, run the following SQL query against the Coder database: ```sql SELECT w.id, w.name, w.owner_id, u.email FROM workspaces w LEFT JOIN users u ON u.id = w.owner_id WHERE w.owner_id <> 'c42fdf75-3097-471c-8c33-fb52454d81c0'::uuid AND NOT w.deleted AND EXISTS ( SELECT 1 FROM workspace_builds AS wb WHERE wb.workspace_id = w.id AND wb.initiator_id = 'c42fdf75-3097-471c-8c33-fb52454d81c0'::uuid ); ``` > Previous manually created tokens for the prebuilds user are left as-is. You may wish to review these via `coder tokens list --all` --- [Premium license](https://coder.com/docs/admin/licensing) customers can also take advantage of the [audit logs](https://coder.com/docs/admin/security/audit-logs) feature to query actions performed by the `prebuilds` user. Following [filter](https://coder.com/docs/admin/security/audit-logs#how-to-filter-audit-logs) can be used to verify if no [API keys](https://coder.com/docs/reference/api/users#create-token-api-key) were created by the `prebuilds` user > would indicate a potentially malicious action aimed at achieving [persistence](https://attack.mitre.org/tactics/TA0003/) ``` username:prebuilds resource_type:api_key ``` Following [filter](https://coder.com/docs/admin/security/audit-logs#how-to-filter-audit-logs) can be used to list all *write* operations performed by the `prebuilds` user (including failed attempts to update various settings) ``` username:prebuilds action:write ``` ### Patched versions - [2.24.4](https://github.com/coder/coder/releases/tag/v2.24.4) - [2.25.2](https://github.com/coder/coder/releases/tag/v2.25.2) - [2.26.0](https://github.com/coder/coder/releases/tag/v2.26.0)

Source published

5 Sep 2025 20:19:58 UTC

Source modified

17 Sep 2025 17:42:08 UTC

Observed here

24 Oct 2026 13:19:41 UTC

Source terms

GitHub Advisory Database · CC-BY-4.0

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: osv · GitHub Advisory Database · CC-BY-4.0. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS_V3 · CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N

Publisher rating · HIGH