CVE-2025-61925 Overview
CVE-2025-61925 affects the Astro web framework in versions prior to 5.14.2. Astro reflects the value of the X-Forwarded-Host header in output when using Astro.url without validation. A malicious request can supply a spoofed X-Forwarded-Host header that differs from the legitimate Host header, and Astro returns the attacker-controlled value. This impacts applications running Astro in on-demand or dynamic rendering mode, particularly when placed behind a caching proxy. The vulnerability is categorized under [CWE-470] Use of Externally-Controlled Input to Select Classes or Code. Version 5.14.2 contains a fix.
Critical Impact
Attackers can poison cached pages with malicious canonical links, login form URLs, or registration endpoints, redirecting users and potentially harvesting credentials.
Affected Products
- Astro framework versions prior to 5.14.2
- Applications using Astro.url in on-demand or dynamic rendering mode
- Astro deployments behind caching proxies (nginx, CDNs, reverse proxies)
Discovery Timeline
- 2025-10-10 - CVE-2025-61925 published to NVD
- 2026-06-17 - Last updated in NVD database
Technical Details for CVE-2025-61925
Vulnerability Analysis
Astro's Astro.url accessor exposes the current request URL to templates and server code. The framework builds this URL by reading the X-Forwarded-Host request header when present. Astro does not validate this header against an allowlist of trusted domains before reflecting it back into rendered output.
Developers commonly use Astro.url to generate canonical links, absolute URLs for social sharing, and form action targets for login or registration flows. When the reflected host is attacker-controlled, these outputs point at attacker infrastructure. Behind a caching proxy, the poisoned response can be served to subsequent legitimate users, broadening the impact from a single-victim attack to a persistent one.
Root Cause
The root cause is trusting the X-Forwarded-Host header without validation. Many peer frameworks maintain an allowlist of trusted proxy-supplied hosts or avoid reflecting the header into response content. Astro accepted the header value verbatim and used it to construct Astro.url.
Attack Vector
An attacker sends a crafted HTTP request to the Astro origin server or through the caching layer. The request carries a legitimate Host header matching the target site and an X-Forwarded-Host header pointing to an attacker-controlled domain. Astro builds Astro.url from the forwarded header, and the rendered HTML includes attacker-controlled canonical tags, form actions, or absolute links. A caching proxy stores the poisoned response and serves it to other visitors until the cache entry expires.
The vulnerability requires no authentication and can be triggered remotely over the network. See the GitHub Security Advisory for further technical detail and the proof-of-concept repository demonstrating the issue.
Detection Methods for CVE-2025-61925
Indicators of Compromise
- HTTP requests where the X-Forwarded-Host header value does not match the Host header or any expected domain
- Cached HTML responses containing canonical link tags, form actions, or absolute URLs referencing unexpected external domains
- Outbound referrer traffic from users to unknown domains originating from your application's login or registration pages
- Access logs showing repeated requests from a single source with anomalous X-Forwarded-Host values
Detection Strategies
- Inspect reverse proxy and CDN logs for X-Forwarded-Host values that fall outside the set of legitimate application domains
- Deploy content integrity monitoring on rendered pages to detect unexpected changes in <link rel="canonical"> and form action URLs
- Add web application firewall rules that flag requests where X-Forwarded-Host and Host headers diverge
Monitoring Recommendations
- Enable verbose request header logging at the edge to capture Host and X-Forwarded-Host pairs for forensic analysis
- Monitor cache hit patterns for pages that reference Astro.url to identify potential cache poisoning
- Alert on outbound authentication traffic from application pages to unrecognized third-party domains
How to Mitigate CVE-2025-61925
Immediate Actions Required
- Upgrade Astro to version 5.14.2 or later across all environments running dynamic or on-demand rendering
- Audit application source for uses of Astro.url and confirm the values rendered downstream cannot be trusted until the patch is deployed
- Purge caching proxy and CDN caches after patching to remove any poisoned responses currently in circulation
Patch Information
Astro version 5.14.2 contains the fix. Upgrade the astro dependency in package.json and redeploy. Refer to the GitHub Security Advisory GHSA-5ff5-9fcw-vg88 for release notes and remediation guidance.
Workarounds
- Configure the reverse proxy (nginx, HAProxy, CDN) to strip incoming X-Forwarded-Host headers from client requests before they reach the Astro origin
- Override X-Forwarded-Host at the proxy layer with the trusted application hostname on every forwarded request
- Restrict caching for pages that emit Astro.url output until the upgrade is complete, or vary cache keys on Host and validate them against an allowlist
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
