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.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
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
Which versions are affected by CVE-2026-65636?
1 open source package ship an affected version, including ymlr.
| Package | 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.
Upgrade, and never evaluate templates, expressions or code built from user input. More about Code injection.
Is CVE-2026-65636 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-65636 exists.
Sources
Also known as EEF-CVE-2026-65636, GHSA-p8qx-7cp9-v6c9.