SES is a JavaScript environment that allows safe execution of arbitrary programs in Compartments. In version 0.18.0 prior to 0.18.7, 0.17.0 prior to 0.17.1, 0.16.0 prior to 0.16.1, 0.15.0 prior to 0.15.24, 0.14.0 prior to 0.14.5, an 0.13.0 prior to 0.13.5, there is a hole in the confinement of guest applications under SES that may manifest as either the ability to exfiltrate information or execute arbitrary code depending on the configuration and implementation of the surrounding host.
Guest program running inside a Compartment with as few as no endowments can gain access to the surrounding host’s dynamic import by using dynamic import after the spread operator, like {...import(arbitraryModuleSpecifier)}.
On the web or in web extensions, a Content-Security-Policy following ordinary best practices likely mitigates both the risk of exfiltration and execution of arbitrary code, at least limiting the modules that the attacker can import to those that are already part of the application. However, without a Content-Security-Policy, dynamic import can be used to issue HTTP requests for either communication through the URL or for the execution of code reachable from that origin.
Within an XS worker, an attacker can use the host’s module system to the extent that the host has been configured. This typically only allows access to module code on the host’s file system and is of limited use to an attacker.
Within Node.js, the attacker gains access to Node.js’s module system. Importing the powerful builtins is not useful except insofar as there are side-effects and tempered because dynamic import returns a promise. Spreading a promise into an object renders the promises useless. However, Node.js allows importing data URLs, so this is a clear path to arbitrary execution.
Versions 0.18.7, 0.17.1, 0.16.1, 0.15.24, 0.14.5, and 0.13.5 contain a patch for this issue. Some workarounds are available. On the web, providing a suitably constrained Content-Security-Policy mitigates most of the threat. With XS, building a binary that lacks the ability to load modules at runtime mitigates the entirety of the threat. That will look like an implementation of fxFindModule in a file like xsPlatform.c that calls fxRejectModuleFile.
What the EG score is made of (scorer v4.0: the three questions the 0–10 score mixes, published apart · methodology)
The EG score (9.8): severity, escalated by confirmed exploitation. This CVE's 9.8 is its impact severity (EG Severity), not escalated.
- EG Severity
- 9.8 CRITICALCVSS-B, impact only: no KEV listing, EPSS or EG-KEV tier raises it.GitHub Security Advisory CVSS
- EG Likelihood
- 1.3% within 30 daysSource: FIRST EPSS (model v2026.06.15, score date 2026-11-02). FIRST's exploitation probability, not an EchelonGraph model.
- Confirmed exploitation
- None on record (CISA KEV, EG-KEV Tier 1)Reported apart from the likelihood: an observed fact, not a probability.
- EG Priority
- SSVC Track* at medium mission impactTrack at low, Track* at medium and Attend at high mission impact.CISA BOD 26-04: 3 days if the affected system is publicly exposed; 60 days if it is not.Each input and its source, and whom BOD 26-04 binds: the SSVC and BOD 26-04 blocks below.
SSVC (CISA's decision table, applied by EchelonGraph)Track at low, Track* at medium and Attend at high mission impact.
A fix is available. Apply it within your standard update timelines at low or medium mission impact and sooner than that at high.
Exploitation public PoC (CISA Vulnrichment) · Automatable yes (CISA Vulnrichment) · Technical impact total (CISA Vulnrichment). All three are CISA's SSVC values (Vulnrichment). EchelonGraph applied CISA's decision table to them; CISA publishes SSVC inputs and the table, not a decision for each CVE. Mission impact is CISA's Mission & Well-being decision point, and only you can judge it. CISA's table makes it high when Mission Prevalence is Essential — the vulnerable component "directly provides capabilities that constitute at least one MEF for at least one entity" (MEF: mission essential function) — or when Public Well-Being Impact is Irreversible: "multiple fatalities are likely", the cyber-physical system "is likely lost or destroyed", "extreme or serious externalities" are imposed on other parties, or social systems such as elections or the financial grid "are destabilized and potentially collapse". CISA's decision table
BOD 26-04 (CISA's remediation timeline, Table 1)3 days if the affected system is publicly exposed; 60 days if it is not.
The score's inputs: In CISA KEV no (CISA's KEV catalog) · Automatable yes (CISA Vulnrichment) · Technical impact total (CISA Vulnrichment). Whether your system is publicly exposed is yours to answer. BOD 26-04 binds US Federal Civilian Executive Branch agencies; for anyone else it is CISA's published timeline, a reference rather than an obligation. The directive · how EchelonGraph applies it