CVE-2026-54743

MEDIUMPre-NVD 6.46.4
EchelonGraph scoreMEDIUM confidence

“—” beside the score: it is equal to the CVSS score beside it.

This medium-severity CVE scores 6.4 under a secondary CVSS source (NVD's own analysis pending). EPSS exploit probability: 0.5% (44th percentile of EPSS-scored CVEs). No GitHub Security Advisory CVSS is on record for this CVE.

Triggered by: Headline CVSS from a secondary CVSS source
Sources: EPSS, a secondary CVSS source
Elevated
6.4EG
EchelonGraph verdictPlan a fixRemediate within your standard update timelines (the SSVC decision on this page).
  • CISA's Vulnrichment rates exploitation as PoC; EchelonGraph holds no exploit-code reference for it
CISA-KEV: Not listedEPSS PROB: 0.5%CVSS: 6.4Exploit: No code on recordExposed services: Not assessed

The CVE record names the fixed release — apply it.

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 [email protected] 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.

CVSS v3
6.4
EG Score
6.4MEDIUMmedium confidence
EG Risk
45
EG Risk 45/100

EG Risk is EchelonGraph's 0–100 priority score: it fuses intrinsic severity with real-world exploitation and automatability so you can rank equal-severity CVEs and fix the most dangerous first. Higher = act sooner. Distinct from the 0–10 EG Score (severity).

How it’s computed (value × EchelonGraph’s weight)
Severity64% × 45%
The EG Score, 6.4 of 10.
Exploitation40% × 40%
EchelonGraph's fixed weight for EG-KEV Tier 3 (Elevated): a constant, not a probability.
Automatability0% × 15%
CISA's SSVC Automatable value: no (Vulnrichment).
SSVC (CISA's decision table, applied by EchelonGraph): Track at low or medium mission impact; Track* at high (mission-essential systems).
Exploitation public PoC (CISA Vulnrichment) · Automatable no (CISA Vulnrichment) · Technical impact partial (CISA Vulnrichment). All three are CISA's SSVC values (Vulnrichment). EchelonGraph applied CISA's decision table to them; CISA publishes SSVC inputs and the table, not a decision for each CVE.
Action: The CVE record names the fixed release. Apply it within your standard update timelines.
EPSS PROB
0.5%
EPSS %ILE
44th
KEV
Not listed

SSVC (CISA's decision table, applied by EchelonGraph)Track at low or medium mission impact; Track* at high (mission-essential systems).

The CVE record names the fixed release. Apply it within your standard update timelines.

Exploitation public PoC (CISA Vulnrichment) · Automatable no (CISA Vulnrichment) · Technical impact partial (CISA Vulnrichment). All three are CISA's SSVC values (Vulnrichment). EchelonGraph applied CISA's decision table to them; CISA publishes SSVC inputs and the table, not a decision for each CVE. Mission impact is CISA's Mission & Well-being decision point, and only you can judge it. CISA's table makes it high when Mission Prevalence is Essential — the vulnerable component "directly provides capabilities that constitute at least one MEF for at least one entity" (MEF: mission essential function) — or when Public Well-Being Impact is Irreversible: "multiple fatalities are likely", the cyber-physical system "is likely lost or destroyed", "extreme or serious externalities" are imposed on other parties, or social systems such as elections or the financial grid "are destabilized and potentially collapse". CISA's decision table

BOD 26-04 (CISA's remediation timeline, Table 1)60 days if the affected system is publicly exposed; Fix on system upgrade if it is not.

In CISA KEV no (CISA's KEV catalog) · Automatable no (CISA Vulnrichment) · Technical impact partial (CISA Vulnrichment). Whether your system is publicly exposed is yours to answer. BOD 26-04 binds US Federal Civilian Executive Branch agencies; for anyone else it is CISA's published timeline, a reference rather than an obligation. The directive · how EchelonGraph applies it

Published

August 19, 2026

Last Modified

September 9, 2026

Advisory Details (3)

Auto-updated Aug 19, 2026
Fix named in the CVE record. Sources: github, github_pr, github_commit.
GitHub commit

commit 81a3fe07f2a5 (LemmyNet/lemmy-ui)

Fix landed in LemmyNet/lemmy-ui commit 81a3fe07f2a5 — awaiting tagged release

https://github.com/LemmyNet/lemmy-ui/commit/81a3fe07f2a5acc11188320534aa6bf937ebf7ff
GitHub pull request

[0.19] Swap library for markdown media embeds

Fix merged in LemmyNet/lemmy-ui PR #4213 on 2026-06-03 — awaiting tagged release

https://github.com/LemmyNet/lemmy-ui/pull/4213
GitHub advisoryMentions a patch (unverified)

Stored XSS via markdown image alt-text in lemmy-ui html5-embed · Advisory · LemmyNet/lemmy · GitHub

https://github.com/LemmyNet/lemmy/security/advisories/GHSA-2g66-9fr3-ppwj

Weakness Classification(1)

MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.

