CVE-2023-36459

CRITICALNVD 9.39.3
EchelonGraph scoreMEDIUM confidence

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

This critical-severity CVE scores 9.3 under NVD CVSS v3. EPSS exploit probability: 1.2% (68th percentile of EPSS-scored CVEs). No GitHub Security Advisory CVSS is on record for this CVE.

Triggered by: Headline CVSS from NVD CVSS v3
Sources: EPSS, NVD CVSS v3
9.3EG
EchelonGraph verdictPlan a fixRemediate within your standard update timelines (the SSVC decision on this page).
  • High severity, but no confirmed exploitation yet
CISA-KEV: Not listedEPSS PROB: 1.2%CVSS: 9.3Exploit: None knownExposed services: Not assessed

A fix is available — apply it.

Mastodon is a free, open-source social network server based on ActivityPub. Starting in version 1.3 and prior to versions 3.5.9, 4.0.5, and 4.1.3, an attacker using carefully crafted oEmbed data can bypass the HTML sanitization performed by Mastodon and include arbitrary HTML in oEmbed preview cards. This introduces a vector for cross-site scripting (XSS) payloads that can be rendered in the user's browser when a preview card for a malicious link is clicked through. Versions 3.5.9, 4.0.5, and 4.1.3 contain a patch for this issue.

CVSS v3
9.3
EG Score
9.3CRITICALmedium confidence
EG Risk
42
EG Risk 42/100

EG Risk is EchelonGraph's 0–100 priority score. It fuses impact severity (EG Severity, the CVSS base score, never the KEV-floored or EPSS-lifted EG Score) with real-world exploitation and automatability, under weights EchelonGraph set by hand, so you can rank equal-severity CVEs and fix the most dangerous first. Higher = act sooner.

How it’s computed (value × EchelonGraph’s weight)
Severity93% × 45%
Impact severity (EG Severity): CVSS 9.3 of 10. Never the KEV-floored or EPSS-lifted EG Score.
Exploitation1.2% × 40%
FIRST EPSS: the 30-day exploitation probability when EchelonGraph scored this CVE.
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 none (CISA Vulnrichment) · Automatable no (CISA Vulnrichment) · Technical impact total (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: A fix is available. Apply it within your standard update timelines.
EPSS PROB
1.2%
EPSS %ILE
68th
KEV
Not listed

What the EG score is made of (scorer v4.0: the three questions the 0–10 score mixes, published apart · methodology)

The EG score (9.3): severity, escalated by confirmed exploitation. This CVE's 9.3 is its impact severity (EG Severity), not escalated.

EG Severity
9.3 CRITICALCVSS-B, impact only: no KEV listing, EPSS or EG-KEV tier raises it.NVD CVSS v3 · CVSS v3.0 or v3.1
EG Likelihood
1.2% within 30 daysSource: FIRST EPSS (model v2026.06.15, score date 2026-10-22). FIRST's exploitation probability, not an EchelonGraph model.
Confirmed exploitation
None on record (CISA KEV, EG-KEV Tier 1)Reported apart from the likelihood: an observed fact, not a probability.
EG Priority
SSVC Track at medium mission impactTrack at low or medium mission impact; Track* at high (mission-essential systems).CISA BOD 26-04: 14 days if the affected system is publicly exposed; Fix on system upgrade if it is not.Each input and its source: the SSVC and BOD 26-04 blocks below.

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

A fix is available. Apply it within your standard update timelines.

Exploitation none (CISA Vulnrichment) · Automatable no (CISA Vulnrichment) · Technical impact total (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)14 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 total (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

July 6, 2023

Last Modified

November 21, 2024

Advisory Details (6)

Auto-updated Sep 15, 2026
Patch available. Sources: github, github_commit, github_release.
GitHub release Patch Available

v4.0.5

Patch available: mastodon/mastodon v4.0.5

https://github.com/mastodon/mastodon/releases/tag/v4.0.5
GitHub release Patch Available

v3.5.9

Patch available: mastodon/mastodon v3.5.9

https://github.com/mastodon/mastodon/releases/tag/v3.5.9
GitHub commit

commit 6d8e0fae3e96 (mastodon/mastodon)

