Summary
Backstage Bitbucket pull-request Scaffolder actions may insufficiently validate filesystem paths, allowing an authenticated user to influence locations outside the intended working area. If the user can run an eligible template and control an allowed Bitbucket repository, the issue could expose or alter backend files and affect service availability.
Backstage Bitbucket pull-request Scaffolder actions may insufficiently validate filesystem paths, allowing an authenticated user to influence locations outside the intended working area. If the user can run an eligible template and control an allowed Bitbucket repository, the issue could expose or alter backend files and affect service availability.
Affected context
The vulnerability can occur in Backstage deployments that use the Bitbucket Cloud or Bitbucket Server Scaffolder backend modules for pull-request actions. Risk depends on whether authenticated users can execute eligible templates and influence repository content or parameters that reach filesystem operations without sufficiently constrained path validation.
The vulnerability can occur in Backstage deployments that use the Bitbucket Cloud or Bitbucket Server Scaffolder backend modules for pull-request actions. Risk depends on whether authenticated users can execute eligible templates and influence repository content or parameters that reach filesystem operations without sufficiently constrained path validation.
Exploit preconditions
- Attack surface: Backstage Scaffolder Bitbucket pull-request actions
- Required access: Authenticated access sufficient to execute an eligible template
- Required influence: Ability to influence an allowed Bitbucket repository or related input
- Trigger point: Filesystem operations performed while processing the pull-request action
- Why exploitation is possible: User-controlled path information may resolve outside the intended working directory, potentially including paths affected by symbolic-link behavior
- Attack surface: Backstage Scaffolder Bitbucket pull-request actions
- Required access: Authenticated access sufficient to execute an eligible template
- Required influence: Ability to influence an allowed Bitbucket repository or related input
- Trigger point: Filesystem operations performed while processing the pull-request action
- Why exploitation is possible: User-controlled path information may resolve outside the intended working directory, potentially including paths affected by symbolic-link behavior
Why this happens
The underlying bug is insufficient restriction and canonicalization of filesystem paths derived from user-influenced repository or template data. When an application accepts a path without reliably constraining its resolved location to an approved working area, path traversal can reach unintended filesystem objects. This maps primarily to CWE-22, Improper Limitation of a Pathname to a Restricted Directory, with CWE-59 relevant where symbolic links can redirect operations outside the expected path boundary.
The underlying bug is insufficient restriction and canonicalization of filesystem paths derived from user-influenced repository or template data. When an application accepts a path without reliably constraining its resolved location to an approved working area, path traversal can reach unintended filesystem objects. This maps primarily to CWE-22, Improper Limitation of a Pathname to a Restricted Directory, with CWE-59 relevant where symbolic links can redirect operations outside the expected path boundary.
Potential impact
- An attacker may read sensitive backend files
- An attacker could modify or delete files accessible to the backend process
- Backend configuration or source material may be exposed or altered
- Service availability could be degraded
- Compromise may extend to other resources reachable through the backend's privileges
- An attacker may read sensitive backend files
- An attacker could modify or delete files accessible to the backend process
- Backend configuration or source material may be exposed or altered
- Service availability could be degraded
- Compromise may extend to other resources reachable through the backend's privileges
General mitigation guidance
Mitigation generally focuses on enforcing a strict filesystem trust boundary
around every path used by Scaffolder actions.
Common defensive patterns include:
- Resolve and canonicalize paths before use, then verify they remain beneath an approved directory
- Prefer controlled identifiers over user-supplied filesystem paths
- Reject traversal segments, absolute paths, and unexpected path formats
- Account for symbolic links and race conditions when validating and accessing files
- Use isolated, temporary working directories with restrictive permissions
- Run backend workers with least privilege and limit access to sensitive filesystem locations
- Keep repository content and template inputs untrusted by default
Mitigation generally focuses on enforcing a strict filesystem trust boundary
around every path used by Scaffolder actions.
Common defensive patterns include:
- Resolve and canonicalize paths before use, then verify they remain beneath an approved directory
- Prefer controlled identifiers over user-supplied filesystem paths
- Reject traversal segments, absolute paths, and unexpected path formats
- Account for symbolic links and race conditions when validating and accessing files
- Use isolated, temporary working directories with restrictive permissions
- Run backend workers with least privilege and limit access to sensitive filesystem locations
- Keep repository content and template inputs untrusted by default
How teams detect issues like this
Detection approaches can include:
- Static analysis for path joins, file operations, and archive or repository extraction using user-influenced values
- Code review checks for canonicalization performed after file access or for validation based only on string prefixes
- Tests covering relative paths, absolute paths, encoded traversal, symlinks, and concurrent filesystem changes
- Policy enforcement requiring approved-directory checks before filesystem access
- Runtime monitoring for Scaffolder processes accessing paths outside designated workspaces
- Automated security review tools that flag path traversal and unsafe link-following patterns
Detection approaches can include:
- Static analysis for path joins, file operations, and archive or repository extraction using user-influenced values
- Code review checks for canonicalization performed after file access or for validation based only on string prefixes
- Tests covering relative paths, absolute paths, encoded traversal, symlinks, and concurrent filesystem changes
- Policy enforcement requiring approved-directory checks before filesystem access
- Runtime monitoring for Scaffolder processes accessing paths outside designated workspaces
- Automated security review tools that flag path traversal and unsafe link-following patterns
