Ransomware

Ransomware is a type of malware that restricts access to the infected computer system in some way, and demands that the user pay a ransom to the malware operators to remove the restriction. Some forms of ransomware systematically encrypt files on the system's hard drive, which become difficult or impossible to decrypt without paying the ransom for the encryption key, while some may simply lock the system and display messages intended to coax the user into paying. Ransomware typically propagates as a trojan, whose payload is disguised as a seemingly legitimate file; thus, ransomware is an access-denial type of attack that prevents legitimate users from accessing files.[1]

While initially popular in Russia, the use of ransomware scams has grown internationally;[2][3][4] in June 2013, security software vendor McAfee released data showing that it had collected over 250,000 unique samples of ransomware in the first quarter of 2013, more than double the number it had obtained in the first quarter of 2012.[5] Wide-ranging attacks involving encryption-based ransomware began to increase through trojans such as CryptoLocker, which had procured an estimated US$3 million before it was taken down by authorities,[6] and Cryptowall, which was estimated by the US Federal Bureau of Investigation (FBI) to have accrued over $18m by June 2015.[7]

Operation

Ransomware typically propagates as a trojan, entering a system through, for example, a downloaded file or a vulnerability in a network service. The program then runs a payload, which typically takes the form of a scareware program. Payloads may display a fake warning purportedly by an entity such as a law enforcement agency, falsely claiming that the system has been used for illegal activities, contains content such as pornography and "pirated" media, or runs a non-genuine version of Microsoft Windows.[8][9][10]

Some payloads consist simply of an application designed to lock or restrict the system until payment is made, typically by setting the Windows Shell to itself,[11] or even modifying the master boot record and/or partition table to prevent the operating system from booting until it is repaired.[12] The most sophisticated payloads encrypt files,[13][14][15] with many using strong encryption to encrypt the victim's files in such a way that only the malware author has the needed decryption key.

Payment is virtually always the goal, and the victim is coerced into paying for the ransomware to be removed—which may or may not actually occur—either by supplying a program that can decrypt the files, or by sending an unlock code that undoes the payload's changes. A key element in making ransomware work for the attacker is a convenient untraceable payment system. A range of such payment methods have been used, including: wire transfer, premium-rate text messages,[16] online payment voucher service such as Ukash or Paysafecard,[2][17][18] and the digital currency Bitcoin.[19][20][21]

History

Encrypting ransomware

The first known ransomware was the 1989 "AIDS" trojan (also known as "PC Cyborg") written by Joseph Popp, which triggered a payload claiming that the user's license to use a certain piece of software had expired, encrypted file names on the hard drive, and required the user to pay US$189 to "PC Cyborg Corporation" for the means to unlock the system. Popp was declared mentally unfit to stand trial for his actions, but he promised to donate the profits from the malware to fund AIDS research.[22] The notion of using public key cryptography for such attacks was introduced in 1996 by Adam L. Young and Moti Yung. The two showed that the AIDS Trojan was ineffective due to its use of symmetric cryptography, since the decryption key can be extracted from the code of the AIDS Trojan, and implemented an experimental proof-of-concept cryptovirus on a Macintosh SE/30 that used RSA and TEA to hybrid encrypt the victim's data. Young and Yung referred to this attack as being "cryptoviral extortion", an overt attack that is part of a larger class of attacks in a field called cryptovirology, which encompasses both overt and covert attacks.[13] The attack described by Young and Yung in IEEE S&P 1996 has the attacker extort e-money from the victim, "A specialized cryptovirus could be designed to search for e-money notes and encrypt them. In this way, the virus writer can effectively hold all of the money ransom until half of it is given to him" (page 135).

Examples of extortionate ransomware became prominent in May 2005.[23] By mid-2006, trojans such as Gpcode, TROJ.RANSOM.A, Archiveus, Krotten, Cryzip, and MayArchive began utilizing more sophisticated RSA encryption schemes, with ever-increasing key-sizes. Gpcode.AG, which was detected in June 2006, was encrypted with a 660-bit RSA public key.[24] In June 2008, a variant known as Gpcode.AK was detected. Using a 1024-bit RSA key, it was believed large enough to be computationally infeasible to break without a concerted distributed effort.[25][26][27][28]