Fix landed in mastodon/mastodon commit 6d8e0fae3e96 — awaiting tagged release

https://github.com/mastodon/mastodon/commit/6d8e0fae3e96f3cf4febe03fa7fcf5b95ff761b2
Web page

oss-security - CVE-2023-36459: mastodon: XSS through oEmbed preview cards

http://www.openwall.com/lists/oss-security/2023/07/06/5
GitHub advisoryMentions a patch (unverified)

XSS through oEmbed preview cards · Advisory · mastodon/mastodon · GitHub

https://github.com/mastodon/mastodon/security/advisories/GHSA-ccm4-vgcc-73hp
GitHub release Patch Available

v4.1.3

Patch available: mastodon/mastodon v4.1.3

https://github.com/mastodon/mastodon/releases/tag/v4.1.3

Weakness Classification(1)

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

Data Freshness Timeline

(refreshed 13× in last 7d / 40× 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.

Showing the most recent 96 of 205 refreshes on record for this CVE.

A repeat, a row identical to one the same pipeline wrote less than 10 seconds earlier, is not a separate refresh and is not counted. 4 repeat rows among the latest 100 are merged into the row they repeat. The 109 oldest rows on record are not shown and were not checked, so the counts can still include repeats.

  1. 2026-10-23 16:29 UTCEPSS rescoreEPSS 1.2% · 68th percentile
  2. 2026-10-23 08:29 UTCEG score recompute
  3. 2026-10-22 16:31 UTCEPSS rescoreEPSS 1.2% · 68th percentile
  4. 2026-10-22 07:37 UTCEG score recompute
  5. 2026-10-21 16:29 UTCEPSS rescoreEPSS 1.2% · 68th percentile
  6. 2026-10-21 06:43 UTCEG score recompute
  7. 2026-10-20 16:29 UTCEPSS rescoreEPSS 1.2% · 68th percentile
  8. 2026-10-20 05:52 UTCEG score recompute
  9. 2026-10-19 16:29 UTCEPSS rescoreEPSS 1.2% · 68th percentile
  10. 2026-10-19 04:58 UTCEG score recompute
  11. 2026-10-18 04:06 UTCEG score recompute
  12. 2026-10-17 16:29 UTCEPSS rescoreEPSS 1.2% · 68th percentile
  13. 2026-10-17 03:11 UTCEG score recompute
  14. 2026-10-16 16:35 UTCEPSS rescoreEPSS 1.2% · 68th percentile
  15. 2026-10-16 02:17 UTCEG score recompute
  16. 2026-10-15 16:29 UTCEPSS rescoreEPSS 1.2% · 68th percentile
  17. 2026-10-14 22:13 UTCEG score recompute
  18. 2026-10-14 16:29 UTCEPSS rescoreEPSS 1.2% · 68th percentile
  19. 2026-10-13 17:52 UTCEG score recompute
  20. 2026-10-13 16:30 UTCEPSS rescoreEPSS 1.2% · 67th percentile
  21. 2026-10-12 16:59 UTCEG score recompute
  22. 2026-10-12 16:30 UTCEPSS rescoreEPSS 1.2% · 67th percentile
  23. 2026-10-11 21:50 UTCEG score recompute
  24. 2026-10-11 13:45 UTCEPSS rescoreEPSS 1.2% · 67th percentile
  25. 2026-10-10 19:57 UTCEPSS rescoreEPSS 1.2% · 67th percentile
Show 71 more
  1. 2026-10-09 20:05 UTCEPSS rescoreEPSS 1.2% · 67th percentile
  2. 2026-10-08 17:06 UTCEPSS rescoreEPSS 1.2% · 67th percentile
  3. 2026-10-07 23:46 UTCEPSS rescoreEPSS 1.2% · 67th percentile
