PT-2026-44149 · Symfony · Symfony

Published 2026-05-21 · Updated 2026-05-27 · CVE-2026-45304

Positive Technologies (AI Summary)

CVSS v4.0

2.7

Low

Base vector

AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N/E:U

Name of the Vulnerable Software and Affected Versions Symfony versions prior to 5.4

Description The SymfonyComponentYamlParser resolves YAML aliases during parsing. Aliases referencing collections, such as arrays, stdClass, or TaggedValue-wrapped collections, can point to other collections containing aliases. This creates exponential expansion during resolution, allowing a small input to expand into a multi-gigabyte structure and exhaust memory. This is a Billion Laughs denial-of-service attack, where a parser is overwhelmed by recursive entity expansion.

Recommendations Update to the patched version of branch 5.4. As a temporary mitigation, use the Yaml::PARSE EXCEPTION ON ALIAS flag to reject all aliases when parsing untrusted input. Restrict the number of collection alias resolutions by configuring the $maxAliasesForCollections argument in Parser:: construct(), Yaml::parse(), or Yaml::parseFile().

Exploit

Fix

XML Entity Expansion

Weakness Enumeration

CWE-776

Related Identifiers

CVE-2026-45304

GHSA-4QPC-3HR4-R2P4

Affected Products

Symfony

References · 13

• 🔥 https://github.com/FriendsOfPHP/security-advisories/blob/master/symfony/yaml/CVE-2026-45304.yaml · Exploit
• 🔥 https://github.com/FriendsOfPHP/security-advisories/blob/master/symfony/symfony/CVE-2026-45304.yaml · Exploit
• https://osv.dev/vulnerability/UBUNTU-CVE-2026-45304 · Vendor Advisory
• https://ubuntu.com/security/CVE-2026-45304 · Vendor Advisory
• https://osv.dev/vulnerability/DEBIAN-CVE-2026-45304 · Vendor Advisory
• https://cve.org/CVERecord?id=CVE-2026-45304 · Security Note
• https://security-tracker.debian.org/tracker/CVE-2026-45304 · Vendor Advisory
• https://osv.dev/vulnerability/GHSA-4qpc-3hr4-r2p4 · Vendor Advisory
• https://github.com/symfony/symfony · Note
• https://github.com/symfony/symfony/commit/e77391b2e4f18821198f010d573674c8ed4a970a · Note
• https://github.com/symfony/symfony/security/advisories/GHSA-4qpc-3hr4-r2p4 · Note
• https://symfony.com/blog/cve-2026-45304-yaml-parser-exponential-memory-allocation-via-recursive-collection-alias-expansion-billion-laughs · Note
• https://symfony.com/cve-2026-45304 · Note