Scenario 10: Cyber weapons review

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State A develops new malware capable of physical destruction of enemy military equipment. However, if released, it is also expected to result in the temporary impairment of the use of civilian cyber infrastructure through which it may spread in order to reach its target. This scenario considers State obligations to conduct a weapons review with respect to cyber capabilities of this kind potentially already in peacetime, well before they may actually be deployed in time of armed conflict. In particular, it examines whether such malware constitutes a weapon that is inherently indiscriminate and therefore prohibited by IHL.

1 Scenario

1.1 Keywords

Article 36, cyber weapons, indiscriminate attack, international humanitarian law, malware, methods and means of warfare, weapons review, Stuxnet

1.2 Facts

[F1] State A develops new sophisticated malware designed to weaken the military capacity of its adversaries in times of armed conflict. The software is capable of replicating itself through cyber infrastructure.

[F2] Once installed in a host system, the malware assesses it for the presence of a specific programmable logic controller (PLC) used by several States for the purposes of automated maintenance of military equipment. If it does not detect this specific PLC in a given host system, it attempts to further spread through any connected networks and then it shuts itself down in that particular host system. However, if the detection is positive, the malware uses a vulnerability in the PLC to slightly alter the maintenance process.

[F3] The effect of this alteration is that instead of servicing the equipment in question, the maintenance machines damage it and thus render it unusable. Tests in controlled environment show that whenever the malware is installed in a host system, it causes it to significantly slow down for a short period of time. However, it is not expected to cause physical damage unless the target PLC is detected in a specific host system.

1.3 Examples

2 Legal analysis

For a general overview of the structure of analysis in this section, see Note on the structure of articles.

[L1] The analysis in this scenario examines State obligations to conduct a weapons review with respect to cyber capabilities they may develop or acquire. In the first place, it considers whether malware capable of physical destruction qualifies as a weapon. This is especially significant because classifying a capability as a weapon means that it must comply with the relevant rules of IHL. The analysis then zones in on the question whether such malware would be considered as inherently indiscriminate and therefore prohibited by IHL.

Legal review of cyber weapons
Legal review of cyber weapons.svg
Although IHL is primarily designed to govern situations of armed conflict, some of its rules also apply in times of peace,[1] including the obligation to respect and ensure respect for IHL, codified in Common Article 1 to the Geneva Conventions and generally considered to reflect customary international law.[2] The obligation in turn implies a duty of each State to ensure that means of warfare available to it comply with the relevant rules of IHL.[3] In addition, Article 36 of Additional Protocol I provides that “[i]n the study, development, acquisition or adoption of a new weapon, means or method of warfare,” States must determine whether its employment would be prohibited under any rule of international law.[4] It has been argued that the Article 36 obligation represents customary international law,[5] but this view is not universally accepted.[6]

To begin with, the mere fact of a weapon’s novelty or its reliance on new technology does not automatically mean that the weapon is illegal.[7] Similarly, the lack of general practice by States in using the new weapon is irrelevant as to its legality under IHL.[8] Additionally, all States remain subject to the so-called Martens Clause,[9] which reinforces the notion that the lawfulness of a new means of warfare must be assessed under customary international law according to the principles of humanity and the requirements of the public conscience.[10] In determining the weapon’s lawfulness, the State in question must therefore consider whether there is any specific prohibition under IHL that would bar the State from using it in practice.[11] It is unsettled whether this consideration must take the form of a formal legal review approximating that required by Article 36 or whether it would suffice for the State to seek the advice of a legal advisor at the relevant level of command.[12]

Although the precise definition of a “cyber weapon” is unsettled as yet,[13] at the very least, all cyber means capable of conducting “attacks” as understood in IHL, that is, acts of violence against the adversary,[14] should be considered to qualify as cyber weapons,[15] thus falling under the principle that IHL applies to “all forms of warfare and to all kinds of weapons, those of the past, those of the present and those of the future”.[16] For States Parties to Additional Protocol I, the obligation extends to the early stages of studying and developing a new cyber capability; these States must conduct a formal legal review; and the scope of the review includes the entirety of international law, not just rules of IHL.[17]

Therefore, States must first consider whether the cyber weapon in question would violate an express specific prohibition on its use.[18] Although no prohibitions of this kind exist at present, this may well change in the future. In particular, there is recurring talk of States entering into “cyber arms control treaties” or agreeing to specific limitations on the development and use of cyber offensive capabilities. If formulated as binding prohibitions, these may prevent States from utilizing capabilities falling under the remit of such rules.

