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Vulnerability Exploitability eXchange (VEX)

CISA has a neat bit of work they recently published, entitled “Vulnerability Exploitability eXchange (VEX) – Status Justifications” (warning: opens to .pdf.).1 Product security teams that adopt VEX could assert the status of specific vulnerabilities in their products. As a result, clients’ security staff could allocate time to remediate actionable vulnerabilities instead of burning time on potential vulnerabilities that product security teams have already closed off or mitigated.

There are a number of different machine-readable status types that are envisioned, including:

  • Component_not_present
  • Vulnerable_code_not_present
  • Vulnerable_code_cannot_be_controlled_by_adversary
  • Vulnerable_code_not_in_execute_path
  • Inline_mitigations_already_exist

CISA’s publication spells out what each status entails in more depth and includes diagrams to help readers understand what is envisioned. However, those same readers need to pay attention to a key caveat, namely, “[t]his document will not address chained attacks involving future or unknown risks as it will be considered out of scope.” Put another way, VEX is used to assess known vulnerabilities and attacks. It should not be relied upon to predict potential threats based on not-yet-public attacks nor new ways of chaining known vulnerabilities. Thus, while it would be useful to ascertain if a product is vulnerable to EternalBlue, today, it would not be useful to predict or assess the exploited vulnerabilities prior to EternalBlue having been made public nor new or novel ways of exploiting the vulnerabilities underlying EternalBlue. In effect, then, VEX is meant to address the known risks associated with N-Days as opposed to risks linked with 0-Days or novel ways of exploiting N-Days.2

For VEX to best work there should be some kind of surrounding policy requirements, such as when/if a supplier falsely (as opposed to incorrectly) asserts the security properties of its product there should be some disciplinary response. This can take many forms and perhaps the easiest relies on economics and not criminal sanction: federal governments or major companies will decline to do business with a vendor found to have issued a deceptive VEX, and may have financial recourse based on contactual terms with the product’s vendor. When or if this economic solution fails then it might be time to turn to legal venues and, if existent approaches prove insufficient, potentially even introduce new legislation designed to further discipline bad actors. However, as should be apparent, there isn’t a demonstrable requirement to introduce legislation to make VEX actionable.

I think that VEX continues work under the current American administration to advance a number of good policies that are meant to better secure products and systems. VEX works hand-in-hand with SBOMs and, also, may be supported by US Executive Orders around cybersecurity.

While Canada may be ‘behind’ the United States we can see that things are potentially shifting. There is currently a consultation underway to regenerate Canada’s cybersecurity strategy and infrastructure security legislation was introduced just prior to Parliament rising for its summer break. Perhaps, in a year’s time, we’ll see stronger and bolder efforts by the Canadian government to enhance infrastructure security with some small element of that recommending the adoption of VEXes. At the very least the government won’t be able to say they lack the legislative tools or strategic direction to do so.


  1. You can access a locally hosted version if the CISA link fails. ↩︎
  2. For a nice discussion of why N-days are regularly more dangerous then 0-Days, see: “N-Days: The Overlooked Cyber Threat for Utilities.” ↩︎