CVE-2026-65636

YAML injection via unescaped newlines in ymlr document comments

Published Jul 31, 2026 CVSS 4.0 · 2.1 Low EPSS < 1% KEV · Not listed
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.

Remediation

Vendor Workaround

Split any untrusted comment string on line breaks and pass the resulting list as the comment element of the {comment, data} tuple. Ymlr prefixes every list element with its own # marker, so no line can leave the comment context. Alternatively, reject comment strings that contain carriage return or line feed characters, or keep untrusted text out of comments entirely and place it in the encoded data instead, where the encoder quotes it.

Tracking

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Advisories

No advisories available
History
Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'no', 'Exploitation': 'poc', 'Technical Impact': 'partial'}, 'version': '2.0.3'}

Type Values Removed Values Added
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.
Title YAML injection via unescaped newlines in ymlr document comments
First Time appeared Ufirstgroup
Ufirstgroup ymlr
Weaknesses CWE-93
CPEs cpe:2.3:a:ufirstgroup:ymlr:*:*:*:*:*:*:*:*
Vendors & Products Ufirstgroup
Ufirstgroup ymlr
References
Metrics cvssV4_0

{'score': 2.1, 'vector': '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'}

Weaknesses

Sources

Status
PUBLISHED
Assigner
EEF
Published
Updated
Aug 1, 2026, 4:18 AM
Reserved
Jul 22, 2026, 1:58 PM
Status
Awaiting Analysis
Published
Jul 31, 2026, 2:16 PM
Modified
Oct 23, 2026, 11:10 PM