Data Freshness Timeline

(refreshed 12× in last 7d / 52× in last 30d)

Each row is a time one of our pipelines fetched, updated or re-scored this CVE. For example, "NVD update" means NVD published or revised its analysis for this CVE; "MITRE cvelistV5" means we ingested or refreshed it from the CNA feed. An arrow marks a change the record states ("CVSS v3 → 9.1"); EPSS and GHSA rows show the values recorded at that time, not what changed (EPSS values are rounded; hover one for the exact figures). Most recent first.

  1. 2026-10-13 16:34 UTCEPSS rescoreEPSS 0.5% · 44th percentile
  2. 2026-10-12 16:34 UTCEPSS rescoreEPSS 0.5% · 44th percentile
  3. 2026-10-12 15:56 UTCEG score recompute
  4. 2026-10-11 19:39 UTCEG score recompute
  5. 2026-10-11 16:54 UTCEG score recompute
  6. 2026-10-11 14:17 UTCEG score recompute
  7. 2026-10-11 13:49 UTCEPSS rescoreEPSS 0.5% · 44th percentile
  8. 2026-10-10 20:00 UTCEPSS rescoreEPSS 0.5% · 44th percentile
  9. 2026-10-09 20:07 UTCEPSS rescoreEPSS 0.5% · 44th percentile
  10. 2026-10-08 17:12 UTCEPSS rescoreEPSS 0.5% · 44th percentile
  11. 2026-10-08 06:36 UTCEG score recompute
  12. 2026-10-07 23:48 UTCEPSS rescoreEPSS 0.5% · 44th percentile
  13. 2026-10-07 06:37 UTCEG score recompute
  14. 2026-10-06 15:18 UTCEPSS rescoreEPSS 0.5% · 44th percentile
  15. 2026-10-06 07:55 UTCEG score recompute
  16. 2026-10-05 17:43 UTCEPSS rescoreEPSS 0.5% · 43rd percentile
  17. 2026-10-05 05:07 UTCEG score recompute
  18. 2026-10-04 23:22 UTCEPSS rescoreEPSS 0.5% · 43rd percentile
  19. 2026-10-04 04:10 UTCEG score recompute
  20. 2026-10-03 14:26 UTCEPSS rescoreEPSS 0.5% · 43rd percentile
  21. 2026-10-03 05:31 UTCEG score recompute
  22. 2026-10-02 17:56 UTCEPSS rescoreEPSS 0.5% · 43rd percentile
  23. 2026-10-02 06:50 UTCEG score recompute
  24. 2026-10-01 19:50 UTCEPSS rescoreEPSS 0.5% · 43rd percentile
  25. 2026-10-01 07:17 UTCEG score recompute
Show 72 more
  1. 2026-09-30 15:03 UTCEPSS rescoreEPSS 0.5% · 43rd percentile
  2. 2026-09-30 08:37 UTCEG score recompute
  3. 2026-09-29 15:22 UTCEPSS rescoreEPSS 0.5% · 43rd percentile
  4. 2026-09-29 03:20 UTCEG score recompute
  5. 2026-09-28 13:51 UTCEPSS rescoreEPSS 0.5% · 43rd percentile
  6. 2026-09-28 04:39 UTCEG score recompute
  7. 2026-09-27 13:48 UTCEPSS rescoreEPSS 0.5% · 43rd percentile
  8. 2026-09-27 05:57 UTCEG score recompute
  9. 2026-09-26 15:59 UTCEPSS rescoreEPSS 0.5% · 43rd percentile
  10. 2026-09-25 02:48 UTCEG score recompute
  11. 2026-09-24 14:04 UTCEPSS rescoreEPSS 0.5% · 43rd percentile
  12. 2026-09-24 04:08 UTCEG score recompute
  13. 2026-09-23 17:54 UTCEPSS rescoreEPSS 0.5% · 42nd percentile
  14. 2026-09-23 05:26 UTCEG score recompute
  15. 2026-09-22 06:47 UTCEG score recompute
  16. 2026-09-21 08:06 UTCEG score recompute
  17. 2026-09-20 20:16 UTCEPSS rescoreEPSS 0.5% · 42nd percentile
  18. 2026-09-20 09:26 UTCEG score recompute
  19. 2026-09-19 10:46 UTCEG score recompute
  20. 2026-09-18 19:28 UTCEPSS rescoreEPSS 0.5% · 42nd percentile
  21. 2026-09-18 11:52 UTCEG score recompute
  22. 2026-09-17 19:31 UTCEPSS rescoreEPSS 0.5% · 42nd percentile
  23. 2026-09-16 14:32 UTCEG score recompute
  24. 2026-09-16 14:08 UTCEPSS rescoreEPSS 0.5% · 42nd percentile
  25. 2026-09-16 05:15 UTCEPSS rescoreEPSS 0.5% · 42nd percentile
  26. 2026-09-15 15:14 UTCEG score recompute
  27. 2026-09-15 03:11 UTCEPSS rescoreEPSS 0.5% · 41st percentile
  28. 2026-09-13 17:36 UTCEG score recompute
  29. 2026-09-13 16:47 UTCEPSS rescoreEPSS 0.5% · 41st percentile
