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


- **Severity:** High 8.7 (`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`)
- **Exploited in the wild:** Not known
- **Fix available:** Yes
- **Published:** 6 Nov 2026
- **Updated:** 10 Nov 2026
- **Also known as:** DEBIAN-CVE-2026-123792, GHSA-hwfg-qwvh-2wfx, UBUNTU-CVE-2026-123792

## What is CVE-2026-123792?

CVE-2026-123792 is a high-severity vulnerability in sensiolabs symfony, published on 6 Nov 2026. 

### Official 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.

Weakness: CWE-407 (Inefficient Algorithmic Complexity), CWE-1333 (Inefficient Regular Expression Complexity)

## Which versions are affected by CVE-2026-123792?


## How do I fix CVE-2026-123792?

Upgrade to a fixed version.

## Is CVE-2026-123792 being exploited?

There is no known exploitation of CVE-2026-123792 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-123792 and fix it if it is affected.

What it is: CVE-2026-123792 is a high-severity vulnerability in sensiolabs symfony, published on 6 Nov 2026. 
Exploitation: There is no known exploitation of CVE-2026-123792 in the wild and no public exploit code.

Affected product: sensiolabs symfony. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-123792/ (Markdown: https://insights.sbomify.com/CVE-2026-123792/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-123792
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-123792
- OSV: https://osv.dev/vulnerability/CVE-2026-123792

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-123792/
Summaries are generated and may contain mistakes; the official description above is the record.