Summary
SimpleChat contains a stored cross-site scripting vulnerability in group document filenames, which are later inserted into inline Share event handlers without safely preserving JavaScript string boundaries. An authenticated group Owner, Admin, or DocumentManager may store script that executes when another group member clicks Share, potentially exposing data and actions available through the victim's session.
SimpleChat contains a stored cross-site scripting vulnerability in group document filenames, which are later inserted into inline Share event handlers without safely preserving JavaScript string boundaries. An authenticated group Owner, Admin, or DocumentManager may store script that executes when another group member clicks Share, potentially exposing data and actions available through the victim's session.
Affected context
The issue occurs in group workspace document handling when:
- An uploaded document filename is controlled by an authenticated group management role
- The filename is persisted and later rendered by
group_workspaces.html - The rendered value is interpolated into an inline Share event handler
- Escaping does not remain safe through HTML decoding and subsequent JavaScript evaluation
Exploitation generally requires another group member to interact with the affected Share control.
The issue occurs in group workspace document handling when:
- An uploaded document filename is controlled by an authenticated group management role
- The filename is persisted and later rendered by
group_workspaces.html - The rendered value is interpolated into an inline Share event handler
- Escaping does not remain safe through HTML decoding and subsequent JavaScript evaluation
Exploitation generally requires another group member to interact with the affected Share control.
Exploit preconditions
- Attack surface: Group document upload and group workspace rendering
- Required access: Authenticated membership with Owner, Admin, or DocumentManager privileges
- Trigger point: A group member clicks the Share control containing the stored filename
- Why exploitation is possible: Attacker-controlled filename data can terminate the inline handler's JavaScript string after the applied escaping is interpreted by the browser
- Attack surface: Group document upload and group workspace rendering
- Required access: Authenticated membership with Owner, Admin, or DocumentManager privileges
- Trigger point: A group member clicks the Share control containing the stored filename
- Why exploitation is possible: Attacker-controlled filename data can terminate the inline handler's JavaScript string after the applied escaping is interpreted by the browser
Why this happens
The underlying bug is a context-confusion error in output encoding. A document filename is treated as data but is inserted into an inline JavaScript handler, where HTML escaping alone does not provide safe JavaScript-string encoding; browser entity decoding can restore characters before script evaluation. This behavior maps to CWE-79: Improper Neutralization of Input During Web Page Generation, specifically stored cross-site scripting caused by placing persistent attacker-controlled data into an executable client-side context.
The underlying bug is a context-confusion error in output encoding. A document filename is treated as data but is inserted into an inline JavaScript handler, where HTML escaping alone does not provide safe JavaScript-string encoding; browser entity decoding can restore characters before script evaluation. This behavior maps to CWE-79: Improper Neutralization of Input During Web Page Generation, specifically stored cross-site scripting caused by placing persistent attacker-controlled data into an executable client-side context.
Potential impact
- Script execution in the SimpleChat origin
- Access to data visible to the victim within the application
- Actions performed with the victim's session and permissions
- Modification of group content or application state
- Exposure of sensitive workspace information
- Abuse of trusted group-member interactions
- Script execution in the SimpleChat origin
- Access to data visible to the victim within the application
- Actions performed with the victim's session and permissions
- Modification of group content or application state
- Exposure of sensitive workspace information
- Abuse of trusted group-member interactions
General mitigation guidance
Mitigation should focus on preventing user-controlled values from entering executable inline JavaScript contexts.
Common defensive patterns include:
- Using framework event binding or trusted DOM APIs instead of inline event handlers
- Keeping document filenames as data attributes or structured values, then treating them as data in client-side code
- Applying context-specific JavaScript-string encoding when a value must cross a JavaScript boundary
- Preferably using safe DOM text and property assignment rather than HTML interpolation
- Enforcing a restrictive Content Security Policy that limits inline script execution
- Validating filenames with an allowlist for business requirements without relying on validation as the primary XSS defense
- Limiting group-management permissions and protecting sensitive actions with server-side authorization checks
Mitigation should focus on preventing user-controlled values from entering executable inline JavaScript contexts.
Common defensive patterns include:
- Using framework event binding or trusted DOM APIs instead of inline event handlers
- Keeping document filenames as data attributes or structured values, then treating them as data in client-side code
- Applying context-specific JavaScript-string encoding when a value must cross a JavaScript boundary
- Preferably using safe DOM text and property assignment rather than HTML interpolation
- Enforcing a restrictive Content Security Policy that limits inline script execution
- Validating filenames with an allowlist for business requirements without relying on validation as the primary XSS defense
- Limiting group-management permissions and protecting sensitive actions with server-side authorization checks
How teams detect issues like this
Detection can combine:
- Static analysis rules for user-controlled values interpolated into inline event handlers
- Code review checks for template output embedded in JavaScript, HTML attributes, or other executable contexts
- Tests using filenames containing quotes, entity-like sequences, and delimiter characters across rendering paths
- Dynamic application testing that verifies stored filenames remain inert when rendered and interacted with
- Content Security Policy reporting to identify unexpected inline script execution
- Repository policy checks that prohibit inline handlers and require context-aware output encoding
Automated code review and security scanning tools may help identify dangerous data-flow paths, but findings should be validated against the browser's parsing and decoding behavior.
Detection can combine:
- Static analysis rules for user-controlled values interpolated into inline event handlers
- Code review checks for template output embedded in JavaScript, HTML attributes, or other executable contexts
- Tests using filenames containing quotes, entity-like sequences, and delimiter characters across rendering paths
- Dynamic application testing that verifies stored filenames remain inert when rendered and interacted with
- Content Security Policy reporting to identify unexpected inline script execution
- Repository policy checks that prohibit inline handlers and require context-aware output encoding
Automated code review and security scanning tools may help identify dangerous data-flow paths, but findings should be validated against the browser's parsing and decoding behavior.