  4. 2026-10-06 15:15 UTCEPSS rescoreEPSS 1.2% · 67th percentile
  5. 2026-10-05 17:41 UTCEPSS rescoreEPSS 1.2% · 67th percentile
  6. 2026-10-04 23:20 UTCEPSS rescoreEPSS 1.2% · 67th percentile
  7. 2026-10-03 14:23 UTCEPSS rescoreEPSS 1.2% · 67th percentile
  8. 2026-09-30 16:26 UTCEG score recompute
  9. 2026-09-30 15:01 UTCEPSS rescoreEPSS 1.2% · 67th percentile
  10. 2026-09-29 15:16 UTCEPSS rescoreEPSS 1.2% · 67th percentile
  11. 2026-09-28 13:49 UTCEPSS rescoreEPSS 1.2% · 67th percentile
  12. 2026-09-27 13:42 UTCEPSS rescoreEPSS 1.2% · 67th percentile
  13. 2026-09-26 15:55 UTCEPSS rescoreEPSS 1.2% · 67th percentile
  14. 2026-09-26 00:22 UTCEPSS rescoreEPSS 1.2% · 67th percentile
  15. 2026-09-24 14:01 UTCEPSS rescoreEPSS 1.2% · 67th percentile
  16. 2026-09-23 13:45 UTCEPSS rescoreEPSS 1.2% · 67th percentile
  17. 2026-09-23 06:15 UTCOSV refresh
  18. 2026-09-22 14:45 UTCEPSS rescoreEPSS 1.2% · 67th percentile
  19. 2026-09-16 14:05 UTCEPSS rescoreEPSS 1.2% · 67th percentile
  20. 2026-09-13 16:44 UTCEPSS rescoreEPSS 1.2% · 66th percentile
  21. 2026-09-12 14:58 UTCEPSS rescoreEPSS 1.2% · 66th percentile
  22. 2026-09-11 14:50 UTCEPSS rescoreEPSS 1.2% · 66th percentile
  23. 2026-09-11 09:34 UTCEPSS rescoreEPSS 1.2% · 66th percentile
  24. 2026-09-08 21:57 UTCEPSS rescoreEPSS 1.2% · 66th percentile
  25. 2026-09-07 15:59 UTCEPSS rescoreEPSS 1.2% · 66th percentile
  26. 2026-09-06 13:45 UTCEPSS rescoreEPSS 1.2% · 66th percentile
  27. 2026-09-05 15:26 UTCEPSS rescoreEPSS 1.2% · 66th percentile
  28. 2026-09-04 13:58 UTCEPSS rescoreEPSS 1.2% · 66th percentile
  29. 2026-09-04 05:04 UTCEPSS rescoreEPSS 1.2% · 66th percentile
  30. 2026-09-04 00:59 UTCOSV refresh
  31. 2026-09-02 14:09 UTCEPSS rescoreEPSS 1.2% · 66th percentile
  32. 2026-09-01 13:51 UTCEPSS rescoreEPSS 1.2% · 66th percentile
  33. 2026-08-30 19:15 UTCEPSS rescoreEPSS 1.2% · 66th percentile
  34. 2026-08-30 01:20 UTCEPSS rescoreEPSS 1.2% · 65th percentile
  35. 2026-08-28 21:38 UTCEPSS rescoreEPSS 1.2% · 65th percentile
  36. 2026-08-27 14:23 UTCEPSS rescoreEPSS 1.2% · 66th percentile
  37. 2026-08-26 14:43 UTCEPSS rescoreEPSS 1.2% · 66th percentile
  38. 2026-08-25 13:46 UTCEPSS rescoreEPSS 1.2% · 66th percentile
  39. 2026-08-24 14:14 UTCEPSS rescoreEPSS 1.2% · 66th percentile
  40. 2026-08-23 00:17 UTCEPSS rescoreEPSS 1.2% · 66th percentile
  41. 2026-08-21 23:47 UTCEPSS rescoreEPSS 1.2% · 66th percentile
  42. 2026-08-20 22:53 UTCEPSS rescoreEPSS 1.2% · 66th percentile
  43. 2026-08-19 17:02 UTCEPSS rescoreEPSS 1.2% · 66th percentile
  44. 2026-08-18 13:46 UTCEPSS rescoreEPSS 1.2% · 66th percentile
  45. 2026-08-17 13:45 UTCEPSS rescoreEPSS 1.2% · 66th percentile
  46. 2026-08-17 13:36 UTCOSV refresh