States must then consider whether the employment of the cyber weapon in question would be restricted by any of the relevant rules of IHL. These include, in particular, the prohibition of means of warfare that are of a nature to cause superfluous injury or unnecessary suffering[19] and the prohibition of means of warfare that are by nature indiscriminate.[20] However, the requirement that the weapon in question would have to cause the prohibited effects by its “nature” is quite restrictive as most means of warfare can be used in a number of different ways. As long as the weapon can be employed in a lawful way, its use in abstract would not be prohibited by these rules of IHL. Accordingly, Tallinn Manual 2.0 notes that both prohibitions would only rarely be violated by cyber means.[21]

[L2] In the present scenario, the malware developed by State A would qualify as a “cyber weapon” due to its ability to produce physical destruction, which is an effect that qualifies as “violence against the adversary”.[22] State A would accordingly be under a duty to ensure that the use of this malware complies with its international obligations. This is so irrespective of whether State A is currently involved in any armed conflict or not. If State A has ratified Additional Protocol I, its duties would additionally extend to conducting a formal legal review, which would include the assessment of the malware’s compliance with all applicable rules of international law.

[L3] There is no indication that the malware’s employment would cause any injury to persons, thus rendering inapplicable the rules on superfluous injury or unnecessary suffering. Means and methods of cyber warfare will only in the rarest cases violate the principle of superfluous injury or unnecessary suffering.[23] By contrast, the fact that the malware does not distinguish between civilian and military infrastructure in order to reach its intended target raises questions of its compatibility with the prohibition of inherently indiscriminate means of warfare.

[L4] A weapon is considered indiscriminate by nature if it either cannot be directed at a specific military objective,[24] or if its effects cannot be limited as required by IHL and it is thus of a nature to strike military objectives and civilian objects without distinction.[25] State A’s malware appears to pass the first condition given that it is specifically designed to target the PLCs controlling military equipment, which would normally qualify as a military objective under IHL.[26]

[L5] However, with respect to the second condition, it is clear that the effects of the malware are not limited solely to the intended military objective and, moreover, that these effects are not wholly under State A’s control. Once released, the malware can spread through civilian infrastructure and can be expected to temporarily impair the ordinary use of infected civilian host systems. Accordingly, State A must assess whether the safeguards built in the malware are sufficient to prevent reverberating harmful effects going beyond the control of the attacker.[27]

[L6] In this regard, States may consider including in the malware a “kill switch” which, if activated, immediately stops the malware from spreading further. The presence of an effective “kill switch” ensures that the attacker is capable of limiting the effects of the malware in particular circumstances. Accordingly, the malware would not qualify as an inherently indiscriminate cyber weapon.[28] Of course, it would still be capable of being used in an indiscriminate manner, but that is an issue that must be considered in relation to each specific attack rather than during the ex ante legal review.

[L7] Overall, the assessment must take into account all relevant circumstances and the reasonable expectations of the deploying State.[29] In this regard, the temporary effects on civilian infrastructure occasioned by the spread of the virus are likely insufficient to indicate the illegality of the malware. This is because mere inconvenience or annoyance is not considered as collateral damage to civilian objects in the proportionality calculus.[30] As long as the release and proliferation of the malware is not expected, or should not reasonably be expected, to cause damage to civilian and military systems without distinction, it would thus likely pass the second condition, too.[31]

3 Checklist

  • Is the State in question a State party to Additional Protocol I?
  • Does the malware qualify as a weapon under IHL?
  • Does the malware violate any specific international law prohibition on its use?
  • Is the malware capable of causing injury to persons? If so, is it of a nature to cause superfluous injury or unnecessary suffering?
  • Is the malware by nature indiscriminate?
  • What is the probability that the target PLC would be accidentally discovered in a non-military host system?
  • Does the malware contain a “kill switch” which, if activated, would stop the malware from spreading further?