Encrypting ransomware returned to prominence in late 2013 with the propagation of CryptoLocker—using the Bitcoin digital currency platform to collect ransom money. In December 2013, ZDNet estimated based on Bitcoin transaction information that between 15 October and 18 December, the operators of CryptoLocker had procured about US$27 million from infected users.[29] The CryptoLocker technique was widely copied in the months following, including CryptoLocker 2.0 (though not to be related to CryptoLocker), CryptoDefense (which initially contained a major design flaw that stored the private key on the infected system in a user-retrievable location, due to its use of Windows' built-in encryption APIs),[20][30][31][32] and the August 2014 discovery of a trojan specifically targeting network-attached storage devices produced by Synology.[33] A variant of encrypting ransomware dubbed RansomWeb[34] wherein entire websites are compromised and encrypted was first reported in late 2014 by High-Tech Bridge.[34]

An analysis of the various encryption techniques used by different ransomware programs, the vulnerabilities that some have, and possible methods of protection was published in 2015.[35]

Non-encrypting ransomware

In August 2010, Russian authorities arrested ten individuals connected to a ransomware trojan known as WinLock. Unlike the previous Gpcode trojan, WinLock did not use encryption. Instead, WinLock trivially restricted access to the system by displaying pornographic images, and asked users to send a premium-rate SMS (costing around US$10) to receive a code that could be used to unlock their machines. The scam hit numerous users across Russia and neighboring countries—reportedly earning the group over US$16 million.[10][36]

In 2011, a ransomware trojan surfaced that imitated the Windows Product Activation notice, and informed users that a system's Windows installation had to be re-activated due to "[being a] victim of fraud". An online activation option was offered (like the actual Windows activation process), but was unavailable, requiring the user to call one of six international numbers to input a 6-digit code. While the malware claimed that this call would be free, it was routed through a rogue operator in a country with high international phone rates, who placed the call on hold, causing the user to incur large international long distance charges.[8]

In February 2013, a ransomware trojan based on the Stamp.EK exploit kit surfaced; the malware was distributed via sites hosted on the project hosting services SourceForge and GitHub that claimed to offer "fake nude pics" of celebrities.[37] In July 2013, an OS X-specific ransomware trojan surfaced, which displays a web page that accuses the user of downloading pornography. Unlike its Windows-based counterparts, it does not block the entire computer, but simply exploits the behavior of the web browser itself to frustrate attempts to close the page through normal means.[38]

In July 2013, a 21-year-old man from Virginia, whose computer coincidentally did contain pornographic photographs of underaged girls with whom he had conducted sexualized communications, turned himself in to police after receiving and being deceived by ransomware purporting to be an FBI message accusing him of possessing child pornography. An investigation discovered the incriminating files, and the man was charged with child sexual abuse and possession of child pornography.[39] In January 2016 the existence of ransomware that threatens to distribute information on an individual's browsing history was revealed.[40]

Notable examples

Reveton

A Reveton payload, fraudulently claiming that the user must pay a fine to the Metropolitan Police Service

In 2012, a major ransomware trojan known as Reveton began to spread. Based on the Citadel trojan (which itself, is based on the Zeus trojan), its payload displays a warning purportedly from a law enforcement agency (a characteristic referred to as the "police trojan" or "cop trojan"), claiming that the computer has been used for illegal activities, such as downloading pirated software or child pornography.[41] The warning informs the user that to unlock their system, they would have to pay a fine using a voucher from an anonymous prepaid cash service such as Ukash or Paysafecard. To increase the illusion that the computer is being tracked by law enforcement, the screen also displays the computer's IP address, while some versions display footage from a victim's webcam to give the illusion that the user is being recorded.[2][42]

Reveton initially began spreading in various European countries in early 2012.[2] Variants were localized with templates branded with the logos of different law enforcement organizations based on the user's country; for example, variants used in the United Kingdom contained the branding of organizations such as the Metropolitan Police Service, the collection society PRS for Music (which specifically accused the user of illegally downloading music), and the Police National E-Crime Unit.[43] In a statement warning the public about the malware, the Metropolitan Police clarified that they would never lock a computer in such a way as part of an investigation.[2][9]

In May 2012, Trend Micro threat researchers discovered templates for variations for the United States and Canada, suggesting that its authors may have been planning to target users in North America.[44] By August 2012, a new variant of Reveton began to spread in the United States, claiming to require the payment of a $200 fine to the FBI using a MoneyPak card.[3][4][42] In February 2013, a Russian citizen was arrested in Dubai by Spanish authorities for his connection to a crime ring that had been using Reveton; ten other individuals were arrested on money laundering charges.[45] In August 2014, Avast Software reported that it had found new variants of Reveton that also distribute password stealing malware as part of its payload.[46]