  47. 2026-08-16 14:54 UTCEPSS rescoreEPSS 1.2% · 66th percentile
  48. 2026-08-16 02:12 UTCEPSS rescoreEPSS 1.2% · 66th percentile
  49. 2026-08-15 01:28 UTCEPSS rescoreEPSS 1.2% · 65th percentile
  50. 2026-08-13 21:58 UTCEPSS rescoreEPSS 1.2% · 65th percentile
  51. 2026-08-12 13:48 UTCEPSS rescoreEPSS 1.2% · 65th percentile
  52. 2026-08-11 13:39 UTCEPSS rescoreEPSS 1.2% · 65th percentile
  53. 2026-08-09 13:44 UTCEPSS rescoreEPSS 1.2% · 65th percentile
  54. 2026-08-08 16:34 UTCEPSS rescoreEPSS 1.2% · 65th percentile
  55. 2026-08-07 16:24 UTCEPSS rescoreEPSS 1.2% · 65th percentile
  56. 2026-08-06 13:44 UTCEPSS rescoreEPSS 1.2% · 65th percentile
  57. 2026-08-05 19:15 UTCEPSS rescoreEPSS 1.2% · 65th percentile
  58. 2026-08-04 15:07 UTCEPSS rescoreEPSS 1.2% · 65th percentile
  59. 2026-08-04 10:35 UTCEPSS rescoreEPSS 1.2% · 65th percentile
  60. 2026-08-03 10:34 UTCEPSS rescoreEPSS 1.2% · 65th percentile
  61. 2026-08-02 08:45 UTCOSV refresh
  62. 2026-08-02 02:25 UTCEPSS rescoreEPSS 1.2% · 65th percentile
  63. 2026-08-01 04:13 UTCEPSS rescoreEPSS 1.2% · 65th percentile
  64. 2026-07-30 16:26 UTCEPSS rescoreEPSS 1.2% · 65th percentile
  65. 2026-07-30 01:28 UTCEPSS rescoreEPSS 1.2% · 65th percentile
  66. 2026-07-28 15:34 UTCEPSS rescoreEPSS 1.2% · 65th percentile
  67. 2026-07-27 14:10 UTCEPSS rescoreEPSS 1.2% · 65th percentile
  68. 2026-07-26 14:52 UTCEPSS rescoreEPSS 1.2% · 65th percentile
  69. 2026-07-25 14:16 UTCEPSS rescoreEPSS 1.2% · 65th percentile
  70. 2026-07-24 14:16 UTCEPSS rescoreEPSS 1.2% · 65th percentile
  71. 2026-07-23 14:16 UTCEPSS rescoreEPSS 1.2% · 65th percentile

Frequently asked(5)

What is CVE-2023-36459?
CVE-2023-36459 is a critical-severity vulnerability; its CVE record was published on July 6, 2023. Mastodon is a free, open-source social network server based on ActivityPub. Starting in version 1.3 and prior to versions 3.5.9, 4.0.5, and 4.1.3, an attacker using carefully crafted oEmbed data can bypass the HTML sanitization performed by Mastodon and include arbitrary HTML in oEmbed preview…
When was the CVE record for CVE-2023-36459 published?
The CVE record for CVE-2023-36459 was published on July 6, 2023. 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 November 21, 2024; the record at its source may have been updated since.
Is CVE-2023-36459 actively exploited?
CVE-2023-36459 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 1.2% probability of exploitation in the next 30 days (68th percentile of EPSS-scored CVEs).
What is the CVSS score of CVE-2023-36459?
CVE-2023-36459 has a CVSS v3 base score of 9.3 (NVD).
How do I remediate CVE-2023-36459?
A fix for CVE-2023-36459 is available: update to the fixed version the vendor names in its advisory.

Dependency Blast Radius

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