Symfony Serializer: Data URIs Can Read Any File on the Server

Published as "DataUriNormalizer Opens Data URIs With a Non-Lowercase Scheme as Local Files, Letting a Client Read Any Server File"

high Symfony Symfony components · Last reviewed Nov 10, 2026

CVE: CVE-2026-121623
GHSA: None
Packagist: PKSA-nyd8-k74r-fsf2
Reported: Nov 4, 2026

Lets a client read any file PHP can read in apps that deserialize client data into SplFileObject, SplFileInfo or File properties.

Affected and fixed versions

In 2 packages: symfony/serializer and symfony/symfony. Find the row for the version you run, and update to the release next to it.

If you run	Update to	Support
8.1.0 – 8.1.10	8.1.11	Supported
7.4.0 – 7.4.22	7.4.23	Supported
6.4.0 – 6.4.49	6.4.50	Supported
5.4.0 – 5.4.55	5.4.56	Supported

Show 16 older branches, no longer supported

8.0.0 – 8.0.x	8.1.11
7.0.0 – 7.0.x	7.4.23
7.1.0 – 7.1.x	7.4.23
7.2.0 – 7.2.x	7.4.23
7.3.0 – 7.3.x	7.4.23
6.0.0 – 6.0.x	6.4.50
6.1.0 – 6.1.x	6.4.50
6.2.0 – 6.2.x	6.4.50
6.3.0 – 6.3.x	6.4.50
2.0.0 – 2.x	5.4.56
3.0.0 – 3.x	5.4.56
4.0.0 – 4.x	5.4.56
5.0.0 – 5.0.x	5.4.56
5.1.0 – 5.1.x	5.4.56
5.2.0 – 5.2.x	5.4.56
5.3.0 – 5.3.x	5.4.56

Upgrade

Run the line for the branch you are on. 1 other package listed above is affected too; update it the same way.

composer require symfony/serializer:^8.1.11
composer require symfony/serializer:^7.4.23
composer require symfony/serializer:^6.4.50
composer require symfony/serializer:^5.4.56

What this means

A client can make your app open any file the PHP process can read, such as .env. The Serializer's DataUriNormalizer accepted data URIs whose scheme wasn't all lowercase, and PHP then opened them as local file paths instead of as data.

Who is affected

Apps that deserialize client data with symfony/serializer (also part of symfony/symfony) into a property typed \SplFileObject, \SplFileInfo or Symfony\Component\HttpFoundation\File\File. FrameworkBundle registers DataUriNormalizer by default. On 6.4 and later, that includes #[MapRequestPayload] DTOs with such a property.

For \SplFileInfo and File, the file is read once your code calls openFile() or getContent(). Apps that never deserialize client data into these types aren't exposed. See the Symfony advisory.

What to do

Update to 5.4.56, 6.4.50, 7.4.23 or 8.1.11. If you're on 8.0, update to 8.1.11. The fix lowercases the scheme before opening the URI, so these values are always read as data.

The same release fixes CVE-2026-118515, which covers properties typed UploadedFile and other subclasses of these classes.

Reported and fixed by Nicolas Grekas.

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 Serializer: Data URIs Can Read Any File on the Server (CVE-2026-121623)
Details: https://phpnews.net/security/symfony/pksa-qsv5-t2f9-c4xk

Affected versions, as Composer constraints:
- symfony/serializer, symfony/symfony: >=2.0.0,<3.0.0|>=3.0.0,<4.0.0|>=4.0.0,<5.0.0|>=5.0.0,<5.1.0|>=5.1.0,<5.2.0|>=5.2.0,<5.3.0|>=5.3.0,<5.4.0|>=5.4.0,<5.4.56|>=6.0.0,<6.1.0|>=6.1.0,<6.2.0|>=6.2.0,<6.3.0|>=6.3.0,<6.4.0|>=6.4.0,<6.4.50|>=7.0.0,<7.1.0|>=7.1.0,<7.2.0|>=7.2.0,<7.3.0|>=7.3.0,<7.4.0|>=7.4.0,<7.4.23|>=8.0.0,<8.1.0|>=8.1.0,<8.1.11

Fixed releases on branches that still get security fixes:
- 8.1.0 – 8.1.10: update to 8.1.11
- 7.4.0 – 7.4.22: update to 7.4.23
- 6.4.0 – 6.4.49: update to 6.4.50
- 5.4.0 – 5.4.55: update to 5.4.56

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/pksa-qsv5-t2f9-c4xk 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

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