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CVE-2026-123792— Symfony: Exponential and Quadratic Parse Times in the YAML Parser Let a Single Document Hold a Process

Quick assessment

Affected
sensiolabs symfony
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

Symfony Yaml 组件中的 和 模块在解析某些 YAML 文档时效率低下，导致一个精心构造的小型文档需要耗费不成比例的时间进行处理。这会使 PHP 进程持续繁忙数秒甚至数分钟，从而在以下版本的 Symfony 中引发拒绝服务（DoS）风险： 5.4 系列：5.4.56 之前的版本 6.x 系列：6.4.50 之前的版本 7.x 系列：7.4.23 之前的版本 8.x 系列：8.1.11 之前的版本 该解析器在多个位置重复执行已完成的计算工作。具体表现为： 1. 指数级时间增长：流序列（flow sequen

CVSS 8.7 · High

Possible ATT&CK Techniques 1 AI

T1190 · Exploit Public-Facing Application
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I. Basic Information for CVE-2026-123792

Vulnerability Information
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Vulnerability Title
Symfony: Exponential and Quadratic Parse Times in the YAML Parser Let a Single Document Hold a Process
Source: CVE Program / CVE List V5
Vulnerability Description
The 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.
Source: CVE Program / CVE List V5
CVSS Information
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
Source: CVE Program / CVE List V5
Vulnerability Type
算法复杂性
Source: CVE Program / CVE List V5

Affected Products

Vendor Product Affected Versions CPE Subscribe
sensiolabs symfony 0 ~ 5.4.56 -

II. Public POCs for CVE-2026-123792

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III. Intelligence Information for CVE-2026-123792

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Other References for CVE-2026-123792 (4)

Same Patch Batch · sensiolabs · 2026-11-06 · 7 CVEs total

CVE-2026-118515 8.4 HIGH Symfony: The Serializer Builds UploadedFile Objects From Request Data, Letting a Client Po
CVE-2026-121623 8.2 HIGH Symfony: DataUriNormalizer Opens Data URIs With a Non-Lowercase Scheme as Local Files, Let
CVE-2026-122053 6.9 MEDIUM Symfony: ObjectNormalizer Dotted-Key Property-Path Traversal Bypasses #[Ignore] on Nested
CVE-2026-123746 2.3 LOW Symfony: Programmatic Logins Skip the checkPostAuth() Method of User Checkers
CVE-2026-123339 2.3 LOW Symfony: Inline Fragments Let Untrusted Forwarded Headers Set the Host, Scheme and Port of
CVE-2026-123824 2.3 LOW Symfony: XXE (Local File Read) in Config XmlUtils::parse() via validateOnParse = true

IV. Related Vulnerabilities

Same product: symfony
Same vendor: sensiolabs
Same weakness: CWE-407