CVE-2026-45133

Description

### Description `Symfony\Component\Yaml\Parser` is the entry point for parsing YAML strings into PHP values via `Yaml::parse()`. When the parser is exposed to attacker-controlled input, deeply nested mappings or sequences cause both the block-level (`Parser::parseBlock()`) and inline (`Inline::parseSequence()` / `Inline::parseMapping()`) parsers to recurse without a depth limit. A crafted document exhausts the PHP stack and crashes the worker. ### Resolution The `Parser` now tracks recursion depth in a shared `ParserState` object across both block-level and inline parsing, with a default limit of **128**. The limit is configurable via a new `$maxNestingLevel` argument on `Parser::__construct()`, `Yaml::parse()` and `Yaml::parseFile()`. The patch for this issue is available [here](https://github.com/symfony/symfony/commit/914f427ed9630ddb3904dafba763e53d9f133fe3) for branch 5.4. ### Credits Symfony would like to thank Pietro Tirenna (Shielder) for reporting the issue and Nicolas Grekas for fixing it.

How to fix CVE-2026-45133

To remediate CVE-2026-45133, upgrade the affected package to a fixed version below.

• —no fix listed
• —upgrade to 5.4.52 or later
• —upgrade to 5.4.52 or later

Is CVE-2026-45133 being exploited?

No exploitation signal available. Neither CISA KEV nor a current EPSS score has been published for CVE-2026-45133.

Affected packages (3)

• from 0
• from 0, < 5.4.52
• from 0, < 5.4.52

CVSS scores

References (7)

• ADVISORYsecurity-tracker.debian.org/tracker/CVE-2026-45133
• PATCHgithub.com/symfony/symfony
• WEBgithub.com/FriendsOfPHP/security-advisories/blob/master/symfony/symfony/CVE-2026-45133.yaml
• WEBgithub.com/FriendsOfPHP/security-advisories/blob/master/symfony/yaml/CVE-2026-45133.yaml