[MESOS-9411] Validation of JWT tokens using HS256 hashing algorithm is not thread safe.

• Type: Bug
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 1.5.1, 1.6.0, 1.7.0, 1.8.0
• Fix Version/s: 1.5.3, 1.6.2, 1.7.1, 1.8.0
• Component/s: libprocess
• Labels: integration mesosphere security
• Target Version/s: 1.5.1, 1.6.1, 1.7.0, 1.8.0
• Sprint: Mesos Integration R8 Sprint 34
• Story Points: 5
• Assignee: Alexander Rojas
• Reporter: Alexander Rojas
• Shepherd: Till Toenshoff
• Created: 21/Nov/18 13:46
• Updated: 29/Apr/19 09:27
• Resolved: 01/Dec/18 14:36

Description

from the OpenSSL documentation:

It places the result in md (which must have space for the output of the hash function, which is no more than EVP_MAX_MD_SIZE bytes). If md is NULL, the digest is placed in a static array. The size of the output is placed in md_len, unless it is NULL. Note: passing a NULL value for md to use the static array is not thread safe.

We are calling HMAC() as follows:

  unsigned int md_len = 0;

  unsigned char* rc = HMAC(
      EVP_sha256(),
      secret.data(),
      secret.size(),
      reinterpret_cast<const unsigned char*>(message.data()),
      message.size(),
      nullptr,       // <----- This is `md`
      &md_len);

  if (rc == nullptr) {
    return Error(addErrorReason("HMAC failed"));
  }

  return string(reinterpret_cast<char*>(rc), md_len);

Given that this code does not run inside a process, race conditions could occur.