Lemmy: Stored XSS via markdown image alt-text in lemmy-ui html5-embed
Default status is the baseline for the product, each version can override it (e.g. patched versions marked unaffected).
| Vendor | Product | Default status | Versions | ||||||
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| LemmyNet | lemmy | affected |
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No data.
No data.
| Vendor | Product | Versions | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|
| Lemmynet | Lemmy |
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No CVSS v3.1
No CVSS v3.0
No CVSS v2
This CVE is not in the KEV list.
Exploit prediction score: < 1% (0.547% probability within 30 days)
| Type | Values Removed | Values Added |
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| Metrics |
ssvc
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| Type | Values Removed | Values Added |
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| First Time appeared |
Lemmynet
Lemmynet lemmy |
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| Vendors & Products |
Lemmynet
Lemmynet lemmy |
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| Description | Lemmy is a link aggregator and forum for the fediverse. Prior to lemmy-ui 0.19.19-beta.1, LemmyNet/lemmy-ui renders Markdown in src/shared/markdown.ts for post bodies, comment bodies, private messages, and community and site sidebars through mdToHtml, which returns a raw __html object that Inferno injects without a sanitizer pass. setupMarkdown configures html as false but registers markdown-it-html5-embed@1.0.0 with useImageSyntax enabled, so an image targeting video media becomes a video element whose fallback incorporates the image alt text through unescaped string replacement. The html setting does not apply to plugin-generated output, allowing crafted alt text to reach the DOM as live HTML in contexts that do not use mdToHtmlNoImages. An approved member or a remote federated instance can store such content, and a viewer who renders it may execute JavaScript in the lemmy-ui origin, exposing the viewer's session and authenticated actions. The advisory notes that Content Security Policy prevents the described exploit in production, but also states that the tested default self-hosted deployment serves no Content-Security-Policy. This issue is fixed in lemmy-ui version 0.19.19-beta.1. | |
| Title | Lemmy: Stored XSS via markdown image alt-text in lemmy-ui html5-embed | |
| Weaknesses | CWE-79 | |
| References |
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| Metrics |
cvssV4_0
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