CVE-2026-109413
8.7HighPublished 15 Oct 2026 · NVD status: Awaiting Analysis · AI triage by gemini-3.8-flash
- Attack vector
- Network
- Complexity
- Low
- Privileges needed
- None
- User interaction
- None
- Impact
- High impact on availability
- Weakness
- CWE-674
Impact
Remote unauthenticated attackers can crash PHP worker processes and cause denial of service with a single payload. They only need access to an endpoint parsing untrusted YAML, including #[MapRequestPayload] endpoints that accept YAML.
Root cause
The inline collection lexer recurses indefinitely on nested brackets without enforcing the parser's maxNestingLevel limit, causing a stack overflow.
Affected systems
symfony/yaml through 5.4.53, 6.0.0-BETA1 through 6.4.44, 7.0.0-BETA1 through 7.4.17, and 8.0.0-BETA1 through 8.1.5
CVSS v4.0 · CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
Fix & remediation
Upgrade symfony/yaml to 5.4.54, 6.4.45, 7.4.18, or 8.1.6. If you cannot patch immediately, restrict acceptFormat on #[MapRequestPayload] endpoints to reject YAML content types or block YAML input at your reverse proxy.
$ composer update symfony/yamlAI-suggested. Run it in staging first and check it against the vendor advisory. Why?
NVD description
In Symfony YAML prior to versions 5.4.54, 6.4.45, 7.4.18, and 8.1.6, Yaml\Parser::lexInlineStructure() recursed through lexInlineMapping() and lexInlineSequence() for every { and [ of an inline collection, without entering the nesting level that the rest of the parser bounds with maxNestingLevel. A document made of deeply nested inline collections, such as [[[[...]]]], exhausted the stack while it was being lexed: depending on the PHP version and its stack settings, the process crashed or the request ended with a fatal error. Any code parsing untrusted YAML is affected. That includes #[MapRequestPayload] when the Yaml component is installed and the endpoint does not restrict acceptFormat: a single unauthenticated request with a YAML content type is enough. This issue affects symfony/yaml through v5.4.53, v6.0.0-BETA1 through v6.4.44, v7.0.0-BETA1 through v7.4.17, and v8.0.0-BETA1 through v8.1.5.