# CVE-2026-65636: YAML injection via unescaped newlines in ymlr document comments

> Attackers can inject arbitrary YAML content via unescaped newlines in comments, potentially altering configuration or triggering code execution in downstream consumers.

- **Severity:** Low 2.1 (`CVSS:4.0/AV:L/AC:L/AT:P/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:L/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 31 Jul 2026
- **Updated:** 1 Aug 2026
- **Also known as:** EEF-CVE-2026-65636, GHSA-p8qx-7cp9-v6c9

## What is CVE-2026-65636?

CVE-2026-65636 is a low-severity code injection vulnerability in ufirstgroup ymlr, published on 31 Jul 2026. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

Improper Neutralization of CRLF Sequences vulnerability in ufirstgroup ymlr (Elixir.Ymlr module) allows attackers to inject arbitrary content into generated YAML documents through document comments. Ymlr.document!/2 interpolates each caller-supplied comment string into the output behind a single # prefix without validating it or escaping line breaks. Because a YAML comment is terminated by a line break, the first carriage return or line feed in the comment string ends the comment context and everything after it is emitted at column 0 of the document body.

An attacker who controls text that the host application passes as a comment can forge top-level mapping keys, override values the application itself set, and emit --- or ... markers that split the output into additional documents. Downstream consumers of the generated YAML, such as configuration loaders, deployment manifests, CI pipelines and data importers, parse the injected content as legitimate data. The same clause backs Ymlr.document/2, Ymlr.documents!/2 and Ymlr.documents/2, so every document encoding entry point is affected.

This vulnerability is associated with program files lib/ymlr.ex and program routines 'Elixir.Ymlr':document!/2, 'Elixir.Ymlr':documents!/2.

This issue affects ymlr from 0.0.1 before 5.1.6.

Weakness: CWE-93 (Improper Neutralization of CRLF Sequences)

## Which versions are affected by CVE-2026-65636?

1 open source package ship an affected version, including ymlr.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `ymlr` | Hex | From 0.0.1 | 5.1.6 |

## How do I fix CVE-2026-65636?

Upgrade ymlr to 5.1.6 or later.

## Is CVE-2026-65636 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-65636 exists.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-65636 and fix it if it is affected.

What it is: CVE-2026-65636 is a low-severity code injection vulnerability in ufirstgroup ymlr, published on 31 Jul 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-65636 exists.

Affected packages and fixed versions:
- ymlr (Hex): affected from 0.0.1; fixed in 5.1.6

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-2026-65636/ (Markdown: https://insights.sbomify.com/CVE-2026-65636/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-65636
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-65636
- OSV: https://osv.dev/vulnerability/CVE-2026-65636

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-65636/
Summaries are generated and may contain mistakes; the official description above is the record.