Symfony 2.0: XML Entity Expansion Lets Small Documents Exhaust Memory

Published as "Symfony XML Entity Expansion security vulnerability"

high Symfony Symfony components · Last reviewed Nov 10, 2026

CVE: No CVE assigned
GHSA: GHSA-q2gc-gg3x-7942
Packagist: PKSA-fc3t-zgzf-rtyg
Reported: May 30, 2024

Lets an attacker use up a server's memory with one small XML document in Symfony 2.0 apps that parse untrusted XML.

Affected and fixed versions

In symfony/symfony. Find the row for the version you run, and update to the release next to it.

If you run	Update to	Support
2.0.0 – 2.0.16	2.0.17

Upgrade

Run the line for the branch you are on.

composer require symfony/symfony:^2.0.17

What this means

An attacker can send a small XML document that grows to a huge size in memory when your app parses it, slowing or crashing the server. This is an XML entity expansion attack, where a few short references in a document expand into a very large amount of text. It's a denial of service, not a data leak.

See Symfony's announcement and the fix.

Who is affected

Apps on symfony/symfony before 2.0.17 that pass XML from users or another untrusted source to a Symfony component that parses it. The fix changed XmlEncoder in the Serializer component, Crawler in DomCrawler, and the XML file loaders of DependencyInjection, Routing, Translation (XliffFileLoader) and Validator.

The file loaders read your own config and translation files, which you control. The exposure is mainly decoding untrusted XML with XmlEncoder or loading it into Crawler.

What to do

Update to 2.0.17. After the update, these components refuse XML that declares its own document type, which is where such entities are defined, and turn off network access while loading XML.

Symfony 2.0 stopped getting fixes long ago, so plan a move to a supported version.

Reported by Pádraic Brady of the Zend Framework team.

Check your app with an agent

Paste this into a coding agent that can read your project, such as Claude Code, Codex or Amp. It checks your composer.lock against the versions above and tells you what to update, without changing anything.

Check whether the PHP project you have access to is affected by this security advisory, and tell me what to update. Do a read-only check: don't edit files, don't run composer update or composer require, and don't try to reproduce the flaw.

Advisory: Symfony 2.0: XML Entity Expansion Lets Small Documents Exhaust Memory (GHSA-q2gc-gg3x-7942)
Details: https://phpnews.net/security/symfony/ghsa-q2gc-gg3x-7942

Affected versions, as Composer constraints:
- symfony/symfony: >=2.0.0,<2.0.17

Fixed releases:
- 2.0.0 – 2.0.16: update to 2.0.17

1. Find every composer.lock in the project outside vendor/ (a monorepo can have one per app) and read the installed version of each package above. Packages installed as dependencies of other packages count too.
2. Compare each installed version with its constraint: "|" separates alternative ranges, and "," means both bounds apply.
3. For each affected install, read "What this means" at https://phpnews.net/security/symfony/ghsa-q2gc-gg3x-7942 and check whether the project meets the conditions it describes (a feature in use, a config value, a driver). Say which conditions you could check and which you couldn't.
4. Report a table: lock file | package | installed version | affected (yes, no or unknown) | conditions met (yes, no or unknown) | update to | evidence. For each affected package, give the command that would fix it, without running it: composer update <package> --with-dependencies when it is only installed as a dependency of another package, or composer require with the fixed version when composer.json requires it directly. If the installed version is on a branch with no fixed release listed, say it needs a move to a newer branch.

Sources

GitHub advisory GHSA-q2gc-gg3x-7942 →

← All Symfony advisories