Budibase: Unanchored Regex in `matchers.ts` Allows CSRF Bypass via Query String Injection in Budibase Worker
Date: 2026-06
Affected: npm/@budibase/backend-core
Attack vector: other
Category: vulnerability-disclosure
Severity: Medium
CVE: CVE-2026-48147
CWE: CWE-185
CWE-352
CVSS: 6.5 (CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:N)

### Summary The `buildMatcherRegex()` / `matches()` functions in `packages/backend-core/src/middleware/matchers.ts` share the same structural root cause as the recently patched CVE-2026-31816: route patterns are compiled into **unanchored regular expressions** and tested against `ctx.request.url`, which includes the full query string. The CSRF middleware in the Budibase Worker uses this matching system to decide whether to skip CSRF token validation. An unauthenticated attacker can forge state-changing cross-origin requests against any Worker API endpoint by injecting a public route pattern into the query string, causing the CSRF middleware to skip token validation entirely. This allows actions such as sending admin invites, modifying global configuration, and managing users without a valid CSRF token. CVE-2026-31816 fixed the same unanchored-regex-on-full-URL bug in `server/middleware/utils.ts` but left `backend-core/middleware/matchers.ts` untouched. --- ### Details **Root cause — `packages/backend-core/src/middleware/matchers.ts`:** ```typescript export const buildMatcherRegex = (patterns: EndpointMatcher[]): RegexMatcher[] => { return patterns.map(pattern => { let route = pattern.route // replaces :param segments with /.* const matches = route.match(PARAM_REGEX) if (matches) { for (let match of matches) { const suffix = match.endsWith("/") ? "/" : "" route = route.replace(match, "/.*" + suffix) } } return { regex


Mitigations:

Architectural layers (MAESTRO):