CVE-2026-54743Network attack vectorHinoki check available

Stored XSS via markdown alt-text

Published Aug 19, 2026 · Updated Aug 19, 2026

Stored XSS in LemmyNet lemmy-ui before 0.19.19-beta.1 allows remote authenticated users to execute JavaScript via crafted Markdown. In src/shared/markdown.ts, mdToHtml returns raw __html for Inferno, while setupMarkdown enables markdown-it-html5-embed to turn image syntax for video media into fallback HTML that inserts the image alt text with unescaped string replacement. An approved member or a remote federated instance can plant the payload, and exploitation requires a viewer to render the content where Content Security Policy is absent, as in the advisory's default self-hosted lemmy-ui deployment.

CVSS severity6.4
Medium
EPSS probability0.51%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkAvailable
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Summary

What happened

Stored XSS in LemmyNet lemmy-ui before 0.19.19-beta.1 allows remote authenticated users to execute JavaScript via crafted Markdown. In src/shared/markdown.ts, mdToHtml returns raw __html for Inferno, while setupMarkdown enables markdown-it-html5-embed to turn image syntax for video media into fallback HTML that inserts the image alt text with unescaped string replacement. An approved member or a remote federated instance can plant the payload, and exploitation requires a viewer to render the content where Content Security Policy is absent, as in the advisory's default self-hosted lemmy-ui deployment.

The record

CVE
CVE-2026-54743
Published
Aug 19, 2026
Updated
Aug 19, 2026
Vendor
LemmyNet
Product
Lemmy
Classifications
CWE-79, T1189
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Aug 19, 2026CVE publishedPublication date reported by the CVE source.
  2. Aug 19, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=< 0.19.19-beta.1

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

LemmyNet · Lemmyversion=< 0.19.19-beta.1

Published CVSS scores

6.4GitHub, Inc.CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:N/VI:N/VA:N/SC:H/SI:H/SA:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-79Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
T1189Drive-by Compromise

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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