CVE-2026-45304

Symfony's YAML Parser Vulnerable to Exponential Memory Allocation via Recursive Collection-Alias Expansion ("Billion Laughs")

發布日:2026/5/27修改日:2026/6/1
也稱為:GHSA-4qpc-3hr4-r2p4DEBIAN-CVE-2026-45304

描述

### Description `Symfony\Component\Yaml\Parser` resolves YAML aliases (`*anchor`) during parsing. Aliases that reference *collections* (arrays, `stdClass`, `TaggedValue`-wrapped collections) can themselves point to other collections containing aliases, creating exponential expansion at resolution time. A small input can blow up into a multi-gigabyte structure and exhaust memory: the classic "Billion Laughs" denial-of-service against any parser exposed to untrusted YAML. ### Resolution The `Parser` now counts collection alias resolutions in a shared `ParserState` object, with a default limit of **128**, following the [SnakeYAML model](https://github.com/snakeyaml/snakeyaml/blob/master/src/main/java/org/yaml/snakeyaml/LoaderOptions.java). Scalar aliases remain unrestricted since they cannot drive exponential growth. The limit is configurable via a new `$maxAliasesForCollections` argument on `Parser::__construct()`, `Yaml::parse()` and `Yaml::parseFile()`. A new `Yaml::PARSE_EXCEPTION_ON_ALIAS` flag also rejects all aliases outright when parsing fully untrusted input. The patch for this issue is available [here](https://github.com/symfony/symfony/commit/e77391b2e4f18821198f010d573674c8ed4a970a) for branch 5.4. ### Credits Symfony would like to thank Pietro Tirenna (Shielder) for reporting the issue and Nicolas Grekas for fixing it.

受影響套件(3)

CVSS 分數

來源版本嚴重程度向量
osvCVSS 4.0—CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N/E:U

參考連結(7)