Cross-site scripting in Gatsby - #VU165937
Published: November 11, 2026
Vulnerability identifier: #VU165937
CSH Severity: Low
CVSS v4: 2 [CVSS:4.0/AV:A/AC:L/AT:P/PR:N/UI:A/VC:N/VI:N/VA:N/SC:L/SI:L/SA:N]
CVE-ID: N/A
CWE-ID: CWE-79
Exploitation vector: Adjecent network
Exploit availability:
No public exploit available
Vulnerability details
The vulnerability allows a remote attacker on the local network to execute arbitrary JavaScript in a victim's browser through reflected cross-site scripting.
The vulnerability exists due to missing content-type specification in Gatsby's development server /_gatsby/file endpoint when proxying attacker-controlled responses, allowing browser content sniffing to interpret HTML as a web page. A remote attacker on the local network can trick a victim into opening a crafted URL using the u query parameter to proxy malicious HTML through a development server exposed to an untrusted network.
Affected software
Gatsby
Remediation
Install security update from vendor's website.
Gatsby - addressed in versions 4.10.1, 5.0.1