CryptoLocker

Main article: CryptoLocker

Encrypting ransomware reappeared in September 2013 with a trojan known as CryptoLocker, which generated a 2048-bit RSA key pair and uploaded in turn to a command-and-control server, and used to encrypt files using a whitelist of specific file extensions. The malware threatened to delete the private key if a payment of Bitcoin or a pre-paid cash voucher was not made within 3 days of the infection. Due to the extremely large key size it uses, analysts and those affected by the trojan considered CryptoLocker extremely difficult to repair.[19][47][48][49] Even after the deadline passed, the private key could still be obtained using an online tool, but the price would increase to 10 BTC—approximately US$2300 as of November 2013.[50][51]

CryptoLocker was isolated by the seizure of the Gameover ZeuS botnet, as officially announced by the U.S. Department of Justice on June 2, 2014. The Department of Justice also publicly issued an indictment against the Russian hacker Evgeniy Bogachev for his alleged involvement in the botnet.[52][53] It was estimated that at least US$3 million was extorted with the malware before the shutdown.[6]

CryptoLocker.F and TorrentLocker

In September 2014, a wave of ransomware trojans surfaced that first targeted users in Australia, under the names CryptoWall and CryptoLocker (which is, as with CryptoLocker 2.0, unrelated to the original CryptoLocker). The trojans spread via fraudulent e-mails claiming to be failed parcel delivery notices from Australia Post; to evade detection by automatic e-mail scanners that follow all links on a page to scan for malware, this variant was designed to require users to visit a web page and enter a CAPTCHA code before the payload is actually downloaded, preventing such automated processes from being able to scan the payload. Symantec determined that these new variants, which it identified as CryptoLocker.F, were again, unrelated to the original CryptoLocker due to differences in their operation.[54][55] A notable victim of the trojans was the Australian Broadcasting Corporation; live programming on its television news channel ABC News 24 was disrupted for half an hour and shifted to Melbourne studios due to a CryptoWall infection on computers at its Sydney studio.[56][57][58]

Another trojan in this wave, TorrentLocker, initially contained a design flaw comparable to CryptoDefense; it used the same keystream for every infected computer, making the encryption trivial to overcome. However, this flaw was later fixed.[30] By late-November 2014, it was estimated that over 9,000 users had been infected by TorrentLocker in Australia alone, trailing only Turkey with 11,700 infections.[59]

Cryptowall

Another major ransomware trojan targeting Windows, Cryptowall, first appeared in 2014. One strain of Cryptowall was distributed as part of a malvertising campaign on the Zedo ad network in late-September 2014 that targeted several major websites; the ads redirected to rogue websites that used browser plugin exploits to download the payload. A Barracuda Networks researcher also noted that the payload was signed with a digital signature in an effort to appear trustworthy to security software.[60] Cryptowall 3.0 used a payload written in JavaScript as part of an email attachment, which downloads executables disguised as JPG images. To further evade detection, the malware creates new instances of explorer.exe and svchost.exe to communicate with its servers. When encrypting files, the malware also deletes volume shadow copies, and installs spyware that steals passwords and Bitcoin wallets.[61]

The FBI reported in June 2015 that nearly 1,000 victims had contacted the bureau's Internet Crime Complaint Center to report Cryptowall infections, and estimated losses of at least $18 million.[7]

The most recent version, Cryptowall 4.0, enhanced its code to avoid antivirus detection, and encrypts not only the data in files but also the file names.[62]

KeRanger

Main article: KeRanger

KeRanger is the first malware and ransomware on the OS X operating system. It encrypts the Mac user's files then demands a sum of one Bitcoin to decrypt the files. It appeared on March 2016. There is an executable in the .DMG that is disguised as a Rich Text File. The virus sleeps for three days, then starts to encrypt the files. It adds a text document for instructions on how to decrypt the files. It uses 2048-RSA public key to encrypt the files. It actually is Linux.Encoder.1 rebuilt for OS X.

RSA4096

RSA4096 is the latest iteration of ransomware to encrypt personal computers and connected devices. It first appeared in 2015 and like all malware uses the 2 key system of public and private keys. Like all other ransomware decryption requires purchasing private keys using Bitcoins bought through brokers in the dark web of which there is no guarantee payment results in obtaining those keys. There are variants of this virus, of which most are unbreakable. Depending on the variant it adds various extensions to your files together with the ransom note. The only method to recover from such an attack is through restoring files from an external disc or purchasing Bitcoins. The cost of Bitcoins has increased significantly over the years which has increased the value of the ransom. At time of writing the ransom is about £300 thousand.

