CVE-2023-43656: Sandbox escape for instances that have enabled transformation functions in matrix-hookshot

Severity: critical (CVSS 9.0 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.3% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2023-09-27 · updated 2026-06-17
Weakness: CWE-74

Description

matrix-hookshot is a Matrix bot for connecting to external services like GitHub, GitLab, JIRA, and more. Instances that have enabled transformation functions (those that have `generic.allowJsTransformationFunctions` in their config), may be vulnerable to an attack where it is possible to break out of the `vm2` sandbox and as a result Hookshot will be vulnerable to this. This problem is only likely to affect users who have allowed untrusted users to apply their own transformation functions. If you have only enabled a limited set of trusted users, this threat is reduced (though not eliminated). Version 4.5.0 and above of hookshot include a new sandbox library which should better protect users. Users are advised to upgrade. Users unable to upgrade should disable `generic.allowJsTransformationFunctions` in the config.

Affected products

matrix-org matrix-hookshot: before 4.5.0 — fixed in 4.5.0

How to fix

Upgrade to a fixed version: matrix-org matrix-hookshot 4.5.0. Check the vendor advisory for mitigations.

References

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