  30. 2026-09-12 18:56 UTCEG score recompute
  31. 2026-09-11 20:16 UTCEG score recompute
  32. 2026-09-11 14:53 UTCEPSS rescoreEPSS 0.5% · 41st percentile
  33. 2026-09-10 21:15 UTCEG score recompute
  34. 2026-09-10 09:35 UTCEPSS rescoreEPSS 0.4% · 33rd percentile
  35. 2026-09-09 02:29 UTCEG score recompute
  36. 2026-09-08 22:01 UTCEPSS rescoreEPSS 0.4% · 33rd percentile
  37. 2026-09-07 19:54 UTCEG score recompute
  38. 2026-09-07 16:01 UTCEPSS rescoreEPSS 0.4% · 33rd percentile
  39. 2026-09-06 21:14 UTCEG score recompute
  40. 2026-09-06 13:47 UTCEPSS rescoreEPSS 0.4% · 33rd percentile
  41. 2026-09-05 22:34 UTCEG score recompute
  42. 2026-09-04 23:54 UTCEG score recompute
  43. 2026-09-04 05:06 UTCEPSS rescoreEPSS 0.4% · 33rd percentile
  44. 2026-09-03 02:26 UTCEG score recompute
  45. 2026-09-02 14:12 UTCEPSS rescoreEPSS 0.4% · 33rd percentile
  46. 2026-09-02 03:45 UTCEG score recompute
  47. 2026-09-01 13:54 UTCEPSS rescoreEPSS 0.4% · 33rd percentile
  48. 2026-09-01 05:04 UTCEG score recompute
  49. 2026-09-01 04:40 UTCEPSS rescoreEPSS 0.4% · 33rd percentile
  50. 2026-08-31 06:19 UTCEG score recompute
  51. 2026-08-30 19:17 UTCEPSS rescoreEPSS 0.4% · 33rd percentile
  52. 2026-08-30 07:32 UTCEG score recompute
  53. 2026-08-30 01:22 UTCEPSS rescoreEPSS 0.4% · 33rd percentile
  54. 2026-08-29 08:52 UTCEG score recompute
  55. 2026-08-28 21:41 UTCEPSS rescoreEPSS 0.4% · 33rd percentile
  56. 2026-08-28 10:11 UTCEG score recompute
  57. 2026-08-27 14:25 UTCEPSS rescoreEPSS 0.4% · 33rd percentile
  58. 2026-08-27 11:31 UTCEG score recompute
  59. 2026-08-26 14:46 UTCEPSS rescoreEPSS 0.4% · 33rd percentile
  60. 2026-08-25 14:11 UTCEG score recompute
  61. 2026-08-25 13:49 UTCEPSS rescoreEPSS 0.4% · 32nd percentile
  62. 2026-08-24 15:26 UTCEG score recompute
  63. 2026-08-23 16:44 UTCEG score recompute
  64. 2026-08-23 00:19 UTCEPSS rescoreEPSS 0.4% · 33rd percentile
  65. 2026-08-22 18:04 UTCEG score recompute
  66. 2026-08-21 23:49 UTCEPSS rescoreEPSS 0.4% · 33rd percentile
  67. 2026-08-21 19:24 UTCEG score recompute
  68. 2026-08-21 18:30 UTCEG score recompute
  69. 2026-08-20 22:55 UTCEPSS rescoreEPSS 0.4% · 33rd percentile
  70. 2026-08-19 21:19 UTCEG score recompute
  71. 2026-08-19 20:28 UTCEG score recomputeFirst assessed: 6.4 MEDIUM
  72. 2026-08-19 20:27 UTCMITRE cvelistV5first tracked

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Frequently asked(5)

What is CVE-2026-54743?
CVE-2026-54743 is a medium-severity vulnerability; its CVE record was published on August 19, 2026. 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…
When was the CVE record for CVE-2026-54743 published?
The CVE record for CVE-2026-54743 was published on August 19, 2026. That is the record's publication date; the vulnerability itself may have been made public earlier. EchelonGraph's copy of the record carries a last-modified date of September 9, 2026; the record at its source may have been updated since.
Is CVE-2026-54743 actively exploited?
CVE-2026-54743 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 0.5% probability of exploitation in the next 30 days (44th percentile of EPSS-scored CVEs).
What is the CVSS score of CVE-2026-54743?
CVE-2026-54743 has a CVSS base score of 6.4 (a secondary CVSS source that NVD displays; NVD's own analysis pending).
How do I remediate CVE-2026-54743?
The CVE record for CVE-2026-54743 names the fix: "This issue is fixed in lemmy-ui version 0.19.19-beta.1."

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