Java SSRF Findings

Inizia con gli snippet di Java Controller e Service Layer, tracciando l’input dalla variabile di percorso, attraverso la costruzione dell’URI, fino al sink RestTemplate.exchange(). Verifica come l’analisi SSRF pertinente di CodeQL gestisce gli URL di base inclusi nell’allowlist e la validazione dell’URI; il lavoro è completato quando si determina se si tratta di un falso positivo riproducibile della query oppure si identificano le evidenze mancanti necessarie per il triage.

Hi Team,

Hope you're doing well!

Just adding this here as a question to check if anyone has any inputs or recommendations.

Description of issue

CWE-918 (SSRF) finding alert when input parameters are eventually appended to a URL used to make outbound calls to external systems in the source code.

However, the implementation includes multiple layers of mitigation, which I believe should prevent SSRF:

• The input string is validated via regex (alphanumeric + length check).
• A sanitization method strips any non-alphanumeric characters.-
• The base URL is sourced from a secure Spring Boot config (application.properties) using the @Value annotation.
• I’ve implemented an allow-list validation, ensuring the final URI starts with one of the expected base URLs.
• Despite these controls, CodeQL still flags the usage as SSRF in the RestTemplate.exchange() call.

Please refer to the code snippet below for reference:

Code samples or links to source code

Controller(source)

@RequestMapping(path = "{inputKey:^[a-zA-Z0-9]{8}$|^[a-zA-Z0-9]{10}$}", method = RequestMethod.GET, produces = MediaType.APPLICATION_JSON_VALUE)
@ApiResponses({ @ApiResponse(responseCode = "404", description = "Resource Not Found"),
       @ApiResponse(responseCode = "200", description = "OK") })
public ResourceResponse getURLsByIdentifier(
       @Parameter(description = "Enter inputKey.", name = "inputKey", required = true) @PathVariable("inputKey") String inputKey) {

    ###    Source inputKey
    return resourceService.getResourceUrls(sanitizeAlphanumeric(inputKey));
}

private String sanitizeAlphanumeric(String input) {
    if (input == null) return "";
    return input.replaceAll("[^a-zA-Z0-9]", "");
}

Service Layer (Sink)

//validated URL is being formed
URI configURI = UriComponentsBuilder.
        fromUriString(baseUrl) //baseURl is pickup from Spring config using @Value annotation
        .path(inputKey) // pased from controller
        .queryParam("config", "true")
        .build()
        .toUri();
		
HttpEntity<String> entity = new HttpEntity<>(getHeaders());

### Sink configURI
ResponseEntity<Map<String, Object>> response = restTemplate.exchange(configURI, HttpMethod.GET, entity,
        new ParameterizedTypeReference<>() {}); // Vunerbility reported here 

//have implemented a URL validation mechanism by maintaining a map of all allowed base URLs and verifying 
// whether the constructed configURI starts with one of the expected base URLs. However, this approach also did not help resolve the issue.

I’ve also verified that:

baseUrl is always from a known set of safe endpoints.
A custom check ensures the final URI starts with one of the allow-listed base URLs before making the request.

Appreciate any insights or suggestions. Happy to share more details if needed. Thanks in advance!