EUVD-2026-335352

fkie_cve-2026-59731

Astro is a web framework for content-driven websites. Version 6.4.7 performs authorization decisions on a partially decoded pathname after reaching the iterative URL decoder limit, while later rewrite route matching performs an additional decodeURI() operation and can resolve the request to a protected route. This issue is fixed in version 6.4.8.

GHSA-vj59-8hwv-xxmv — Astro: Authorization Bypass via Decode Iteration Limit and Rewrite Path Canonicalization Mismatch

Affected: npm: astro

# Astro 6.4.7 Authorization Bypass via Decode Iteration Limit and Rewrite Path Canonicalization Mismatch

## Summary

Astro 6.4.7 appears to reintroduce a middleware authorization bypass pattern when a request path is encoded more deeply than the newly introduced iterative URL decoder's maximum decoding depth.

The issue occurs because Astro performs authorization decisions on a partially decoded pathname after reaching a decoding iteration cap, while later route matching logic performs an additional `decodeURI()` operation and resolves the request to a protected route.

As a result, middleware and route matching may operate on different pathname representations, enabling authorization bypasses under specific application patterns.

**Potential CWE:** CWE-647 – Use of Non-Canonical URL Paths for Authorization Decisions

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## Vulnerable Pattern

Middleware authorization sees:

```text /%61dmin ```

Later rewrite route matching sees:

```text /admin ```

This discrepancy allows a request that bypasses middleware checks to subsequently resolve to a protected route.

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## Root Cause

### Iterative Decoding Logic

PR #16967 introduced iterative URI decoding:

```js let iterations = 0;

while (decoded !== pathname && iterations < 10) { pathname = decoded;

try { decoded = decodeURI(pathname); } catch { // decodeURI can fail when a decoded literal '%' forms an // invalid sequence with adjacent characters. break; }

iterations++; }

return decoded; ```

The intent…

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EUVD-2026-335352

fkie_cve-2026-59731

GHSA-vj59-8hwv-xxmv — Astro: Authorization Bypass via Decode Iteration Limit and Rewrite Path Canonicalization Mismatch