CVE-2026-27829
Published: 26 February 2026
Summary
CVE-2026-27829 is a medium-severity SSRF (CWE-918) vulnerability in Astro \@Astrojs\/Node. Its CVSS base score is 6.5 (Medium).
Operationally, exploitation aligns with the MITRE ATT&CK technique Exploit Public-Facing Application (T1190); ranked at the 19.8th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog; a public proof-of-concept is referenced.
The strongest mitigations our analysis identified are NIST 800-53 AC-4 (Information Flow Enforcement) and SI-10 (Information Input Validation).
Deeper analysis
CVE-2026-27829 is a vulnerability in the Astro web framework, affecting versions 9.0.0 through 9.5.3. The issue resides in Astro's image pipeline, where the `inferSize` option fetches remote images at render time to determine their dimensions without performing domain validation. This allows bypassing the `image.domains` or `image.remotePatterns` restrictions that developers configure to limit fetches to authorized hosts only.
An attacker who can influence the image URL—such as through CMS content or user-supplied data—can exploit this to force the Astro server to fetch content from arbitrary remote hosts. This enables server-side request forgery (SSRF), including against internal network services or cloud metadata endpoints, with a CVSS v3.1 base score of 6.5 (AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:L) and mapping to CWE-918.
The Astro security advisory (GHSA-cj9f-h6r6-4cx2) and corresponding commit (e01e98b063e90d274c42130ec2a60cc0966622c9) confirm that upgrading to version 9.5.4 resolves the issue by enforcing domain validation during `inferSize` fetches.
OWASP Top 10 for Web (2025)
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2026-8785
Vulnerability details
Astro is a web framework. In versions 9.0.0 through 9.5.3, a bug in Astro's image pipeline allows bypassing `image.domains` / `image.remotePatterns` restrictions, enabling the server to fetch content from unauthorized remote hosts. Astro provides an `inferSize` option that fetches remote…
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images at render time to determine their dimensions. Remote image fetches are intended to be restricted to domains the site developer has manually authorized (using the `image.domains` or `image.remotePatterns` options). However, when `inferSize` is used, no domain validation is performed — the image is fetched from any host regardless of the configured restrictions. An attacker who can influence the image URL (e.g., via CMS content or user-supplied data) can cause the server to fetch from arbitrary hosts. This allows bypassing `image.domains` / `image.remotePatterns` restrictions to make server-side requests to unauthorized hosts. This includes the risk of server-side request forgery (SSRF) against internal network services and cloud metadata endpoints. Version 9.5.4 fixes the issue.
- CWE(s)
Related Threats
MITRE ATT&CK Enterprise TechniquesAI
Why these techniques?
SSRF in public-facing Astro image pipeline (bypassing domain restrictions) directly enables exploitation of the web app (T1190) and access to cloud instance metadata endpoints (T1522).
CVEs Like This One
Affected Assets
Mitigating Controls
Mitigating Controls (NIST 800-53 r5) AI
Directly validates image URLs against authorized domains before any fetch occurs, blocking the inferSize bypass that allows arbitrary remote hosts.
Enforces the configured image.domains / image.remotePatterns flow restrictions on outbound fetches, which the vulnerability circumvents during inferSize processing.
Applies boundary protections to restrict unauthorized server-side outbound connections to internal or external hosts, mitigating the resulting SSRF exposure.