Symfony XML Entity Expansion security vulnerability
Symfony 2.0.11 carried a [similar] XXE security fix, however, on review of ZF2 I also noted a vulnerability to XML Entity Expansion (XEE) attacks whereby all extensions making use of libxml2 have no defense against XEE Quadratic Blowup Attacks. The vulnerability is a function of there being no current method of disabling custom entities in PHP (i.e. defined internal to the XML document without using external entities). In a QBA, a long entity can be defined and then referred to multiple times in document elements, creating a memory sink with which Denial Of Service attacks against a host's RAM can be mounted. The use of the LIBXML_NOENT or equivalent option in a dependent extension amplified the impact (it doesn't actually mean "No Entities"). In addition, libxml2's innate defense against the related Exponential or Billion Laugh's XEE attacks is active only so long as the LIBXML_PARSEHUGE is NOT set (it disables libxml2's hardcoded entity recursion limit). No instances of these two options were noted, but it's worth referencing for the future.
Consider this (non-fatal) example:
<?xml version="1.0"?>
<!DOCTYPE data [<!ENTITY a
"aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa">]>
<data>&a;&a;&a;&a;&a;&a;&a;&a;&a;&a;&a;&a;&a;&a;&a;&a;&a;&a;&a;&a;&a;&a;&a;&a;&a;&a;&a;&a;&a;&a;&a;&a;&a;&a;&a;&a;&a;&a;&a;&a;&a;&a;&a;&a;&a;&a;&a;&a;&a;&a;&a;&a;&a;&a;&a;&a;&a;&a;&a;&a;&a;&a;&a;&a;&a;&a;&a;&a;&a;&a;&a;&a;&a;&a;&a;&a;&a;&a;&a;&a;&a;&a;&a;&a;&a;&a;&a;&a;&a;&a;&a;&a;&a;&a;&a;&a;&a;&a;&a;&a;&a;&a;&a;&a;&a;&a;&a;&a;&a;&a;&a;&a;&a;&a;&a;&a;&a;&a;&a;&a;&a;&a;</data>Increase the length of entity, and entity count to a few hundred, and peak memory usage will waste no time spiking the moment the nodeValue for is accessed since the entities will then be expanded by a simple multiplier effect. No external entities required.
...
This can be used in combination with the usual XXE defense of calling libxml_disable_entity_loader(TRUE) and, optionally, the LIBXML_NONET option (should local filesystem access be allowable). The DOCTYPE may be removed instead of rejecting the XML outright but this would likely result in other problems with the unresolved entities.
Software afectado
Haz clic en una tecnología para ver todas sus vulnerabilidades.
| Plataforma | Paquete | Versiones vulnerables | Corregida en |
|---|---|---|---|
| Paquete de Composer | symfony/dependency-injection | >= 2.0.0, < 2.0.17 | 2.0.17 |
Referencias
- https://github.com/symfony/dependency-injection/commit/5c5040c890a8e4085dcd6fa3827f574ab5f71f4c
- https://github.com/FriendsOfPHP/security-advisories/blob/master/symfony/dependency-injection/2012-08-28.yaml
- https://github.com/symfony/dependency-injection
- https://symfony.com/blog/security-release-symfony-2-0-17-released
- Vector CVSS
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H- Debilidad (CWE)
CWE-611- Plataforma
- Composer
- Paquete
symfony/dependency-injection- Publicada
- 29.05.2024
- Actualizado
- 11.10.2026 10:22
Fuentes y licencias
OSV / GitHub Advisory Database - GHSA-c636-cg5r-2498 - CC BY 4.0
Historial de vulnerabilidades: symfony/dependency-injection
Todas las vulnerabilidades publicadas de este paquete (Paquete de Composer), de la más reciente a la más antigua. Muestra si es un fallo aislado o un paquete que hay que vigilar.
- Entradas en total
- 2
- Primera → última
- 11.2019 05.2024
- Sin corrección
- 0
- Explotada en ataques
- 0
Distribución por gravedad
- Crítica 1
- Alta 1
Divulgaciones por año
- 2019: 1
- 2020: 0
- 2021: 0
- 2022: 0
- 2023: 0
- 2024: 1
- 2025: 0
- 2026: 0
-
Symfony XML Entity Expansion security vulnerability esta entrada
Identifica las vulnerabilidades de tu aplicación
Con la integración de DockRay y el inventario de software activado, DockRay compara las versiones notificadas de los componentes con las vulnerabilidades conocidas y avisa de las coincidencias confirmadas. La cobertura depende de la tecnología compatible y de los avisos disponibles.