4 Appendixes

4.1 See also

4.2 Notes and references

  1. See, eg, Arts 23, 44, 47 GC I; Art 127 GC III; Art 144 GC IV; Arts 6, para 1, and 83, para 1 AP I; Art. 7 AP III.
  2. Robin Geiss, ‘The Obligation to Respect and to Ensure Respect for the Conventions’ in Andrew Clapham, Paola Gaeta and Marco Sassòli (eds), The 1949 Geneva Conventions: A Commentary (OUP 2015) 121-22.
  3. Tallinn Manual 2.0, commentary to rule 110, para 2; see also ICRC, International Humanitarian Law and the Challenges of Contemporary Armed Conflicts: Recommitting to Protection in Armed Conflict on the 70th Anniversary of the Geneva Conventions (October 2019) 28 (“In the ICRC’s view, the requirement to carry out legal review of new weapons ... flows from the obligation to ensure respect for IHL under Article 1 common to the Geneva Conventions.”).
  4. Article 36 AP I.
  5. See, eg, Duncan Blake and Joseph S. Imburgia, ‘“Bloodless Weapons”? The need to conduct legal review of certain capabilities and the implications of defining them as “weapons”’, (2010) 66 AFLRev 157, 163–64; see also, William H Boothby, Weapons and the Law of Armed Conflict (2nd edn, OUP 2016) 342-43 (“For states that are not party to AP1, the implied obligation should not necessarily be expressed in the same terms as article 36, but its existence is attested to by the practice of certain states before the adoption of AP1”).
  6. See, Tallinn Manual 2.0, commentary to rule 110, para 2.
  7. See, eg, US DoD Manual, para 6.2.1.
  8. David Wallace, ‘Cyber Weapon Reviews under International Humanitarian Law: A Critical Analysis’ (2018) Tallinn Paper No. 11, 9.
  9. For a modern formulation of the Martens Clause, see Art 1(2) AP I (“In cases not covered by this Protocol or by other international agreements, civilians and combatants remain under the protection and authority of the principles of international law derived from established custom, from the principles of humanity and from dictates of public conscience.”).
  10. David Wallace, ‘Cyber Weapon Reviews under International Humanitarian Law: A Critical Analysis’ (2018) Tallinn Paper No. 11, 9.
  11. David Wallace, ‘Cyber Weapon Reviews under International Humanitarian Law: A Critical Analysis’ (2018) Tallinn Paper No. 11, 10.
  12. See Tallinn Manual 2.0, commentary to rule 110, para 4.
  13. See, eg, Gary D. Brown and Andrew O. Metcalf, ‘Easier Said Than Done: Legal Reviews of Cyber Weapons’ (2014) 7 JNSLP 115, 135 (defining a kinetic and/or a cyber weapon as “an object designed for, and developed or obtained for, the primary purpose of killing, maiming, injuring, damaging or destroying”); Tallinn Manual 2.0, rule 103, para 2 (“cyber weapons are cyber means of warfare that are used, designed, or intended to be used to cause injury to, or death of, persons or damage to, or destruction of, objects”); Air Force Instruction 51-401 (3 August 2018) 13 (defining a cyber capability as “any device, computer program or computer script, including any combination of software, firmware or hardware intended to deny, disrupt, degrade, destroy or manipulate adversarial target information, information systems, or networks”).
  14. Art 49 AP I.
  15. Tallinn Manual 2.0, rule 103, para 2; but see Jeffrey T Biller and Michael N Schmitt, ‘Classification of Cyber Capabilities and Operations as Weapons, Means, or Methods of Warfare’ (2019) 95 Int’l L Stud 179, 218 (arguing that “code used in hostile cyber operations does not qualify as a means of warfare”) and 219 (characterizing “cyber operations as a method of warfare”) (emphasis added).
  16. Legality of the Threat or Use of Nuclear Weapons Case (Advisory Opinion) [1996] ICJ Rep 226, para 86.
  17. Tallinn Manual 2.0, commentary to rule 110, para 6.
  18. Examples of such express prohibitions include the general ban on the use of chemical or biological weapons.
  19. Art 23(e) Hague Regulations; Art 35(2) AP I; ICRC CIHL Study, rule 70; Tallinn Manual 2.0, rule 104.
  20. Art 51(4)(b) AP I; ICRC CIHL Study, rules 12 and 71 ; Tallinn Manual 2.0, rule 105; see also US DoD Manual, para 16.6 (“a legal review of the acquisition or procurement of a weapon that employs cyber capabilities likely would assess whether the weapon is inherently indiscriminate”).
  21. Tallinn Manual 2.0, commentary to rule 104, para 6; ibid, rule 105, para 7.
  22. Art 49(1) AP I.
  23. Cf. Tallinn Manual 2.0, commentary to rule 104, para 6 (proposing, in this regard, the example of remotely taking control of a target’s pacemaker device to stop his “heart and then reviving him multiple times before finally killing him”).
  24. Art 51(4)(b) AP I.
  25. Art 51(4)(c) AP I.
  26. See Art 52(2) AP I (“In so far as objects are concerned, military objectives are limited to those objects which by their nature, location, purpose or use make an effective contribution to military action and whose total or partial destruction, capture or neutralization, in the circumstances ruling at the time, offers a definite military of advantage.”).
  27. Cf. Tallinn Manual 2.0, commentary to rule 105, para 4 (noting that malware that would inevitably and harmfully spread into civilian networks in a manner beyond the control of the attacker would violate this prohibition).
  28. Cf. also Tallinn Manual 2.0, commentary to rule 105, para 4 (“To the extent the effects of the means or method of warfare can be limited in particular circumstances, it does not violate [this prohibition].”).
  29. Tallinn Manual 2.0, commentary to rule 104, para 5.
  30. Tallinn Manual 2.0, commentary to rule 105, para 5.
  31. See also Tallinn Manual 2.0, commentary to rule 105, para 5 (considering that “Stuxnet-like malware that spreads widely into civilian systems, but only damages specific enemy technical equipment” would not violate this prohibition).

4.3 Bibliography

4.4 Contributions

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