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Compliant Solution (Heartbleed)

OpenSSL version 1.0.1g contains the following patch, which guarantees that payload is within a valid range. The range is limited by the size of the input record.

Code Block
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langc
int dtls1_process_heartbeat(SSL *s) {         
  unsigned char *p = &s->s3->rrec.data[0], *pl;
  unsigned short hbtype;
  unsigned int payload;
  unsigned int padding = 16; /* Use minimum padding */
 
  /* ... More code ... */
 
  /* Read type and payload length first */
  if (1 + 2 + 16 > s->s3->rrec.length)
    return 0; /* Silently discard */
  hbtype = *p++;
  n2s(p, payload);
  if (1 + 2 + payload + 16 > s->s3->rrec.length)
    return 0; /* Silently discard per RFC 6520 */
  pl = p;
 
  /* ... More code ... */
 
  if (hbtype == TLS1_HB_REQUEST) {
    unsigned char *buffer, *bp;
    int r;
 
    /* 
     * Allocate memory for the response; size is 1 byte
     * message type, plus 2 bytes payload length, plus
     * payload, plus padding.
     */
    buffer = OPENSSL_malloc(1 + 2 + payload + padding);
    bp = buffer;
    /* Enter response type, length, and copy payload */
    *bp++ = TLS1_HB_RESPONSE;
    s2n(payload, bp);
    memcpy(bp, pl, payload);
    /* ... More code ... */
  }
  /* ... More code ... */
}

 

Risk Assessment

Depending on the library function called, an attacker may be able to use a heap or stack overflow vulnerability to run arbitrary code.

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