Manamecrypt (CryptoHost)[63]

It states that it encrypts your data and then demands a ransom of .33 bitcoins or approximately 140 USD to get your files back. In reality, though, your data is not encrypted, but rather copied into a password protected RAR archive. Thankfully, the password created by this infection is easily discovered so infected users can get their files back.

When CryptoHost infects the victim's computer it will move certain data files into a password protected RAR archive located in the C:\Users\[username]\AppData\Roaming folder. This file will have a 41 character name and no extension.

CryptoHost is currently being bundled with an uTorrent installer that when installed extracts the cryptohost.exe file to the %AppData% folder and executes it.

Ransomware as a service

Dark web vendors have increasingly started to offer the technology as a service. Brands include the now defunct 'Tox'[64] and 'Encryptor RaaS'.[65]

Mitigation

As with other forms of malware, security software might not detect a ransomware payload, or, especially in the case of encrypting payloads, only after encryption is underway or complete, particularly if a new version unknown to the protective software is distributed.[66] If an attack is suspected or detected in its early stages, it takes some time for encryption to take place; immediate removal of the malware (a relatively simple process) before it has completed would stop further damage to data, without salvaging any already lost.[67][68] Security experts have suggested precautionary measures for dealing with ransomware. Using software or other security policies to block known payloads from launching will help to prevent infection, but will not protect against all attacks. Keeping backups of data stored in locations inaccessible to the infected computer — the malware may encrypt, for example, a USB backup if it is connected to the computer[19][69]—will allow data to be restored to its state at backup time. Ransomware that makes the computer unusable without encrypting files can be overcome by those with sufficient expertise, or by some software for non-experts.

While threats and ransomware attacks cannot be eliminated, use of the defense-in-layers security strategy is the best approach in reducing the chance of devices getting infected with the malware. Defense-in-layers advocates applying security measures in separate but overlapping protections to ensure the implementation of a solid security posture. The security layers are designed to complement each other by ensuring that a vulnerability which is not mitigated in one layer is mitigated by a different control available in another layer. For example, one strategy includes the following five layers:[1] 1. Develop a Comprehensive But Self-Contained Policy 2. Content Filtering Proxy for Web and Mail Traffic 3. Limited-Mode Access 4. Enabling AppLocker 5. Continuous Awareness Training

In popular culture

Much of Neal Stephenson's novel Reamde focuses on a ransomware attack and its consequences.[70]

See also

References

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  2. 1 2 3 4 5 Dunn, John E. "Ransom Trojans spreading beyond Russian heartland". TechWorld. Retrieved 10 March 2012.
  3. 1 2 "New Internet scam: Ransomware...". FBI. 9 August 2012.
  4. 1 2 "Citadel malware continues to deliver Reveton ransomware...". Internet Crime Complaint Center (IC3). 30 November 2012.
  5. ↑ "Update: McAfee: Cyber criminals using Android malware and ransomware the most". InfoWorld. Retrieved 16 September 2013.
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  12. ↑ "And Now, an MBR Ransomware". SecureList (Kaspersky Lab). Retrieved 10 March 2012.
  13. 1 2 Young, A.; M. Yung (1996). Cryptovirology: extortion-based security threats and countermeasures. IEEE Symposium on Security and Privacy. pp. 129–140. doi:10.1109/SECPRI.1996.502676. ISBN 0-8186-7417-2.
  14. ↑ Adam Young (2005). Zhou, Jianying; Lopez, Javier, eds. "Building a Cryptovirus Using Microsoft's Cryptographic API". Information Security: 8th International Conference, ISC 2005 (Springer-Verlag). pp. 389–401.
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  42. 1 2 "Reveton Malware Freezes PCs, Demands Payment". InformationWeek. Retrieved 16 August 2012.
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  62. ↑ Andra Zaharia (2015-11-05). "Security Alert: CryptoWall 4.0 – new, enhanced and more difficult to detect". HEIMDAL. Retrieved 2016-01-05.
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  64. ↑ Brook, Chris (4 June 2015). "Author Behind Ransomware Tox Calls it Quits, Sells Platform". Retrieved 6 August 2015.
  65. ↑ Dela Paz, Roland (29 July 2015). "Encryptor RaaS: Yet another new Ransomware-as-a-Service on the Block". Retrieved 6 August 2015.
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  70. ↑ Stephenson, Neal (September 20, 2011). Reamde. William Morrow. ISBN 978-0-06-197796-1.

Further reading

External links

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