Symfony: Exponential and Quadratic Parse Times in the YAML Parser Let a Single Document Hold a Process

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-123792
StatePUBLISHED
AssignerCheckmarx
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-11-06 16:17:55 UTC
Updated2026-11-06 21:40:43 UTC
DescriptionThe Symfony Yaml components Inline and Parser, parse some YAML documents inefficiently, so that a small crafted document can take disproportionately long to process, keeping a PHP process busy for seconds or minutes, potentially causing a denial of service in Symfony versions prior to 5.4.56, 6.x prior to 6.4.50, 7.x prior to 7.4.23, and 8.x prior to 8.1.11. The parser repeats work it has already done in several places. An embedded mapping in a flow sequence is parsed again for every scalar appended to it, and so are the collections nested in it, so the parse time grows exponentially with the nesting depth. The patterns matching mapping keys and tags scan a run of spaces once per character of the run, and each scalar of a flow collection is matched against a copy of the rest of the collection, so the parse time grows quadratically with the size of the input. Nested blocks are also copied at each nesting level, which consumes memory as well as time. A few other constructs, such as an empty sequence item followed by a blank line or an anchor named 0, trigger similar repeated work. Any code parsing untrusted YAML is affected, with the default flags. In Symfony 7.4 and later, 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 keeps a PHP worker busy until max_execution_time. JSON documents are valid YAML, so a JSON payload sent with a YAML content type is enough for the flow collection case. In Symfony 6.4, #[MapRequestPayload] accepts YAML only when the application registers a yaml request format.

Risk And Classification

Primary CVSS: v4.0 8.7 HIGH from 596c5446-0ce5-4ba2-aa66-48b3b757a647

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

EPSS: 0.005040000 probability, percentile 0.433460000 (date 2026-11-07)

Problem Types: CWE-407 | CWE-1333 | CWE-407 CWE-407 Inefficient Algorithmic Complexity | CWE-1333 CWE-1333 Inefficient regular expression complexity

VersionSourceTypeScoreSeverityVector
4.0596c5446-0ce5-4ba2-aa66-48b3b757a647Secondary8.7HIGHCVSS: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/C...
4.0CNACVSS8.7HIGHCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N

CVSS v4.0 Breakdown

Attack Vector
Network
Attack Complexity
Low
Attack Requirements
None
Privileges Required
None
User Interaction
None
Confidentiality
None
Integrity
None
Availability
High
Sub Conf.
None
Sub Integrity
None
Sub Availability
None

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

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Sensiolabs Symfony affected 5.4.56 git Not specified
CNA Sensiolabs Symfony affected 6.0.0 6.4.50 git Not specified
CNA Sensiolabs Symfony affected 7.0.0 7.4.23 git Not specified
CNA Sensiolabs Symfony affected 8.0.0 8.1.11 git Not specified

References

ReferenceSourceLinkTags
github.com/symfony/symfony/commit/08db22d52e5d3e6ec2f5c50db30a4d818100ffb9 596c5446-0ce5-4ba2-aa66-48b3b757a647 github.com
github.com/symfony/symfony/security/advisories/GHSA-hwfg-qwvh-2wfx 596c5446-0ce5-4ba2-aa66-48b3b757a647 github.com
github.com/symfony/symfony/commit/487f63bf2cacebc8ed8273c5c10d92955acd2402 596c5446-0ce5-4ba2-aa66-48b3b757a647 github.com
github.com/symfony/symfony/commit/49e03035eda3000e978a4612db74900013255ccd 596c5446-0ce5-4ba2-aa66-48b3b757a647 github.com
CVE Program record CVE.ORG www.cve.org canonical
NVD vulnerability detail NVD nvd.nist.gov canonical, analysis

Vendor Comments And Credit

Discovery Credit

CNA: Sebastian Bergmann (en)

CNA: Nicolas Grekas (en)

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